Unsure of dwell reading

[bytes311]

I just purchased a dwell meter and I'm trying to adjust my fuel mixture because it been tampered with in the past, however, I'm not exactly sure how to read it. I heard that it should fluctuate between ~30 and ~50 when the O2 sensor kicks in, but I just watched a YouTube video of someone adjusting their dwell with the same (or similar) meter, and his fluctuated around 20 and 30 on the bottom, 6 cyl scale. so now I'm not sure where mine is supposed to be.

Here is his video: https://youtu.be/MbE-2k4Cy4E

The first pic is where the needle sits before the O2 sensor kicks in. The second pic is what happens when I press on the full throttle switch.
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Edit: Here is my dwell reading: http://youtu.be/FTUJCUIWFhg

[Bitsyncmaster]

The book numbers use a 4 cylinder scale. So you read the 8 cylinder and double it with your meter. They used 4 cylinder to get more accuracy with the readout on meters that have selectable scales. They are really reading duty cycle but the dwell meter was a common mechanics tool that reads duty cycle on a different scale.

Duty cycle is a 0 to 100 % scale.

Dwell for 4 cylinder is 0 to 90 degrees.

[David T]

The book numbers use a 4 cylinder scale. So you read the 8 cylinder and double it with your meter. They used 4 cylinder to get more accuracy with the readout on meters that have selectable scales. They are really reading duty cycle but the dwell meter was a common mechanics tool that reads duty cycle on a different scale.

Duty cycle is a 0 to 100 % scale.

Dwell for 4 cylinder is 0 to 90 degrees.

Refer to D:04: 14-15. To verify you are getting correct readings set the WOT micro and you should read 50-60 steady (or 1/2 of that if you are reading on an 8 cylinder scale). That will tell you the Lambda ECU is at least getting power and you are able to get readings out of it. You may still have a contaminated O2 sensor. There are other checks to test the Lambda ECU without the O2 sensor. Adjusting the mixture is the LAST thing you do. You have to make sure everything else is perfect first. That includes spark plugs, ignition wires, vacuum leaks, valve adjustments, injectors, etc.

[Jonathan]

I just purchased a dwell meter and I'm trying to adjust my fuel mixture because it been tampered with in the past, however, I'm not exactly sure how to read it. I heard that it should fluctuate between ~30 and ~50 when the O2 sensor kicks in, but I just watched a YouTube video of someone adjusting their dwell with the same (or similar) meter, and his fluctuated around 20 and 30 on the bottom, 6 cyl scale. so now I'm not sure where mine is supposed to be.

Here is his video: https://youtu.be/MbE-2k4Cy4E

The first pic is where the needle sits before the O2 sensor kicks in. The second pic is what happens when I press on the full throttle switch.
34633

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Edit: Here is my dwell reading: http://youtu.be/FTUJCUIWFhg

How did this end up for you Daniel? What adjustments, if any, did you make? Mine is doing something similar to what you showed in your video.

[bytes311]

Hi Jonathan,

In my case, I installed new spark plugs and a new o2 sensor. I haven't had any issues with my dwell since.

[Ron]

Mine is doing something similar...If yours pulses, centered about the 20° mark, on the 8 cyl scale, it's good to go.

[Jonathan]

If yours pulses, centered about the 20° mark, on the 8 cyl scale, it's good to go.

At times it has, but not so much now. Let me summarize recent observations.

I have the Actron dwell meter. Also have a 3 mm t-handled hex wrench and my tamper proof cap was already removed when I got my car and the DMCH rubber plug has been in the hole ever since.

Most recently, including today, the car would idle immediately after starting from cold and the dwell would hold steady in that 50-60 range.

(The dwell numbers I am referencing are what is read off the 8 cyl scale and then multiplied by 2).

This would be the case for around one minute or two and then it would seem to hold steady at 44. It would keep holding steady at 44 for the majority of the time, even after I had warmed the car up enough idling to kick the cooling fans on and off.

At times, either by chance or the coincidence of revving the car up, it would pulsate instead of staying at that steady 44. The pulsation though is much higher than centering around 40 (what you meant by 20 deg, Ron) and it would be up to 75 and then down to 44 or so. It doesn't do this terribly consistently, as it seems to at times blip when going down to 44 and then want to pulsate around the 40 like I would want to see it do, but it will then either go back to the high and wide range pulsating or just hold steady at 44.

Early dwell measurements and other observations were pointing to my car being set rich, so I intended on leaning it out slightly. Upon removing the rubber plug, I could hear a distinct change in engine performance (affect from the vacuum leak?). I did make a small adjustment to the mixture screw, and would consider it "two hours" counterclockwise, in the sense that when I secured the 3 mm hex wrench, the handle was aimed at 10 pm and I went down to 8 pm (understandable?). I could put it back as it was easily if need be.

I did also notice that when you secure the wrench in the hole, you can push down the lever arm assembly that it is all connected to fairly easily and have the engine change pitch or sputter or whatever. I would assume that's to be expected after looking at the system diagram in the workshop manual and seeing what is going on under there.

The workshop manual diagnostic chart when seeing this steady at 40-50 mark, indicates the oxygen sensor is disconnected. I do not think mine is physically disconnected, not what is visible on the wire or connector anyway. I would think this is telling me the sensor is fouled or faulty one way or the other, yes?

I do have a replacement oxygen sensor I can put in but have not yet done so. I reread David saying everything else needs to be perfect, so assume a new and/or reliable oxygen sensor has to be in place before you can move on confidently to that final step of adjusting the CO mixture?

Consensus is to replace oxygen sensor as next step? yes/no?

[Chris 16409]

I was having similar issues and I replaced the Oxygen sensor, and it seems to have fixed the staying in open loop behavior. However, I also replaced one of the wires that bolts to the passenger side of the intake manifold that originates at one of the valley sensors. That could have been causing issues too.

[Ron]

At times it has, but not so much now. Let me summarize recent observations.

I have the Actron dwell meter. Also have a 3 mm t-handled hex wrench and my tamper proof cap was already removed when I got my car and the DMCH rubber plug has been in the hole ever since.

Most recently, including today, the car would idle immediately after starting from cold and the dwell would hold steady in that 50-60 range.

(The dwell numbers I am referencing are what is read off the 8 cyl scale and then multiplied by 2).

Same as mine. All Good here.


This would be the case for around one minute or two and then it would seem to hold steady at 44. It would keep holding steady at 44 for the majority of the time, even after I had warmed the car up enough idling to kick the cooling fans on and off.
I think it should have kicked in well before the fans kick in (59F according to the manual). I know I am too picky (Dave S tells me I worry about a lot of exact specks too much when I call and bug him sometimes, which I have found to be case), but I try to get them dead on anyway LOL...But I think this IS too far off. I'd confirm and suspect the temp sensor. But, that be the case, it is only late to switch and wouldn't change readings afterwards...


At times, either by chance or the coincidence of revving the car up, it would pulsate instead of staying at that steady 44. The pulsation though is much higher than centering around 40 (what you meant by 20 deg, Ron) and it would be up to 75 and then down to 44 or so. It doesn't do this terribly consistently, as it seems to at times blip when going down to 44 and then want to pulsate around the 40 like I would want to see it do, but it will then either go back to the high and wide range pulsating or just hold steady at 44.

Early dwell measurements and other observations were pointing to my car being set rich, so I intended on leaning it out slightly. Upon removing the rubber plug, I could hear a distinct change in engine performance (affect from the vacuum leak?).
I did make a small adjustment to the mixture screw, and would consider it "two hours" counterclockwise, in the sense that when I secured the 3 mm hex wrench, the handle was aimed at 10 pm and I went down to 8 pm (understandable?). I could put it back as it was easily if need be.
When I get one to where you describe above, it is usually a tad rich. "Two hours" is A LOT. Try moving it a little as possible CCW, in steps... It is touchy especially when you get it close. ...Drag it lean (say, swinging @ 35°) on purpose so you will know the range.
Note any time it is warm, idling, and it just sets there, you might have it so far off that it can't compensate.*
(I should mention I have see some I could not get to sit like this tho).

Yes, it's a vacuum leak. Always plug the hole with your finger, rev the engine once to clear it out and wait a bit for it to settle down, and then take a reading!


I did also notice that when you secure the wrench in the hole, you can push down the lever arm assembly that it is all connected to fairly easily and have the engine change pitch or sputter or whatever. I would assume that's to be expected after looking at the system diagram in the workshop manual and seeing what is going on under there.
Yep, normal.


The workshop manual diagnostic chart when seeing this steady at 40-50 mark, indicates the oxygen sensor is disconnected. I do not think mine is physically disconnected, not what is visible on the wire or connector anyway. I would think this is telling me the sensor is fouled or faulty one way or the other, yes?
Make sense. (As long as you don't have it WAY off as with * above).


I do have a replacement oxygen sensor I can put in but have not yet done so. I reread David saying everything else needs to be perfect, so assume a new and/or reliable oxygen sensor has to be in place before you can move on confidently to that final step of adjusting the CO mixture?
Absolutely.


Consensus is to replace oxygen sensor as next step? yes/no?Yes (If not as with * above.)

Did you do ALL of the tests in D:04:15?

[Bitsyncmaster]

I have seen a couple cars have dwell reading problems when the CAT is plugged. What I remember is you make the adjustment and it never seems to hold the dwell reading and swings way off again after it runs a little while.

[Jonathan]

Thank you for explaining all of that.

Ok, the adjustments are definitely not in terms of "hours." You're very right about that. I think my last adjustment put me back around 9:52 pm. Not that I can say it was that exact, but it was less than 10 pm, more than 9:30 pm and more than 9:45 pm too.

Here is what the dwell meter reading looked like before I shut the car off. I had returned the plug to the hole, and did not make any more adjustments after this reading was taken.


https://www.youtube.com/watch?v=HZuY7Fqc2Bo&feature=youtu.be

It isn't exactly in that 35-45 range with a centre point of 40, but it's close. I know what you mean about trying to get things exact and right to the specs, but my adjustments slightly more or less didn't improve it. It would either go to those larger swings higher or larger swings lower.

I have not test driven the car yet, but from what you see here, I could probably call it good enough and leave as is?

[Michael]

You should be seeing more action than that. In fact at watching it closely, the RPM increase at idle is the only thing causing any needle swing.

[Jonathan]

Ok. Here's what I know and some other things I need help in doing.

From that diagnostic chart, my "normal" operation seems to be the description of step "B" where you would see a steady 40-50 if the oxygen sensor was disconnected. Mine isn't disconnected to my knowledge, yet it stays in this steady reading of 44 and doesn't go into any kind of fluctuations on a regular basis. The video clip I shared earlier showed a reading I couldn't get it to do again, even after I felt it would have been plenty warmed up enough to start doing.

With that in mind, step "E" where you see a steady reading of 50-60 while cold, mine definitely does this. It goes to 51 right when you start the engine and stays for about 1 or 2 minutes. Pressing the flap on the full throttle enrichment microswitch will also make it go to this 51 reading and I confirmed that test just a few minutes ago. Releasing the flap has it go back to a steady 44.

A question for testing B, C, and D where you either disconnect the oxygen sensor, ground the connection directly or place a 1.5V battery between the connection and the ground, what is the best way to access it safely at home without a lift? I think at one point I found you could put the rear cradle on jack stands and then let the wheels hang free and you could reach over the wheel and under the wheel well and reach the connection on the oxygen sensor just as it butts up to the frame/grommet. Is this the best way or is there another better option?

[Bitsyncmaster]

So your getting the same reading during warm up as pressing the WOT switch? That makes me want to guess your lambda ECU is bad. Normally unless it very cold, your warm up dwell is less than WOT dwell. I also think your dwell readings are a little low which may just be your meter accuracy or the ECU.

You should try unplugging and plugging back in the lambda ECU connector. You may have a marginal connection. There are two or three grounds in that connector and the ECU is sensitive to having all them connected.

[Ron]

A question for testing B, C, and D where you either disconnect the oxygen sensor, ground the connection directly or place a 1.5V battery between the connection and the ground, what is the best way to access it safely at home without a lift?My wiring must be routed different than yours since I can get to it reaching over the passenger fender...
Anyway, don't worry about shielding, just use regular wire to make a temporary extension long enough to do it all under the hood.

[Ron]

+1 Michael
(... kind of like it kicks in and drops right out too. I have a guess....I'm going to go try to reproduce that first...)


So your getting the same reading during warm up as pressing the WOT switch? That makes me want to guess your lambda ECU is bad. Normally unless it very cold, your warm up dwell is less than WOT dwell. I'm thinking that is normal because the Full Throttle Enrichment Switch and the Thermal Switch (breaks ground @ 59F) are connected to pin 7 of the Lambda ECU. I.E. Same signal...

[Bitsyncmaster]

I'm thinking that is normal because the Full Throttle Enrichment Switch and the Thermal Switch (breaks ground @ 59F) are connected to pin 7 of the Lambda ECU.

Yes, I can't get over that summer has ended. Today was only 55 F.

[DMCMW Dave]

My wiring must be routed different than yours since I can get to it reaching over the passenger fender...
Anyway, don't worry about shielding, just use regular wire to make a temporary extension long enough to do it all under the hood.

Depends on how lowered your car is, how big your tires are, and how skinny your arms are.

[DMCMW Dave]

Yes, I can't get over that summer has ended. Today was only 55 F.

Remember he's in Canada. Probably already has a foot of snow on the ground. :wink:

[Horsebox]

I disconnected the stock lambda plug that terminated just before the drivers side bulkhead and rewired it so that you could disconnect the sensor easily from the engine bay. Had to get under the car to do this.

I've only just got the lambda system working on mine, it behaves differently to yours. The dwell sweeps back and front more like a windscreen wiper would. Yours looks very hesitant, like it's trying to go closed loop and then gives up for a bit, might be wrong tho!

They run like shit closed loop anyway. Set the mixture to 3% CO and it will be like a different car. :-)

[Jonathan]

Ok, smarta$$, so after I shovelled the snow out of my driveway.... nonsense!! lol

I got doing the diagnostic tests and here is what I found:

- was able to jumper the RPM relay socket yellow to brown and turn the system on without the key turned in the ignition. Frequency valve buzzing away... and loud considering nothing else in the engine was on and making noise.
- my oxygen sensor disconnected dwell reading was 51. My readings may indeed be a touch low as when I first got my Actron meter, the zero was not quite at zero, so I calibrated it down a touch.
- here's the goofy part... when connecting a wire to ground the connector to the frame or fender I get no change.

I went digging into the Lambda ECU area behind the driver's seat and inspected the connector bar on top of the ECU. This is the long, computer serial connector looking one (to avoid confusion). I can see where the bright blue wire coming in from the oxygen sensor combines along with another rubber sheathed one with it. Removing the outer plastic cover on that connector bar, I confirmed all the connections are good and also the bottom side where the female end of those tabs emerg. I was suspicious that one or more of the blue or shielded or other connection tabs had gotten spread apart a little too much and weren't grabbing well. Once you angle that bar into place, you can feel it tighten up, but you can't really see if one or more isn't connecting well within it.

I did this several times and still nothing on that oxygen sensor to ground connection test.

I didn't try the battery to ground connection test thinking it wouldn't matter if the circuit is open, but maybe that's not what that test is testing and could go back and try that one. Just say the word and I'll get it done.

What do you think? Is it that challenging to get that connector bar to firmly connect every wire or ground underneath and make things happy? Or is it simply that my Lambda ECU is toast? I see they have a silver and black one for sale on the DMCH webstore, they say interchangeable, so not sure what that's all about or why the price is slightly different?

[Ron]

Do the 1.5 v battery test...

[Jonathan]

Do the 1.5 v battery test...

Did the battery test.

Used a 1.5 V AAA battery out of a flashlight that was working before I removed the battery from it.

I hooked the battery up either with one end touching the connector end up under the wheel well and the opposite end connected to a piece of wire I then used to touch the fender or ground post at the rear fascia, or with the wire end touching the connector and the other end of the wire connected to the battery and touching the opposite end of the battery directly to the fender or ground post. Same result for all configurations (not sure if polarity is important in this test... is it?)... no change in dwell meter needle.

Dwell continued to read at 51, just like it would if the oxygen sensor was disconnected. Interesting enough, before I put things away, I reconnected the oxygen sensor with the RPM relay still jumpered and the dwell needle didn't change then either.

I did get a slight change in pitch to the buzzing of the frequency valve when I touched the battery to the connector and opposite end of the wire to the fender, but no change in dwell meter at all. Just that slight change in pitch (noise) to the frequency valve buzzing.

It's like the connector end for the oxygen sensor, doesn't actually come back through that blue wire and connect to anything. Not that any of these tests can show me anyway.

Ideas?

[Ron]

Sounds like the ECU is bad. But I would chase all of the wires going to it for continuity and that what is expected to be on them was there (12v, ground, etc.) especially the grounds before I purcha$ed one. Or, swap with a local owner for a test.

......you might try leaving the O2 sensor unplugged and do tests C & D right at the ECU (Pin 2, a blue wire). The positive (+) end of the 1.5 V battery goes to the harness and the base to ground. (Try to ground it on the right hand air horn where the harness ground wire mounts, fwiw).
...maybe a bigger battery...not sure but I always used a D.

EDIT: If the O2 sensor is not HOT it will not output voltage or cause a change when you hook it up (why engine should be running and fans kicked in once for test(s)).

[Bitsyncmaster]

Shielded wire protects the inner wire from picking up noise from other wires running close to it. Normally only one end of the shield is connected to ground. The shield should not be conducting any current to work correctly and that is why only one end should be connected. I have not verified our stock wiring did followed this rule.

Also you may not have a fender grounded if your missing one of the fender ground wires. It's best to get a long wire for your testing that grounds your meter to the engine block or battery negative post. I carry a 20 foot wire with alligator clips on each end for testing circuit problems. That way I can always use the battery ground as my reference.

[Jonathan]

Good morning! :)

Some more things I can test to try and figure it out. I'll repeat the battery to ground test using the polarity you mentioned as well as a bigger battery (I have a C battery handy but no D at the moment).

I was looking at the wiring diagrams trying to see what bulkhead connections I should look closer at and saw something worth clearing up from the main wiring diagram and the separate Lambda circuit diagram.

Here are both:

3710537106

I was scanning these looking for where the grounds were on that bar connector for the ECU and noticed they are not consistent with which location has the blue wire from the sensor and which location has the black shielded one. They are using locations 2 and 4, but have them reversed when you compare diagrams. Can someone confirm where the blue wire goes, spot 2 or spot 4?

I see the grounds are identified as being on spots 5 and 16 so I'll confirm those are in place too.

When I was doing the ground test yesterday, while I agree with you that my fenders may not have all their ground wires correctly in place, I did use a long enough wire to bring it all the way up to make contact right at the top of the engine block, on the same post that my dwell meter is grounded to. I can just as easily string it over to the negative ground on the battery itself though too.

[Jonathan]

My blue sensor wire is on pin 2. That, the grounds on the connector and the other wires all look fine. I don't feel at this time it is the connector itself that is the problem.

I also redid the ground that connects to the silver Lambda ECU bracket/box itself just to ensure there wasn't any corrosion under there messing things up.

I repeated the sensor ground test as well as the one with the battery (type C this time). No change in any way to the dwell meter needle while doing these tests, ground, battery, disconnected, none of them affected it.

I am leaning towards a replacement silver lambda ECU at this point, or at the very least, to swap in a known good one to test my car to ensure the one that's in there is faulty.

[Ron]

Dang it Jonathan!...now you have me worried ;-)

As posted a while back, mine fails the ground test (goes slowly to 77° then settles on 44°) BUT no problems...
Comparing schematics, I found this in the Workshop Manual D:04:12
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Good eye, J! ...off to the shop to take a look, arggggg....

[Ron]

Mine is not like D:04:12 -- It is like this:

37110

I'd try another unit.

[Jonathan]

I'd try another unit.

Like "try another unit" for testing?

Yea, agreed. Gotta get my hands on one first though. Current exchange rates and costs and shipping and whatnot makes everything online x2 to get it to me in Canadian funds. So a new, silver Lambda ECU at $156 USD will be well over $300 CAD once all is said and done.

On the subject of that blue wire showing up on some diagrams in the #4 spot as opposed to the #2 spot, do we know of anyone that actually has their connector wired so that it is in the #4 spot? Sounds like yours is in the #2 spot and so is mine. Is this anything to do with what the difference between the "black" Lambda ECU is suitable for and what the "silver" one is for? It says they are interchangeable, so if that is the case, I don't know why someone would buy the more expensive one? $125 for the black gets it home to me for closer to $250 CAD.

[Ron]

Yep, for a te$t!

Yes, I bet they all are all like ours...just an error on the one schematic in the workshop manual (and on a lot of 3rd party interpretations. One of the popular color ones has 2 & 4 tied together, NFW!).

RE silver/black/interchangeability- I think #4 is a ground for the shield (and its only connection, as Dave mentioned) for either black or silver. Mine is untouched and that way. ...can't swap input and ground on interchangeable units.
I am going to test the two sometime during the middle of next week and will post results (assuming I get rid of the ground test error fairly soon after it arrives).
(I'm sure there are some who would buy the more expensive one for originality. Not me tho ;-)

[Jonathan]

Let me know how it goes. I don't need to buy the more expensive one for originality if they indeed work the same. Although I don't want to spend that sort of cash on something that isn't quite right if we don't know for certain what the differences are.

In the meantime, while I don't have a spare handy, is there anything else you can think of for me to test with my current unit, in or out of the car, or with the wiring in the car? I could test those things you mentioned briefly about the ground being grounded or the 12 V having 12 V but I wasn't sure how I might go about doing that. If I pop the connector off to access the underside of the connector, could I test the wiring side from there? I was thinking I could do continuity from the connector to the end of the oxygen sensor connector, but that's not all that helpful I'd assume 'cause it's only about 2 feet away and I can visually see about the entire length of the wire. The other wires disappear into the harness jumble and go somewhere else. The bulkhead connections diagram wasn't too specific on which ones I would confirm are ok. Any ideas?

[Bitsyncmaster]

Probably good to do a continuity test on the ground pins. You never know if any cars left the factory with all the pins connected because the engine would probably work with one missing.

I installed a hot start relay in another owners car last month and his hot start relay socket had one pin stuck in the wrong socket pin. It probably was done that way at the factory and never caused any problem because the hot start relay was not used.

[Bitsyncmaster]

With both of you showing the same problem, I would not think the ECUs would just happen to fail the same way. So if Ron finds the replacement ECUs do the same thing, I suggest you try to open the light/green wire going to pin 7 of the ECU and see if that fixes the problem. Of course you won't get the WOT rich adjustment but it would point you to something in the Thermal Throttle sensor.

I suggest this because I remember seeing some funny results with the lambda ECU if that WOT line was on when the lambda was powered up. I cut that wire on my car because I use a wideband and switch to a richer mixture myself rather than only have the WOT do it.

[Michael]

Dave once told me the way to test a ECU was to replace it with a known good one. I found out that sometimes if you are lucky you can take one look at the board and tell it's bad. Not sure how "lucky" that is that I needed a new ECU, but I did diagnose my problem quite easily.

[Bitsyncmaster]

Dave once told me the way to test a ECU was to replace it with a known good one. I found out that sometimes if you are lucky you can take one look at the board and tell it's bad. Not sure how "lucky" that is that I needed a new ECU, but I did diagnose my problem quite easily.

You can open the lambda ECU quite easily. Just two screws on the bottom hold the board in. The unit has a custom board mounted to the main board to input the O2 signal. That section would be a nightmare to fix. The unit seems built pretty good but I did replace the transistor driver for the FV output to a MOSFET a long time ago to reduce the power.

[Jonathan]

This is where some of the mixing of names for the same parts gets me confused.

Ok, so, LIGHT GREEN wire at pin 7 of the Lambda ECU goes to the full throttle enrichment switch and the thermal switch. For sake of clarity, the full throttle enrichment switch is the "microswitch with flap (p/n 102784). The thermal switch is p/n 102478 on that same diagram (2-3-0) but is referred to as the "switch, lambda sensor" in the parts list. Is that correct?

The lambda probe/oxygen sensor is p/n 101069 also on page 2-3-0.

The thing is though, and I hadn't thought they were directly related, and may still not be, but I have had the "idle speed regulator switch (thermistor)" p/n 102480 jumpered since late last season. I did this as I suspected it got unplugged under the valley and was causing a high idle condition where it got stuck at 2,000 RPM. Not needing to go into the valley right that minute, the solution was to jumper those two connections (black/yellow to black/slate) right at the connector on the idle speed ECU to trick it into thinking it was there. I understood this was going to be fine unless ambient temperatures were cold and then maybe that's why I'm where I am?

That LIGHT GREEN you're talking about Dave is separate though, isn't it? I hate having a bandaid in place while trying to sort something else out, but left it as is for not wanting to go into the valley until I absolutely had to. I think this second light green sensor is just on the side of the engine opposite the throttle spool, right? I could disconnect that pretty easily too if it would help testing.

[DMCMW Dave]

One thing I don't think I see mentioned. There is a ground wire on the forward (back of the engine) end of the intake runner on the passenger side. If unmodified, it has a red tag on it, and the wire is only about 3 inches long before it hits another connector. THIS WIRE is the ground reference for the O2 sensor. If disconnected, the ECU goes kind of nuts. Check continuity from that attachment point all the way to the ECU, and check for bad connections at the bulkhead connection and at the connection close to the intake runner.

[Ron]

For sake of clarity, the full throttle enrichment switch is the "microswitch with flap (p/n 102784).
The thermal switch is p/n 102478 on that same diagram (2-3-0) but is referred to as the "switch, lambda sensor" in the parts list.
The lambda probe/oxygen sensor is p/n 101069 also on page 2-3-0.
Yes.


The thing is though, and I hadn't thought they were directly related, and may still not be, but I have had the "idle speed regulator switch (thermistor)" p/n 102480 jumpered since late last season. I did this as I suspected it got unplugged under the valley and was causing a high idle condition where it got stuck at 2,000 RPM. Not needing to go into the valley right that minute, the solution was to jumper those two connections (black/yellow to black/slate) right at the connector on the idle speed ECU to trick it into thinking it was there. I understood this was going to be fine unless ambient temperatures were cold and then maybe that's why I'm where I am?"Cold" can be misleading...I'm not sure if it makes or breaks ground (makes iirc), but it is at 59F. ...I don't see it as a problem WRT dwell readings. (But then there are always those "undocumented features" ;-)
Note another error in the manual, they call it "152 ...micro switch".


That LIGHT GREEN you're talking about Dave is separate though, isn't it? I hate having a bandaid in place while trying to sort something else out, but left it as is for not wanting to go into the valley until I absolutely had to. I think this second light green sensor is just on the side of the engine opposite the throttle spool, right? I could disconnect that pretty easily too if it would help testing.
Light Green goes from the Full Throttle Switch (AKA "WOT Switch", "Throttle Enrichment Micro Switch", 150) to the Thermal Throttle Enrichment (AKA "Thermal switch", "switch, lambda sensor", 149 ) then to the Lambda Electronic Control Unit (ECU), as mentioned in post 17.

==========

+1 Dave S! (and why I suggested using the ground on the right air horn...)

I'm not going to say it is always the grounds somehow.

[Bitsyncmaster]

The idle speed thermistor you jumpered on the idle ECU has nothing to do with the lambda ECU. So no, your jumper is not causing your lambda problem.

[Jonathan]

One thing I don't think I see mentioned. There is a ground wire on the forward (back of the engine) end of the intake runner on the passenger side. If unmodified, it has a red tag on it, and the wire is only about 3 inches long before it hits another connector. THIS WIRE is the ground reference for the O2 sensor. If disconnected, the ECU goes kind of nuts. Check continuity from that attachment point all the way to the ECU, and check for bad connections at the bulkhead connection and at the connection close to the intake runner.

Ok, still a work in progress as I have to run out for a while today, but this is at least part of my problem (or all of it).

Good description on that red tag, short wire and connector as mine was exactly as you mentioned it. I disconnected the connector and checked for continuity with my multimeter from the engine block side of the connector to another ground on the engine block and got nothing.

It may have just been the male end of that connector being corroded, but while extracting it, I snapped off the bolt. Oh well, that's another on the list as I have one right above it for the air filter housing that's the same story.

I won't mess with extracting it right now, but will figure out where else to attach that ground instead. I was rigging up some test wires just to confirm and realize how valuable alligator clips would be.

Like I said, I'm heading out, so will do this properly when I return, but just wanted to mention what I found when testing this ground initially.

[Jonathan]

Almost there!!

I redid the ground for the O2 sensor at the engine block location Dave mentioned. Rear of engine, passenger side, at the end of the intake near the top but on the side somewhat. Mine had the red tag as mentioned and I found there was a problem through the connector. While getting the grounding bolt out of the block, it snapped off. I put the replacement ground right near it, in the bolt hole for the air filter housing at about 12 o'clock. That ground tested ok for continuity.

I went back and tested the O2 sensor wire to ground and the needle went up like described in the workshop manual. Also got the battery test to work where the needle goes way down. I reconnected the O2 sensor (existing one) and put everything back together.

Testing the dwell with the car running gives me the same "lazy" O2 sensor as I had before. I can get it to "wake up" by revving he engine, but then it tends to fall back out and I get the steady dwell reading at around 44 until racing the engine again. My next step is to replace the O2 sensor as I believe fixing that ground helped me rule out a bad lambda ECU.

[Ron]

Jonathan,
I played with the CO and found I can reproduce your symptoms exactly by turning the adjustment screw to an extreme. If the new O2 sensor doesn't resolve things, I would suggest you purposely set the dwell to ~20° and turn it as little as you can in steps until you walk it up to 40°, as previously mentioned.
fwiw, I can make mine do this every time.

===============

As promised, here are the results when using a Silver v/s Black Lambda ECU:
I found no significant difference but note I can not trust this 100% because with ALL units I got a rise to 77° followed by a fall to 44° (steady) dwell reading when grounding the O2 sensor harness wire(disconnected) v/s 87° minimum (steady) called out in the manual. (See * below)

I swapped (a different) Black and Silver unit out three times in a row and performing all of the tests in the manual. Results were consistent.
The Silver read 3° dwell lower than the Black when disconnecting the O2 Sensor (41° v/s 44°, both within specs).
The Silver was ~1/2 second slower to respond when grounding the O2 Sensor harness wire.

===============

* The following may be helpful to someone suspecting the Lambda ECU or its wiring.
ANY comments, especially suggestions to make it exhaustive (?I think it is?), would be appreciated!

I chased all wires going to the unit and tested them with an ohm meter for continuity.
After finding no problems, I used an ice pick probe to improve the tests (Adds a load...):

Lambda ECU Harness Plug Disconnected -- ALL tests!
Key in RUN position.
With Ice Pick Light connected to Battery Positive(+), the following should make the light burn BRIGHT:
02 When jumping harness side of O2 Sensor Plug to Ground. (Disconnected)
05
07 COLD (<59°F) (See ** below) (Note: This, with following test, checks the Thermal Throttle Enrichment Switch operation also.)
07 WARM (>58°F) NO LIGHT; Lights when pressing Full Throttle Micro Switch.
16
XX Black Ground Wire under Phillips Screw (Disconnected).

With Ice Pick Light connected to Battery Negitive(-), the following should make the light burn BRIGHT:
08 When jumping pin 30 to 86 (Brown to Yellow/Red) on #106 Main Fuel/Lambda Relay (Installed). (Note: Tests Lambda Relay also)
15 When jumping Battery(+) to the Red/Brown wire in the Frequency Valve Plug (Disconnected).
17 When jumping Battery(+) to the Orange Diagnostic Plug Wire.
All other pins are unused.


** I used an appropriate "freon" with a hose directed toward the thermal switch area in the VOD to bring the temp down, followed with compressed air to clear area out after testing.

===============

Being at a lost WRT it failing the test, grounding the O2 harness wire, I took a heavy gauge copper wire and connected it to Battery(-), right air horn screw for the reference ground wire, and the Phillips screw for the ground wire on the ECU case.
No change...:headscratch:

EDIT: I forgot to mention I found a crack in the nipple I used to seal the Oil Filler Cap when the Breather is off, and EVERYTHING, but the one test, is fine now.
Cue Dave telling my picky arse to find something else to worry about...???

[Jonathan]

Interesting way you described the initial disconnected wire test, Ron, because I would describe what mine does in exactly the same way. Mine doesn't go all the way up to 87 and hold steady either but instead comes close but then falls back down. Hmmm...

So I'm a little gun shy on replacing my oxygen sensor. Not because I don't think it could stand to be replaced from likely being wonky, but because of the fear of snapping it off in the exhaust pipe and dealing with that nonsense. So, while I got a proper oxygen sensor socket and had everything pretty much ready to go, I chickened out (McFly).

Before I put the rear wheel back on and still had good access to the connector, I ensured the sensor wire was all the way into the opposite end and it felt like it was snug, maybe more than it had been before. The grommet/boot thing kind of makes it hard to know for sure it went in properly and made a good connection.

I lowered the car and fired it up and it idled ok. After it got warm/hot, my oxygen sensor would wake up but I admit, mostly only after racing the engine some. It stayed going for a while and then after an adjustment or two to the mixture, would fall asleep again. Rev the engine some more and it wakes up but then falls off again.

So, with that lower the reading to 20 extreme and then dial slowly back up to 40, just to confirm, to get the numbers to lower means you adjust the mixture richer, and then to get the numbers to go up you adjust the mixture leaner? Is that correct? It doesn't seem intuitive, like it feels like it should be the other way, but I understand that to make the numbers go down, you adjust richer (i.e. clockwise)?

I saw the reading go pretty low, but it wasn't steady at 20, instead it was fluctuating from as low as 10 (5 on that 8 cyl scale) and up to 30 or more, but not much more, maybe 35. I'd say it was centred around 20 if that's what you meant.

I did dial it back leaner some more, maybe close to 9:30 pm using my old reference by the time I stopped. It just seemed to fluctuate well for a little bit but then fall asleep again. The car's cooling fans had come on by the end of my testing, so the engine was not cold by any means. I did see the last couple ranges be pretty close to the ideal 35-45 and a fairly tight swing, not wild like before.

That's where I said good enough for the time being. No need to dwell on it any more. Not until I either take it to a shop with a torch to do the sensor for me or perhaps grow a set myself and then have at it a little more fearlessly. It's also October and the car can just sit there until the Spring if need be. I'm a little tapped out on the DeLorean experience for the moment.

[Ron]

Short and sweet - We are on the same page/understanding WRT everything you said.
Only comment is I don't see the O2 sensor solving the ground test issue since it is unplugged during the test.

:banghead:

[Jonathan]

Ok, this helps. I hadn't realized our cars were doing such similar things. When you mentioned the ground test results, I thought it was a case of the description in the manual being a misprint and what we both got being ok. I guess not.

So agreed that's a good place to focus on figuring out what is going on. More so than a new oxygen sensor is for certain.

Is there any other cars that have the same "blue on two" wiring connection as opposed to the way some of those other schematics show it? Or did we already determine our wiring is fine, and just like every other car, and it is just some of the documentation that isn't right?

This electrical business isn't how I'm programmed to think, lol. I'm more pumps and piping. If a signal like we're supposed to see isn't staying at 87 when grounded, it seems like the ground slowly dissipates. If we don't physically move the wire off the ground, what could cause that to weaken? Or better yet, what circuit would "take over" in a path of least resistance kind of way that shows us the grounded almost 87, but then before we quite get there, it switches back over to the stuck on 44 reading? I am pulling guesses out of thin air, so bare with me, but is there some mode or relay that latches and is supposed to stay where it is, but ours isn't and thus defaulting back over to this other rest position. I really don't know how the inside of that box works, so not sure what could have gone wrong.

If it isn't the box though, as you say both of yours do the same, what else is in the circuit elsewhere in the car that could be doing this? Like something else that thinks it defaulted back over to the sensor being disconnected mode.

I'll try to look at it closer tomorrow with the drawings in front of me. I got baseball playoffs on in front of me at the moment!

[Ron]

I think the wires are right. "Blue on two" doesn't make sense and with the manual contradicting itself, I'd blame the different versions on a (the) misprint. But who knows, I'm baffled.

[Jonathan]

Baffled... si, senor! :)

I assume others (Dave for example), can get a normal car to do that grounded test and see their dwell reading go up to 87 and stay there?

Time to play "one of these things not like the other?"

[Bitsyncmaster]

Here is a photo of a spare lambda cable I have.

I would not worry much about the book test to short and use a battery to read specific values of dwell. It's not a real world operation. The O2 sensor is an open circuit when cold and provides a 0.50 volt value at lambda 1.0.

So if you want to test your ECU, just adjust the mixture lean and rich to read the minimum and maximum dwell values.

I have never done the short and battery test on the O2 signal. So maybe mine does the same as your seeing.

[Ron]

I assume others (Dave for example), can get a normal car to do that grounded test and see their dwell reading go up to 87 and stay there?Several people (everyone I asked) say it stays at 87° as long as it is grounded (one 2 minutes and he quit).

[FABombjoy]

You can also ground terminal 11 on the k-jet box and send the duty cycle to 90+%.
WOT switch sets it to ~60%

I'm not sure how those translate to degrees when using a dwell meter.

I once tried to measure duty cycle (using an Innovate data logger) using the valve outputs and not the test wire / connector. The readings were about 50% all the time. Once I switched to the proper test connector they started to make more sense.

[Jonathan]

Here is a photo of a spare lambda cable I have.

I would not worry much about the book test to short and use a battery to read specific values of dwell. It's not a real world operation. The O2 sensor is an open circuit when cold and provides a 0.50 volt value at lambda 1.0.

So if you want to test your ECU, just adjust the mixture lean and rich to read the minimum and maximum dwell values.

I have never done the short and battery test on the O2 signal. So maybe mine does the same as your seeing.

I got around to taking some pictures today.

My wiring on the lambda connector looks about the same as yours does Dave.

3725037251

[Jonathan]

Just a little update on my own car for this thread.

You can put me in the "a new O2 sensor made a world of difference" group. I took the car down to the mechanic I used a lot in the first couple years of ownership. Yea, that was on Wednesday, October 21st, 2015 and I thought, what the heck, looks like a good day to get it done.

He swapped out the sensor without any trouble of snapped threads or seized exhaust fittings and then he also helped me get the mixture adjustment right. He has a lot of experience with K-Jet and Bosch systems and that was a big reason I went to him originally. He showed me the range from stall to stall for the adjustment and it was no more than 12 to 6 o'clock, if we use the hands on the clock analogy again.

A bit of rain dampered the day on Wednesday, but it was beautiful on the Friday. I got a couple 100 km on the car that day and it drove great. That mechanic said something similar after he took it for a short test drive too. He mentioned how quiet and solid it felt now compared to back in 2007. I've done rear axles and other suspension work since then, but he meant also the interior and that everything just seemed tighter. That was nice to hear as well and a compliment on a lot of other work I've done trying to get that car right.

Anywho, it was a good day for me and a good day for the car. Cheerio!

[David T]

Sounds like he adjusted the mixture by ear. It is too sensitive to do it that way. The better way is to hook up a dwell meter and use the procedure. 1/16 of a turn can make a big difference, 1/2 turn is a LOT! It will have a large effect on your gas mileage, tuning by ear usually results in a richer mixture than necessary.

[lazabby]

I'm trying to tune my car using a dwell meter but it either doesn't work or the diagnostic plug is not working. I'm reading about 8 volts in the plug but when I switch to the dwell setting nothing happens. I vaguely remember someone mentioning there is a place in the bulkhead where the dwell meter can be connected to check things. Does anyone remember where that is? Otherwise I may try connecting directly to the CO2 sensor. If that doesn't work then I may need to try a different dwell meter.

[Bitsyncmaster]

I'm trying to tune my car using a dwell meter but it either doesn't work or the diagnostic plug is not working. I'm reading about 8 volts in the plug but when I switch to the dwell setting nothing happens. I vaguely remember someone mentioning there is a place in the bulkhead where the dwell meter can be connected to check things. Does anyone remember where that is? Otherwise I may try connecting directly to the CO2 sensor. If that doesn't work then I may need to try a different dwell meter.

One lead of the dwell meter goes to ground (engine block is fine) and the other lead can connect right on the frequency valve wire red/brown. The FV has a two pin connector (it may be three pin but only two wires) on the bulkhead. You test your reading by pressing the wide open throttle switch and the meter should read 54 degrees.