Dwell at 60 all the time

[CFI]

Trying to chase down the cause of my poor gas mileage (currently 16mpg). Finally purchased a dwell meter and tested my engine. Dwell is approx 60 when started (cold engine, 80*f outside temp). It varied a little bit for the next ten minutes but not much. It pretty much stayed around 60. I’m guessing the O2 sensor is not operating.

Stage II engine, automatic trans, WOT switch disconnected (it was stuck on causing a high idle condition). Idle is right around 800 and steady once a little warmed up.

I’m going to test the O2 sensor next. Does .5 volts seem right for a warm engine with a correctly operating O2 sensor?

[Bitsyncmaster]

Yes 0.5 volts is about what you get on the narrow band O2 sensor. Since you said your not changing much from 60 deg. I also would suspect the O2 sensor is bad.

[CFI]

Yes 0.5 volts is about what you get on the narrow band O2 sensor. Since you said your not changing much from 60 deg. I also would suspect the O2 sensor is bad.

Thanks. For the life of me I can not find the O2 sensor connector. I see the wire, but can not follow it. There just isn’t enough room. Can I cut the wire and splice in a new sensor?

[dmcnc]

You should be able to pull on it until it comes out the rear frame crossmember. Otherwise you could splice the new sensor as well.


Thanks. For the life of me I can not find the O2 sensor connector. I see the wire, but can not follow it. There just isn’t enough room. Can I cut the wire and splice in a new sensor?

[Chris 16409]

Do you have the rear left wheel removed? You should see the plug socket coming out of the fiberglass tub.

[Bitsyncmaster]

Yes there should be a connector on the drivers side wheel well. If not a PO may have pushed it through into the ECU compartment behind the drivers seat.

[FABombjoy]

I would make a quick check at the WOT switch harness and ensure light green wire isn't grounded. 60 would be the magic number for the lambda enrichment mode. You might have a pinched wire or shorted thermal enrichment switch.

[CFI]

Yes there should be a connector on the drivers side wheel well. If not a PO may have pushed it through into the ECU compartment behind the drivers seat.

I found it. Someone zipped tied the O2 sensor wire to the left rear spring. I cut the tie, pulled on the wire, and found the connector.

[CFI]

I would make a quick check at the WOT switch harness and ensure light green wire isn't grounded. 60 would be the magic number for the lambda enrichment mode. You might have a pinched wire or shorted thermal enrichment switch.

Good idea. I’ll double check.

[Bitsyncmaster]

60 % duty cycle is what it would be if the WOT is on. It would not vary at all. Dwell would be at about 54 deg also not varying at all.

[FABombjoy]

It would not vary at all
You may see some variance on a digital meter. Here's an old data capture of my car in warm-up mode.
59870

[CFI]

Here the results of this mornings test.

OAT is 70F

Cold engine, just after starting 1.02 - 1.04 volts at O2 sensor
After 1 minute, .98 volts.
After 3 minutes, .97 volts

Then, at 4 minutes the engine idle started hunting, a little at first, then from 800- 1,500 rpms over and over again.
At this point the volts steadily climbed up to 1.4 where it stayed until I turned the car off. Exhaust smells obnoxiously rich through the whole test.

I don’t know if it means anything but the volts didn’t drop immediately after turning off the engine. It just slowly worked it’s way down to zero.

[CFI]

I just thought of something. Whenever I start my car I always turn on the electricity and let the fuel pump finish priming before I start the engine (Dave's RPM relay). Doing this, I always hear a humming sound from the engine and I didn't think anything of it. Today I turned on the electricity, the pump primed, and I opened the engine covers to see what was making that noise. It was the cold start valve. I thought it was only supposed to run during cranking? Perhaps the cold start valve is running all the time?

[Bitsyncmaster]

Here the results of this mornings test.

OAT is 70F

Cold engine, just after starting 1.02 - 1.04 volts at O2 sensor
After 1 minute, .98 volts.
After 3 minutes, .97 volts

Then, at 4 minutes the engine idle started hunting, a little at first, then from 800- 1,500 rpms over and over again.
At this point the volts steadily climbed up to 1.4 where it stayed until I turned the car off. Exhaust smells obnoxiously rich through the whole test.

I don’t know if it means anything but the volts didn’t drop immediately after turning off the engine. It just slowly worked it’s way down to zero.

The sensor should have no voltage until it warms up. This is sounding like your lambda ECU is bad. When I program my wide band I set the wideband output to 0.5 volts and to swing fast higher or lower if the AFR is not what I want. The wideband feeds the OEM lambda ECU directly into the O2 input circuit.

[dmcnc]

Cold start relay or cold start valve? I know the Idle motor buzzes when the key is on run. It's also right next to the cold start valve. Sure it's not that? The CSV is easy to test of course.

[Bitsyncmaster]

Cold start relay or cold start valve? I know the Idle motor buzzes when the key is on run. It's also right next to the cold start valve. Sure it's not that? The CSV is easy to test of course.

+1
Unless you have my idle ECU the idle motor will run (buzz) when ever the key is on.

[CFI]

Cold start relay or cold start valve? I know the Idle motor buzzes when the key is on run. It's also right next to the cold start valve. Sure it's not that? The CSV is easy to test of course.

Cold start valve. I touched it and felt it vibrating. I'll unplug it and see what happens.

[Bitsyncmaster]

Cold start valve. I touched it and felt it vibrating. I'll unplug it and see what happens.

The CSV should only get power when the starter is cranking the engine. Make sure your bulkhead connectors are plugged into the correct mating connector.

[CFI]

I unplugged the cold start valve and the noise is not coming from that, it's coming from the idle motor. Running without the cold start valve made no difference.

[CFI]

The CSV should only get power when the starter is cranking the engine. Make sure your bulkhead connectors are plugged into the correct mating connector.

Connectors look good but the blue one has a wire that was cut out.59873

[Jonathan]

More info on those WOT (wide open throttle, or full throttle) microswitches here: http://dmctalk.org/showthread.php?13623-Quick-question-what-s-this-switch

You mentioned having an automatic. You will have two of those WOT microswitches. One is for fuel enrichment and the other is for kicking down the auto trans into passing gear when you hammer the gas. Both of those switches plug into a Tetris puzzle looking connector and both can be plugged into either switch. While the switch itself doesn't matter (flap or no flap, they both activate at the same time), the pair of wires on the car side coming from those connectors does matter. Confirm both pairs are fine and not shorted or mixed up. The wire pairs look very similar, especially 38 years later with a lot of fading and engine filth, but one of them is 'light' green and the other is just green.

[CFI]

More info on those WOT (wide open throttle, or full throttle) microswitches here: http://dmctalk.org/showthread.php?13623-Quick-question-what-s-this-switch

You mentioned having an automatic. You will have two of those WOT microswitches. One is for fuel enrichment and the other is for kicking down the auto trans into passing gear when you hammer the gas. Both of those switches plug into a Tetris puzzle looking connector and both can be plugged into either switch. While the switch itself doesn't matter (flap or no flap, they both activate at the same time), the pair of wires on the car side coming from those connectors does matter. Confirm both pairs are fine and not shorted or mixed up. The wire pairs look very similar, especially 38 years later with a lot of fading and engine filth, but one of them is 'light' green and the other is just green.

The WOT connector was disconnected several weeks ago but I’ll double check the wiring.

[Ron]

+1 Luke

=====

$.02

For the early harness (and others iirc):
The Throttle Enrichment Switch has a Light Green wire (LG).
The Full Throttle Switch (WOT) has a Light Green with a Green Stripe wire (LGG).
Both have a Black wire. If they are correct the others don't really matter (the switches make/break ground together).

Disconnect the LG wire at Pin #7 of Lambda Control Unit to eliminate the 2 micro switches, the Thermal Throttle Enrichment Switch (in the VOD, Y-Pipe), and their wiring as being the cause of over enrichment.

[CFI]

+1 Luke

=====

$.02

For the early harness (and others iirc):
The Throttle Enrichment Switch has a Light Green wire (LG).
The Full Throttle Switch (WOT) has a Light Green with a Green Stripe wire (LGG).
Both have a Black wire. If they are correct the others don't really matter (the switches make/break ground together).

Disconnect the LG wire at Pin #7 of Lambda Control Unit to eliminate the 2 micro switches, the Thermal Throttle Enrichment Switch (in the VOD, Y-Pipe), and their wiring as being the cause of over enrichment.

I will try that tomorrow, thank you

[Lukas]

+1 Luke

=====

$.02

For the early harness (and others iirc):
The Throttle Enrichment Switch has a Light Green wire (LG).
The Full Throttle Switch (WOT) has a Light Green with a Green Stripe wire (LGG).
Both have a Black wire. If they are correct the others don't really matter (the switches make/break ground together).

Disconnect the LG wire at Pin #7 of Lambda Control Unit to eliminate the 2 micro switches, the Thermal Throttle Enrichment Switch (in the VOD, Y-Pipe), and their wiring as being the cause of over enrichment.

Wow that's great info...I have the two plugs, but only one used (in a manual car). I'll have a closer look as I never noticed the different colors.

At least in a manual car, the correct plugs seem to matter. I have done some continuity testing, and found that the throttle enrichment switch plug is normally open, and grounded when the microswitch closes. However, my unused kickdown switch has continuity, even though it's left dangling in the engine bay?!

[CFI]

Is this my diagnostic plug? If so, what’s the purpose of the jumper wire?59874

[CFI]

Disconnected light green wire from Lambda ECU. Disconnected O2 sensor per Lambda System Operation Check guide.

Cold engine, OAT 75F

Frequency valve dwell (4cyl scale) on startup: 45.5 and pretty steady

Grounded O2 sensor wire to ECU: dwell steady at 85 (should be 87 per manual)

Applied 1.5 volts to O2 wire to ECU: dwell jumps to 85 (should be maximum of 20 per manual)

Disconnect 1.5 volts: dwell returns to 45 and steady

Thoughts?

[CFI]

I should clarify that the dwell I was testing at the beginning of this thread was distributor dwell. That holds steady at 60. This recent test is frequency valve dwell.

[Bitsyncmaster]

Disconnected light green wire from Lambda ECU. Disconnected O2 sensor per Lambda System Operation Check guide.

Cold engine, OAT 75F

Frequency valve dwell (4cyl scale) on startup: 45.5 and pretty steady

Grounded O2 sensor wire to ECU: dwell steady at 85 (should be 87 per manual)

Applied 1.5 volts to O2 wire to ECU: dwell jumps to 85 (should be maximum of 20 per manual)

Disconnect 1.5 volts: dwell returns to 45 and steady

Thoughts?

I think your lambda ECU is bad. From you past posts, it seems like something is pulling up the O2 input to the lambda. I have some extra lambda ECUs but it takes a medium flat rate box to ship it.

[FABombjoy]

he dwell I was testing at the beginning of this thread was distributor dwell.

https://www.youtube.com/watch?v=2sF4MU1txTY

You were measuring distributor dwell but talking about the O2 sensor & Lambda system? Those are completely disparate systems. :D

[CFI]

https://www.youtube.com/watch?v=2sF4MU1txTY

You were measuring distributor dwell but talking about the O2 sensor & Lambda system? Those are completely disparate systems. :D

I know. I’m running several tests for different reasons. Sorry for the confusion

[CFI]

I think your lambda ECU is bad. From you past posts, it seems like something is pulling up the O2 input to the lambda. I have some extra lambda ECUs but it takes a medium flat rate box to ship it.

Thanks Dave. I’ll send a PM later today.

[Ron]

Is this my diagnostic plug? If so, what’s the purpose of the jumper wire?59874



The whole plug used to go here (circled below in your pic from post 20):
59893

Manuals use the jumper to bypass the connections going to an auto's neutral safety switch.

This chart should help:
http://dmctalk.org/showthread.php?16716-Bulkhead-Connectors-PDF&p=237326#post237326

[CFI]

The whole plug used to go here (circled below in your pic from post 20):
59893

Manuals use the jumper to bypass the connections going to an auto's neutral safety switch.

This chart should help:
http://dmctalk.org/showthread.php?16716-Bulkhead-Connectors-PDF&p=237326#post237326

Thank you. I have the charts but can not find the diagnostic plug in my car. That red connector I’m holding was just sitting there near the bulkhead connectors. I’m guessing something was changed when the car was refurbished. I ended up using the orange wire on the blue bulkhead connector to get FV dwell.

[Bitsyncmaster]

Thank you. I have the charts but can not find the diagnostic plug in my car. That red connector I’m holding was just sitting there near the bulkhead connectors. I’m guessing something was changed when the car was refurbished. I ended up using the orange wire on the blue bulkhead connector to get FV dwell.

Diagnostic connector is down near the ignition distributor but the PO may have removed it. I removed mine since it has no use.

That red connector should have plugged into the red bulkhead connector but I guess the PO changed things.

[Ron]

Thank you. I have the charts but can not find the diagnostic plug in my car. That red connector I’m holding was just sitting there near the bulkhead connectors. I’m guessing something was changed when the car was refurbished. I ended up using the orange wire on the blue bulkhead connector to get FV dwell.

That's where I always get it...

Yeah, it does look like refurb/repairs -- For some reason the link to the pic of your connectors was bad in my post:

59899

[CFI]

Ok I’m back home and running some tests for a second time. I think I may have not had a good ground during the 1.5 volt test the first time, as I got a completely different result this time.

Hot engine:
O2 disconnected, FV dwell: 45 (book range 40-50)
Ground the O2 lead to ECU, dwell: 88 (book min 87)
1.5 volts applied to O2 ECU lead: dwell 12 (book max 20)
Reading from 02 sensor wire: steady at 1.0 (should be about .5 IIRC)

So it seems that my 02 sensor is reading high. I left the volt meter connected for a few minutes and it never really budged from 1.0 volts. Bad sensor?

Actually, now that I think about it the reading is probably correct as it represents a rich mixture. So maybe my mixture needs to be adjusted?

[CFI]

I plugged the O2 sensor in and ran some tests again

Hot engine

O2 volts fluctuating between .35 and .8
FV dwell fluctuating between 24 and 37

Also noticed the strong fuel smell is gone. It had been very strong even when the engine was hot.

I’m baffled. These current numbers look good. Perhaps something that is acting up intermittently.

[Bitsyncmaster]

I plugged the O2 sensor in and ran some tests again

Hot engine

O2 volts fluctuating between .35 and .8
FV dwell fluctuating between 24 and 37

Also noticed the strong fuel smell is gone. It had been very strong even when the engine was hot.

I’m baffled. These current numbers look good. Perhaps something that is acting up intermittently.
Your lambda is working so if the O2 sensor is good you should be OK. Mixture may need a little adjustment to get that dwell a little higher.

[CFI]

Your lambda is working so if the O2 sensor is good you should be OK. Mixture may need a little adjustment to get that dwell a little higher.

I guess I could try a new O2 sensor and see what happens, just in case that is what is acting up. With my luck the old one will be permanently rusted in place. If that doesn’t do it, I’ll have the Volvo guys down the road from me have a go.

[Ron]

Wow that's great info...I have the two plugs, but only one used (in a manual car). I'll have a closer look as I never noticed the different colors.

At least in a manual car, the correct plugs seem to matter. I have done some continuity testing, and found that the throttle enrichment switch plug is normally open, and grounded when the microswitch closes. However, my unused kickdown switch has continuity, even though it's left dangling in the engine bay?!
Both switches should be normally open. On a manual, the kick down switch is not installed (LightGreen/Green and Black wires).
Assuming you disconnected the kick down switch when checking continuity, it's bad. I'd double check which pair of wires it was plugged into and remove it.

[Ron]

I guess I could try a new O2 sensor and see what happens, just in case that is what is acting up. With my luck the old one will be permanently rusted in place. If that doesn’t do it, I’ll have the Volvo guys down the road from me have a go.Arggg...I hate intermittent/mystery problems. ...I'd wait until it starts acting up again before taking it to the Volvo guy$, lol. Good luck!!

[CFI]

Arggg...I hate intermittent/mystery problems. ...I'd wait until it starts acting up again before taking it to the Volvo guy$, lol. Good luck!!

Thanks!

[CFI]

Your lambda is working so if the O2 sensor is good you should be OK. Mixture may need a little adjustment to get that dwell a little higher.

What FV dwell range am I looking for on a hot engine?

[Ron]

It should swing between 35°-45° (use 4 cyl scale!), with the breather installed and the access hole plugged.

More HERE (http://dmctalk.org/showthread.php?12909-How-To-Set-CO-Dwell)

[CFI]

It should swing between 35°-45° (use 4 cyl scale!), with the breather installed and the access hole plugged.

More HERE (http://dmctalk.org/showthread.php?12909-How-To-Set-CO-Dwell)

Awesome, thank you. Some good news: my most recent fill up indicates 20mpg. Still not what it should be but better than the 16 mpg I was getting.

[CFI]

So I’ve been dealing with a wonky idle and poor gas mileage for a while. I tried a few things but it only got worse: the car would stall when going into reverse, and sometimes going into drive! Sometimes it would even stall if I took my foot off the gas quickly while I was driving! (Idle or mixture too low maybe???)

I THINK I may have finally solved it.

In the last few days I’ve:
Cleaned idle motor
Replaced O2 sensor
Adjusted curb screw, idle switch screw, and the brass screws per instructions on another thread
Adjusted the arm that pushes the throttle plates open
Adjusted mixture using dwell readings (it was waaaaaay off)
Ran the Lambda/Dwell tests per the shop manual

The car now idles smoothly, does not hunt for idle cold or hot, does not stall going into any gear, does not stall when I take my foot off the gas quickly, does my taxes, makes me breakfast, and compliments my hair. Gas mileage remains to be seen but I have a good feeling.

Thanks to everyone for their suggestions and encouragement.

Now I shall put down this iPad, get in my car and DRIVE IT:driving1::biggrin:

[David T]

Gas mileage is the ultimate test of how the whole car is running. It is affected by things other than just the motor. Tires, alignment, tire pressure, bad wheel bearings are just a few examples of things that can ruin your gas mileage. Of course if the motor is not set up and running properly, that is the biggest contributor. Always check your gas mileage and know what it is and if you see it change you know something is happening. Make sure your timing is set up right and the vacuum and mechanical advance are working.

[Ron]

Cool beans, AND taders!

[CFI]

I finally got the chance to run a mileage test. I just got back from a 96 mile drive, the vast majority of those miles spent travelling between 55-65 mph. No traffic. I filled up, drove, and didn't stop until I got back to the gas station (ok, maybe one or two red lights, but that's it).

28 MPG!!

I'm so excited! In the year I've owned my car I've never gotten better than 21 or 22 MPG.

Installing a new oxygen sensor and resetting my fuel mixture did the trick.

Thanks to everyone who chimed in with ideas and encouragement.

[Bitsyncmaster]

I finally got the chance to run a mileage test. I just got back from a 96 mile drive, the vast majority of those miles spent travelling between 55-65 mph. No traffic. I filled up, drove, and didn't stop until I got back to the gas station (ok, maybe one or two red lights, but that's it).

28 MPG!!

I'm so excited! In the year I've owned my car I've never gotten better than 21 or 22 MPG.

Installing a new oxygen sensor and resetting my fuel mixture did the trick.

Thanks to everyone who chimed in with ideas and encouragement.

Great. A good running D with 5 speed will get that for highway mileage as long as your mostly in fifth gear.