Idle Mixture Adjustment

[Jonty]

Hi all

I have a Kjet technical question which I hope I can ask as clearly as I can. When the Delorean is at idle I understand that the idle motor controls the amount of air that the engine can draw. The amount of fuel is regulated by the position of the plunger which can be adjusted with the CO 3m screw. What I am trying to work out is that on my car if I remove the CO plug bung my car will either start surging or die completely. My question is if the idle motor controls the volume of air at idle why would removing the CO bung have any bearing on my idle ? I guess a more technical question is to what extent is the air plate “metering” air while the car is at idle with the idle motor operating? Could it be my throttle plates or brass screws are not closed so removing the bung adds more air at idle?

Hopefully this make sense

[Jonty]

Actually I have been thinking about this more and I think I might have answered my own question but want to cross check. Is it the case the while at idle the air plate is not metering any air but it is metering fuel. So if I remove the bung then some air that is being metered by the idle motor is not flowing though the air plate (because it’s flowing through the open mixture screw hole) then the air plate will rise up slightly and restrict the fuel flow (therefore causing a lean condition and in my case killing the engine).

Am I right here?

[Ron]

Hi all

I have a Kjet technical question which I hope I can ask as clearly as I can. When the Delorean is at idle I understand that the idle motor controls the amount of air that the engine can draw. The amount of fuel is regulated by the position of the plunger which can be adjusted with the CO 3m screw. What I am trying to work out is that on my car if I remove the CO plug bung my car will either start surging or die completely. My question is if the idle motor controls the volume of air at idle why would removing the CO bung have any bearing on my idle ? I guess a more technical question is to what extent is the air plate “metering” air while the car is at idle with the idle motor operating? Could it be my throttle plates or brass screws are not closed so removing the bung adds more air at idle?

Hopefully this make sense
Removing the plug allows air to enter the system without it being 'measured' (by the plate). This is why you must plug the hole and allow the engine to run a few seconds when taking a CO/dwell reading.
It is odd that removing the plug makes the engine die. The brass screws may have something to do with that...? Anyway, the brass screws are supposed to be closed on a K-Jet system that utilizes the Idle Air Control system (like a DeLorean).

[Ron]

Actually I have been thinking about this more and I think I might have answered my own question but want to cross check. Is it the case the while at idle the air plate is not metering any air but it is metering fuel. So if I remove the bung then some air that is being metered by the idle motor is not flowing though the air plate (because it’s flowing through the open mixture screw hole) then the air plate will rise up slightly and restrict the fuel flow (therefore causing a lean condition and in my case killing the engine).

Am I right here?Yes.
(FWIW- I never liked the use of "air metering plate" here, often used for some reason. As a verb, "meter" = "measure", especially for the British...The manual calls it an "air sensor plate", which "regulates" fuel ;-)

Air drawn into the engine forces the plate down, which causes the fuel distributor (FD) plunger to raise, increasing fuel flow. Meanwhile, the control pressure (from the CPR/WUR) forces the FD plunger down. The result of these two counteracting forces against the plunger (and the lambda system) determine the fuel flow, idling or not.
At idle, the idle speed ECU rotates the idle speed motor to obtain the correct RPM. The fuel system will react to any change in air it, or,anything else, makes. (Try viewing it as vicious circle where desired results are achieved by setting boundaries and only reacting when one is crossed ;-)
The amount of air entering the system through the adjustment hole would throw things off; but I seriously doubt that alone could cause the engine to die.

Shut the brass screws!
Re-set the timing.
Check the CO/dwell (ALWAYS done last!)
If no luck, check pressures.

[Bitsyncmaster]

Removing or plugging the adjustment hole will make a small change to the idling engine but the working idle system should quickly compensate. That is if everything is adjusted properly. Your mixture adjustment may be far off and a cold engine is not adjusting the mixture dynamically via dwell changing.

1) Is your idle RPM holding at 775 RPM?
2) Is your frequency valve buzzing? It should buzz with a cold or hot engine.

You only want to adjust your mixture on a warmed up engine. That is when the lambda system is working to hold the mixture at 1.00 lambda (14.7 AFR).

[David T]

Removing or plugging the adjustment hole will make a small change to the idling engine but the working idle system should quickly compensate. That is if everything is adjusted properly. Your mixture adjustment may be far off and a cold engine is not adjusting the mixture dynamically via dwell changing.

1) Is your idle RPM holding at 775 RPM?
2) Is your frequency valve buzzing? It should buzz with a cold or hot engine.

You only want to adjust your mixture on a warmed up engine. That is when the lambda system is working to hold the mixture at 1.00 lambda (14.7 AFR).

Not only must the engine be warmed up, every other adjustment MUST have been done (and done correctly) and any worn, old, tired parts should have been replaced. The mixture adjustment is only then able to be set correctly. Never try to adjust away a problem like vacuum leaks, worn spark plugs, dirty fuel injectors etc. A tiny adjustment has great effect and if you don't know what you are doing it is probably better to leave the mixture screw alone, it's probably closer to correct then you will be turning it to. Especially if the tamper proof plug is still there.

[Jonty]

Thanks all

To answer your questions my idle is 775 and is very stable (open loop at least). I always measure on a warmed up engine. My FV is buzzing away and working fine. I have found since day one whenever I remove the mixture bung the engine dies. I had the system tuned with an gas analyser so I was fairly sure the mixture was right. The off thing is that the dwell swings from 45 down to below 20 when in closed loop. I made a very rich adjustment and it simply raises the idle to 1000 and no impact on dwell. All a little odd. It has been fully smoke tested and no leaks. The WUR, idle motor, distributor and fuel pump are all no more than 5 years old.

[Bitsyncmaster]

Thanks all

The off thing is that the dwell swings from 45 down to below 20 when in closed loop. I made a very rich adjustment and it simply raises the idle to 1000 and no impact on dwell.

That is swinging to much if your seeing it swing 45 to 20 up and down. It should be half that or less. Have you replaced the O2 sensor? A very small adjustment normally makes a large dwell change. I have also seen problems setting dwell if the exhaust is restricted (plugged CAT).

[Jonty]

Yes it’s a fairly new O2 sensor. All a bit frustrating. I’m starting to wonder if it might be something like timing or a valve adjustment.

[Bitsyncmaster]

Yes it’s a fairly new O2 sensor. All a bit frustrating. I’m starting to wonder if it might be something like timing or a valve adjustment.

I don't think timing or valve adjustment would stop the ability to adjust dwell.

[Jonty]

Ok thanks - the other issue is that I keep somehow damaging plugs. I seem to have to remove them and clean them up regularly otherwise I get a hard start and some misfiring in occassion

[Ron]

I would expect the plug issues with it set "very rich" or with the readings you now have...

Why raising the RMP with the CO screw doesn't change the dwell is what bugs me.

How did you make adjustments when using a gas analyzer?

[Jonty]

Thanks Ron - it’s all very weird I agree. No I’m not using a gar analyser. I did find this am that the three brass screws needed a half turn each to fully seat. Also it was quite hard to start this am. I plan to pull the plugs tonight and clean them up then there is a mech close by that knows Kjet and has a gas analyser so will get it check by that as that might then tell if my O2 sensor or the lambda system is playing up.

[Bertone80]

Thanks Ron - itÂ’s all very weird I agree. No IÂ’m not using a gar analyser. I did find this am that the three brass screws needed a half turn each to fully seat. Also it was quite hard to start this am. I plan to pull the plugs tonight and clean them up then there is a mech close by that knows Kjet and has a gas analyser so will get it check by that as that might then tell if my O2 sensor or the lambda system is playing up.

I don't know what a gas analyzer is but there is another way to adjust the mixture/idle for the PRV engine. I did it 16 years ago to my B28F before the engine developed a leak of coolant into oil. It not only worked I also took the car to a smog check (California) and passed the check with excellent measurements. The tool I used was an analog voltage meter with an input impedance of 10 meg ohms. I guess you could use a cheap digital meter but it will be harder because digital numbers tend to jump up and down too quickly.

What I did was to measure the voltage of the O2 sensor while I did the adjustment. The objective was to adjust the CO screw to obtain 0.45 volt from the O2 sensor. The voltage will drift between 0.1 and 0.9 volt if the mixture is too lean or too rich. It will be necessary to also adjust the brass idle screw because the idle RPM will fluctuate when the CO screw is tweaked. I was able to obtain a fairly stable 0.45 volt and an idle RPM around 950 for my B28F. I was able to rev up the engine and the voltage would stabilize to 0.45 volt as well. The smog check machine checks CO at idle and at 2500 RPM as well. As long as the voltage stabilizes to 0.45 volt at idle and 2500 RPM the mixture will be optimal and the Lambda system will yield a CO reading near zero.

It is easy to do but the trick is to use a voltage meter with 10 meg ohm impedance at the range of 1.0 volt. The one I used was a HP brand VTVM (solid state although called VTVM). I pick it up from a flea market long long time ago.

[Ron]

...No I’m not using a gar analyser..

I was asking about when you said...


I had the system tuned with an gas analyser so I was fairly sure the mixture was right.

...I was wondering about using the brass screws and/or CO screw, etc.

Anyway, I (we?) was assuming the smoke test eliminated vacuum leaks. But since the screws were open, you found one... So at this point, it looks like: leave them shut, clean the plugs, check the timing, and try setting it with a dwell meter. (You can disable the idle speed control system and set it up with a gas analyser like a Volvo (also in the manual) instead of a D, but why?)
:wrenchin:

[David T]

Large swings indicate 1 or more cylinders not firing properly. Could be spark plugs, bad injector, that kind of thing. To minimize dwell swings you must get every cylinder as balanced (matched) as closely as possible to each other. It starts with a compression test and often involves checking and adjusting the valves.

[Ron]

+1 ...I'm betting on plugs.

[Jonty]

Thanks all - it had a bit of a stutter this morning so you guys may be on to something with the plugs. This will be the third time I’ve had to clean them so something keep messing with them (and it’s not rich which is the usual culprit). Maybe they got damaged at some point

[Jonty]

Ron just picking up on a comment you made about setting up with a gas analyser. Would if not be better to disconnect the FV and set the mixture with a modern gas analyser then simply plug the FV back in again? Would that not set the perfect baseline for the 02 sensor and FV to do its thing? Would that not rule out a dodgy narrow band 02 sensor?

[Bertone80]

If the mixture is already too lean removing the CO adjustment plug can make it even leaner then the idle can no longer hold up but to die. If the mixture is too rich to begin with then removing the plug will cause the idle to surge up and down which can cause the idle to die too when the RPM swings to low and when that is too low. When the mixture is too lean or too rich the engine RPM will drop. This is why removing the plug will cause the engine RPM to fluctuate. usually you will see the idle revs up and down or simply dies.

The correct mixture needs to be set properly before setting the idle by turning the brass screw. You can sniff the exhaust to get an idea if the mixture is right. If the exhaust stinks the mixture is off. Measuring the O2 sensor voltage is the most accurate way to set the mixture properly. Sniffing the exhaust gas is not a good thing to do.

Make sure the vacuum lines are correctly connected and no leak before adjusting the mixture. The mixture has to be right for the idle to be meaningful. The adjustment should only be done when the engine has reached its operating temperature. You can set the idle a little higher then adjust the mixture. Once the mixture is right then turn down the idle to whatever it is supposed to be. I set my B28F with auto transmission to 950 RPM. I set the idle a little higher to prevent overheating when driving in congested city streets.

[Jonty]

Thanks all. Well I’ve done my testing and here is what I found. I clean all the plugs and when in open loop it idles perfectly. I then tested the lambda system by applying 1.5v across it and then grounding it and that all works (it goes to each end of the dwell range). Now here what is odd. I tested the O2 signal on a mv scale and it’s basically sitting at a fixed voltage. When I tested it (engine all warmed up) it was 450mv static. When I increase rpm it would slowly increase mv up to 800mv but when I let it idle again it would stay static at that mv level then very slowly come down. Isn’t the O2 sensor supposed to swing voltage quite fast? If so that may be the issue as the lambda system is trying compensate. Am I on right track?

[Bitsyncmaster]

Yes the O2 sensor responds to mixture changes very fast. The narrow band sensor just looks for any oxygen or not. So the lambda ECU is making the mixture richer if that O2 sensor voltage is above 0.45 volts or leaner if below.

Using voltage to adjust your mixture really does not zero in the mixture adjustment because the lambda system will keep that O2 sensor voltage holding by changing the mixture via dwell changing. The same goes for checking with a wide band sensor on the exhaust. You want to zero in on the dwell number so your starting and wide open throttle mixtures are set to intended values. Remember the O2 sensor takes time to warm up and produce voltage even with a hot engine.

[Jonty]

Thanks Dave - sorry just to be clear do I have a faulty o2 sensor based on my results? I wasn’t trying to set the mixture taking a direct voltage reading off the sensor I was just trying to see if the sensor was working. I recall testing the sensor last year and it would show rapid voltage changes on my digital gauge but now it’s very sluggish and mostly shows a static voltage with slow Increases and decreases when I change rpm.

[Ron]

Ron just picking up on a comment you made about setting up with a gas analyser. Would if not be better to disconnect the FV and set the mixture with a modern gas analyser then simply plug the FV back in again? Would that not set the perfect baseline for the 02 sensor and FV to do its thing? Would that not rule out a dodgy narrow band 02 sensor?I've never found the need to on a D, but if using a gas analyser, you would want to disconnect the O2 sensor (not the FV). And then you would potentially be left with the brass screw(s) open...


Thanks all. Well I’ve done my testing and here is what I found. I clean all the plugs and when in open loop it idles perfectly. I then tested the lambda system by applying 1.5v across it and then grounding it and that all works (it goes to each end of the dwell range). Now here what is odd. I tested the O2 signal on a mv scale and it’s basically sitting at a fixed voltage. When I tested it (engine all warmed up) it was 450mv static. When I increase rpm it would slowly increase mv up to 800mv but when I let it idle again it would stay static at that mv level then very slowly come down. Isn’t the O2 sensor supposed to swing voltage quite fast? If so that may be the issue as the lambda system is trying compensate. Am I on right track?
300 milliseconds is typical.
The O2 sensor maybe sooted too.

Does "all that" mean these:
63743

I'm guessing not "A". :smile:

And "full range" = 20° (1.5v) to 87° (grounded)?
What was the dwell with everything in place??

[Jonty]

Hi Ron

All the tests in the manual for the lambda system check out. Applying 1.5v I get a constant 87. Grounding the system I get a constant 12. Applying full WOT I get 54. What I can’t get right is with the 02 plugged in a closed loop dwell swinging between 45 and 35. I disconnected the O2 sensor and measure the mv coming off the sensor on a fully warm engine and it was pretty much static at 450mv. If I revved the engine it would slowly climb up to about 750mv but when I brought the engine back to idle it would hold 700mv the very slowly start coming down. On that basis is my O2 sensor faulty or not?

When I plugged the O2 sensor back in the dwell just sat at 45. This is incredibly frustrating so I’m hoping it’s just a faulty 02 because I’ve nothing else to check!

[Ron]

Sounds like it to me -- Sooty O2 sensors have slow reaction times.

Hang in there!

[Jonty]

Great thanks Ron. This process can certainly add to the grey hairs but luckily kind people like yourself can help narrow down! Cheers

[Ron]

You're welcome! Hopefully that will do it. (I'd probably get plugs too tho...)

They can't screw with my hair's color anymore. However I do have an occasional problem with temptations to pull it.

[David T]

To use a gas analyzer you need the hose adapter hook-up per the procedure on D:04:01. The Workshop Manual actually doesn't use the dwell meter to set the mixture, it is only used to confirm the Lambda system is operating. With that said you can set the mixture very well using just a dwell meter if everything is working correctly. You are not supposed to measure the exhaust at the tailpipe, the adapter taps off ahead of the catalytic converter.

[Bertone80]

The Lambda controller constantly adjusts the mixture through the frequency valve. The mixture will swing back and forth between too rich and too lean constantly too. As a result the O2 sensor voltage will swing back and forth between 0.1 and 0.9 volt accordingly as well. Most, if not all, digital volt meters will read and display peak voltage so it is not usable for monitoring how the Lambda system works. What's needed is a volt meter that gives the average voltage it sees. That's why I used an analog meter to measure the sensor voltage. Analog meter displays average value the meter sees. If it shows 0.45 volt it says the mixture is controlled right on target swinging between rich and lean with an average right in the middle.

I remember I disconnected the O2 sensor when I did the measurement while tweaking the mixture adjustment screw. I guess that was not right because the Lambda controller might try to correct the mixture in an extreme manner. I will soon do another round of adjustment for my B28F. I will do it with the O2 sensor connected.

My Bertone was able to pass California smog test in 2004 with excellent numbers. I remember the test technician told me that he was surprised that such an old brick passed so well.

[Bertone80]

By the way, I remember trying to adjust the mixture to achieve fastest Idle RPM (meaning max power). That will give a bad emission as the exhaust really stinks. When the mixture is set to minimize CO emission the idle RPM will be actually lowered a little. This indicates that the emission system does have an impact on the gas mileage.

[Jonty]

To use a gas analyzer you need the hose adapter hook-up per the procedure on D:04:01. The Workshop Manual actually doesn't use the dwell meter to set the mixture, it is only used to confirm the Lambda system is operating. With that said you can set the mixture very well using just a dwell meter if everything is working correctly. You are not supposed to measure the exhaust at the tailpipe, the adapter taps off ahead of the catalytic converter.

Thanks David I didn’t realise that. I’m getting very frustrated with this system as I’ve had issues since day one getting the right dwell. I really want to get a gas analyser to confirm mixture so that at least the mixture is right and I can then go and try figure out what’s causing the weird dwell behaviour. I’ll also do a valve adjustment and compression test as well as new plugs and 02 sensor. If that all doesn’t work I give up.

[Ron]

To use a gas analyzer you need the hose adapter hook-up per the procedure on D:04:01. The Workshop Manual actually doesn't use the dwell meter to set the mixture, it is only used to confirm the Lambda system is operating. With that said you can set the mixture very well using just a dwell meter if everything is working correctly. You are not supposed to measure the exhaust at the tailpipe, the adapter taps off ahead of the catalytic converter.+1!

I can see using the analyser on the PRVs w/o an idle speed system. But I don't see hooking it up, setting the RPM with the common brass screw, then shut it. Granted, the manual says it will "usually be shut" when you're done. (The ISM would compensate anyway...) But, I'm not going to leave it open contrary to the idle circuit requirements it gives (It's a 1980 version of cut and paste from Volvo manuals.) Nothing will have changed and the next step calls for hooking up a dwell meter.
:dunno:

[Ron]

The Lambda controller constantly adjusts the mixture through the frequency valve. The mixture will swing back and forth between too rich and too lean constantly too. As a result the O2 sensor voltage will swing back and forth between 0.1 and 0.9 volt accordingly as well. Most, if not all, digital volt meters will read and display peak voltage so it is not usable for monitoring how the Lambda system works. What's needed is a volt meter that gives the average voltage it sees. That's why I used an analog meter to measure the sensor voltage. Analog meter displays average value the meter sees. If it shows 0.45 volt it says the mixture is controlled right on target swinging between rich and lean with an average right in the middle.

I remember I disconnected the O2 sensor when I did the measurement while tweaking the mixture adjustment screw. I guess that was not right because the Lambda controller might try to correct the mixture in an extreme manner. I will soon do another round of adjustment for my B28F. I will do it with the O2 sensor connected.

My Bertone was able to pass California smog test in 2004 with excellent numbers. I remember the test technician told me that he was surprised that such an old brick passed so well.I'm with you on the O2 sensor since disconnecting it would set the dwell to a constant ~45°.
(Although only off 5°, I wanna watch it in action;-)

[Jonty]

+1!

I can see using the analyser on the PRVs w/o an idle speed system. But I don't see hooking it up, setting the RPM with the common brass screw, then shut it. Granted, the manual says it will "usually be shut" when you're done. (The ISM would compensate anyway...) But, I'm not going to leave it open contrary to the idle circuit requirements it gives (It's a 1980 version of cut and paste from Volvo manuals.) Nothing will have changed and the next step calls for hooking up a dwell meter.
:dunno:

Ron I’m a bit confused about what the issue is plugging in a gas analyser if there is an idle system and what the brass screw has anything to do with it? If the 02 sensor is remove surely the lambda system runs a fixed duty cycle so if I set the AFR with an analyser then plug the o2 sensor back should this have not set the mixture correctly?

[Ron]

Ron I’m a bit confused about what the issue is plugging in a gas analyser if there is an idle system and what the brass screw has anything to do with it? If the 02 sensor is remove surely the lambda system runs a fixed duty cycle so if I set the AFR with an analyser then plug the o2 sensor back should this have not set the mixture correctly?
Sorry, I think things got off track/scattered when I was asking about actually using an analyser or not, and the procedures if you were. Anyway, I've reread everything and hopefully I can bring it all together-

If I'm following your situation it seems like a waste of time and effort. We can measure the voltage, as Bertone80 did; use an analyser, as in the manual (but not a procedure that leaves all of the brass screws 1/2 turn open); or the chart/dwell, which it says to confirm with anyway. Using dwell is the only way that measures when things are as they will be during normal operation. (The O2 sensor is connected, the RPM is not jacked up to 950, and the brass screw is not allowing air behind the throttle plates...)
The thing about having an idle system is that I understand that the procedures using an analyser were laid out before they were used on a PRV. In short, they have you adjusting the fuel when there is a system added afterwards that can vary the air... (Which may not really matter if everything is functioning properly.)
Yes, using an analyser and unplugging the O2 sensor forces the dwell somewhere between 40° & 50°. If it happens to be 40° (probably not), that part is ok (except it's not normal for it to be static). If not, and especially if it happens to be 50°, you'll probably be readjusting it using dwell after confirming with the pulse chart...
However it is done, we're looking for why a very rich adjustment simply raises the idle to 1000 with no impact on dwell. According to the dwell readings, a bad O2 sensor fits...the other methods would indicate the same.

Back to the brass screws- Since you found yours were open some, once you get the dwell to respond correctly, I can see using the correct type of analyser (as David mentioned) to balance the banks. (And give you peace of mind ;-).

EDIT: Anxiously awaiting a report after the new sensor (and plugs?) is installed and the fate of our hair...

[Jonty]

Sorry, I think things got off track/scattered when I was asking about actually using an analyser or not, and the procedures if you were. Anyway, I've reread everything and hopefully I can bring it all together-

If I'm following your situation it seems like a waste of time and effort. We can measure the voltage, as Bertone80 did; use an analyser, as in the manual (but not a procedure that leaves all of the brass screws 1/2 turn open); or the chart/dwell, which it says to confirm with anyway. Using dwell is the only way that measures when things are as they will be during normal operation. (The O2 sensor is connected, the RPM is not jacked up to 950, and the brass screw is not allowing air behind the throttle plates...)
The thing about having an idle system is that I understand that the procedures using an analyser were laid out before they were used on a PRV. In short, they have you adjusting the fuel when there is a system added afterwards that can vary the air... (Which may not really matter if everything is functioning properly.)
Yes, using an analyser and unplugging the O2 sensor forces the dwell somewhere between 40° & 50°. If it happens to be 40° (probably not), that part is ok (except it's not normal for it to be static). If not, and especially if it happens to be 50°, you'll probably be readjusting it using dwell after confirming with the pulse chart...
However it is done, we're looking for why a very rich adjustment simply raises the idle to 1000 with no impact on dwell. According to the dwell readings, a bad O2 sensor fits...the other methods would indicate the same.

Back to the brass screws- Since you found yours were open some, once you get the dwell to respond correctly, I can see using the correct type of analyser (as David mentioned) to balance the banks. (And give you peace of mind ;-).

EDIT: Anxiously awaiting a report after the new sensor (and plugs?) is installed and the fate of our hair...

Thanks Ron that's really helpful appreciate you taking the time. By way of update the car developed a misfire today so I can now add that to the list. Just to summarise all in one place and what I plan to do:

Current state of car:

1. all fuel system parts are not older than 5 years (including WUR, distributor, accumulator, injectors and DMCH pump)
2. car now misfires
3. FV works
4. Lambda system checks all looked fine (89 grounded, 12 with 1.5v applied and 53 with WOT switch engaged)
5. Car takes a long to time to closed loop and sometimes not at all. When it does it has a wild dwell swing sometime between 45 and less than 20
6. When measuring current O2 sensor the voltage change is quite slow
7. Car takes 3 to 4 seconds of cranking to start when cold and after it has been left for more than 5 hours (hot start after an hour is ok or if I start it cold it and shut down instantly it will fire back up straight away)
8. CSV works fine (and have Dave's hot start relay)

What I will do next:

1. Have a compression test and timing test today
2. Will do valve adjustment later this week
3. Will replace spark plugs when they arrive
4. Will replace o2 sensor
5. Will do fuel pressure check
6. Another smoke test
6. Will pray to the kjet gods...

Thanks

[Bitsyncmaster]

Thanks Ron that's really helpful appreciate you taking the time. By way of update the car developed a misfire today so I can now add that to the list. Just to summarise all in one place and what I plan to do:

Current state of car:

1. all fuel system parts are not older than 5 years (including WUR, distributor, accumulator, injectors and DMCH pump)
2. car now misfires
3. FV works
4. Lambda system checks all looked fine (89 grounded, 12 with 1.5v applied and 53 with WOT switch engaged)
5. Car takes a long to time to closed loop and sometimes not at all. When it does it has a wild dwell swing sometime between 45 and less than 20
6. When measuring current O2 sensor the voltage change is quite slow
7. Car takes 3 to 4 seconds of cranking to start when cold and after it has been left for more than 5 hours (hot start after an hour is ok or if I start it cold it and shut down instantly it will fire back up straight away)
8. CSV works fine (and have Dave's hot start relay)

What I will do next:

1. Have a compression test and timing test today
2. Will do valve adjustment later this week
3. Will replace spark plugs when they arrive
4. Will replace o2 sensor
5. Will do fuel pressure check
6. Another smoke test
6. Will pray to the kjet gods...

Thanks

My guess is your O2 sensor is bad. It should go closed loop in 2 to 3 minuets.

[Jonty]

My guess is your O2 sensor is bad. It should go closed loop in 2 to 3 minuets.

Thanks - question is it better to run it without the O2 sensor plugged in if it’s bad until I get a new one? Just in case it’s causing mischief?

[Bitsyncmaster]

Thanks - question is it better to run it without the O2 sensor plugged in if it’s bad until I get a new one? Just in case it’s causing mischief?

Some people run without it plugged in mostly to stop idle hunting. If you do that you probably won't pass emission testing and expect less MPG.

[Jonty]

Some people run without it plugged in mostly to stop idle hunting. If you do that you probably won't pass emission testing and expect less MPG.

No problem - no emission testing where I live ;)

[Jonty]

Hi all

Just wanted to update you and all say thanks. I'm part way to a solution. My misfire was really bad today but limited to a local mech and ran a compression test. Result were:

155 - 1
145 - 2
150 - 3
155 - 4
155 - 5
155 - 6

So will take that as a pass (the mech was pretty happy with results). As part of doing that we check the plus and they looked all fine but when we started it it was clear it was only running 5 cylinders. We pulled the leads and noticed no reaction with cylinder 2 and discovered the lead must be dodgy. After wiggling it round a bit the cylinder came back to life and it drove perfectly home. Looks like I need to invest in some new leads. Does anyone know if I can change this without removing the manifold?

So next steps are to check dwell tonight and if that is till a bit wired then i will replace the o2 sensor when it arrived (which i will probably do anyway).

Thanks

[Jonty]

Hi all

Further update I’ve now tested dwell and it’s going closed loop and swinging between 35 and 25. My mixture bung has got stuck so when I free that up I can test giving it a slight tweak to richen up and see if that works. One other question, the one residual issue is that it takes the car 3 or 4 seconds of cranking to start warm or cold. The CSV is fine and the accumulator is fine so it’s not a “hot start” issue. What I find is if I start it cold then quickly shut off (so it’s still cold) it will fire straight away which makes me think it’s a fuel supply issue.

[Ron]

COOL!
Sounds like your O2 sensor is cleaning up. (Damn screws ;-)

Several ways to change the plug wires HERE (http://dmctalk.org/showthread.php?10006-Spark-plugs-wires-help). I'd do the cap and rotor while I was in there.

The hard start may go away after you put some miles on it. If not, the gauges are on the way...

[Jonty]

Thanks Ron! I did shut down and start it after 10 mins and it never went closed loop so I think the 02 sensor still stuffed but a new one not far away! Have just ordered new spark plug leads. I’m pretty sure I’m only a tire away from having replaced every bloody part in this car 😂

[Ron]

NP!

lol - The spare?

Just curious- With smoothness in mind only, does it idle perfectly in open loop now as in post 21 or significantly better?

[Jonty]

Yes it idles really well in open loop (pretty much the same as always). It was idle well in closed loop after I got home but never went back to closed loop after I started it again. I’m fairly sure it must be the 02 sensor and I’ve got a new one ordered. The misfire seems to be an unrelated issue due to the plug lead. I’ve also just ordered the cap and rotor as per your recommendation

[Jonty]

Hi all just wanted to close off this thread by saying all issues now fixed and perfect dwell readings. The main issue was a worn distributor cap and a dodgy spark plug lead. I also replaced the o2 sensor and everything fell back into place.

Thanks