How to remove Idle mixture plug?

[Alexander]

Hi all,

I want to drill out the plug so I can acces the idle mixture screw.
Can this be safely done without dismantling? Or do I need to remove the assembly and drill from the inside? Any recommendations?
PS: this is my first thread, just got my DeLorean!

69083

[82DMC12]

Hi all,

I want to drill out the plug so I can acces the idle mixture screw.
Can this be safely done without dismantling? Or do I need to remove the assembly and drill from the inside? Any recommendations?
PS: this is my first thread, just got my DeLorean!

69083

Don't drill it out. Lever it out from underneath. remove the mixture control unit and open it up, then you can use the seesaw inside to lever the plug up and out without damage or metal shavings.

[Alexander]

Don't drill it out. Lever it out from underneath. remove the mixture control unit and open it up, then you can use the seesaw inside to lever the plug up and out without damage or metal shavings.

Thanks! And while we are here, what is the optimal CO reading while idling after warm up? I am using a digital meter that reads out directly in %CO

[David T]

Unless you have the proper equipment and it is recently calibrated, You probably won't be able to adjust the mixture any better than it already is. Besides, it is a VERY sensitive adjustment and if it is off, you would hardly have to move the screw, that is how sensitive it is. If the mixture is off the more likely cause would be air leakage or worn tune-up parts (ignition wires, spark plugs, Cap, rotor) or dirty fuel injectors. Rarely can you "fix" a problem by adjusting that mixture screw. Congrats on getting your Delorean.

[Alexander]

Unless you have the proper equipment and it is recently calibrated, You probably won't be able to adjust the mixture any better than it already is. Besides, it is a VERY sensitive adjustment and if it is off, you would hardly have to move the screw, that is how sensitive it is. If the mixture is off the more likely cause would be air leakage or worn tune-up parts (ignition wires, spark plugs, Cap, rotor) or dirty fuel injectors. Rarely can you "fix" a problem by adjusting that mixture screw. Congrats on getting your Delorean.

I realise that it s very sensitive. The recommendation to work on the idle mixture comes from Delorean in europe. I had some interactions with them and they came to this conclusion. FYI: the tests show 0.7% CO. I thought I read somewhere it should be 2%, but I am not sure...

[Bitsyncmaster]

You adjust mixture via reading dwell from the lambda ECU. You need to center that reading so the system keeps it adjusted correctly as things change. (altitude, fuel, temp etc). Checking CO after adjusting the dwell can tell you that something else is wrong. The O2 sensor keeps the mixture fixed at 14.7 AFR as long as your lambda system is centered and working.

[David T]

You adjust mixture via reading dwell from the lambda ECU. You need to center that reading so the system keeps it adjusted correctly as things change. (altitude, fuel, temp etc). Checking CO after adjusting the dwell can tell you that something else is wrong. The O2 sensor keeps the mixture fixed at 14.7 AFR as long as your lambda system is centered and working.

The "proper" way is to adjust the mixture by measuring tailpipe emissions with an exhaust gas analyzer. That way you can measure CO, HC and NOX. Using the duty cycle of the frequency valve is a short-cut because you are only measuring O2. Gets you close but the mixture screw is already closer than you can get by using just a dwell meter if it has never been touched. If the mixture is "off", the way to fix it is not to try to adjust it but to find the cause. The only time you need to actually adjust the mixture screw is if the mixture unit has been replaced or rebuilt. If it is original to the car and still has the tamper-proof plug, it should not need to be adjusted.

[Bitsyncmaster]

The "proper" way is to adjust the mixture by measuring tailpipe emissions with an exhaust gas analyzer. That way you can measure CO, HC and NOX. Using the duty cycle of the frequency valve is a short-cut because you are only measuring O2. Gets you close but the mixture screw is already closer than you can get by using just a dwell meter if it has never been touched. If the mixture is "off", the way to fix it is not to try to adjust it but to find the cause. The only time you need to actually adjust the mixture screw is if the mixture unit has been replaced or rebuilt. If it is original to the car and still has the tamper-proof plug, it should not need to be adjusted.

With a working lambda system,

How do adjust for CO?
Now how do adjust for HC?
Now how do adjust for NOX?

What three or more things are controlling those?

[David T]

With a working lambda system,

How do adjust for CO?
Now how do adjust for HC?
Now how do adjust for NOX?

What three or more things are controlling those?

You adjust for HC (HydroCarbons) with the mixture screw. If that doesn't get the other values into the proper spec you need to find and fix the problem that causes it to be "out of spec". Could be one cylinder is misfiring, the timing is off, a minor vacuum leak, or even a stuck thermostat. Another reason to ONLY touch that mixture screw when you KNOW everything else is perfect.

[Bitsyncmaster]

You adjust for HC (HydroCarbons) with the mixture screw. If that doesn't get the other values into the proper spec you need to find and fix the problem that causes it to be "out of spec". Could be one cylinder is misfiring, the timing is off, a minor vacuum leak, or even a stuck thermostat. Another reason to ONLY touch that mixture screw when you KNOW everything else is perfect.

You don't really adjust mixture with a working lambda. The lambda holds a fixed mixture of 14.7 AFR. When you adjust the "mixture" screw, your centering the lambda system. Now it would adjust mixture if your lambda is not working.

You need a wideband system to adjust mixture.

[David T]

You don't really adjust mixture with a working lambda. The lambda holds a fixed mixture of 14.7 AFR. When you adjust the "mixture" screw, your centering the lambda system. Now it would adjust mixture if your lambda is not working.

You need a wideband system to adjust mixture.

Or an exhaust gas analyzer. When you adjust the mixture screw you are adding and removing HC which affects the amount of O2 that the Oxygen sensor is reading which then adjusts the Frequency valve duty cycle to give more or less fuel to try to hold 14.7-1. Anyway adjusting the mixture screw by using the O2 sensor is an easy way to get very close. My main point is, if the mixture screw has not been disturbed, you aren't going to get it any better by using the duty cycle method. I say hook up a dwell meter to it and see what it is. If it isn't right then BEFORE you go messing with the adjustment, get everything else working perfectly. That mixture screw should be the LAST thing you do, not the first.

[Alexander]

time to add some more info I guess. The problem I have is a 'pumping' idle during warm-up. It varies at a frequency of about once every 1-2 seconds between 750 and 1000rpm. During warm up, as far as I know, there is no lambda correction active. I checked the idle valve (perfectly OK) , even replaced it with another one and the issue is the same. No vacuum leaks neither. I am new to this engine so I don't know what else the ECU is looking at and how it's controlling the idle rpm. The Delorean people in Europe suspect a wrong ATF mix. I have an exhaust analyser and it shows 5% CO, while the workshop manual recommends 1% +/- 0.3%. So for one reason or the other the idle mix is way too rich. Whether that causes the pumping or not I don't know (Delorean says it does). If that gives any more ideas, glad to read them. Thanks for all the replies! Great to feel supported, I don't know anyone else over here in Belgium who has a Delorean.

[David T]

You can't adjust the idle while it is cold or warming up. All tests and adjustments need to be done once the motor is warmed up unless you have a warm-up problem. A hunting (pumping) idle during warm-up is normal but it should not be hunting quite as much as you say. To get a smooth idle everything must be all set up very well. If one cylinder is not firing right the motor will slow down and then speed up after it comes to the next cylinder. To get all of the cylinders to fire equally all of them must be set up identically. The closer you can get them to each other the smoother the idle will be. Start with checking each cylinder's compression. If they are not all within 5% of each other you will never get a smooth idle. All of the valves must be adjusted. All of the spark plugs must be adjusted. All of the fuel injectors must open at the same pressure and all must have a good pattern. Because you have a high CO we can assume one (or more) cylinder(s) is not firing right. One test is to remove an ignition wire from a spark plug one-at-a-time and see which cylinder drops the least. That would be the one misfiring. Or, if you have an IR thermometer, you can check the temperature of each cylinder at the exhaust manifold. The one that is cooler than the others is the misfiring one. A good overall check of the health of the motor and it's systems is to monitor the miles (KM) per gallon (Liter). If you see it is high or going up you know something is not right. You should be getting around 25 MPG or better depending on the kind of driving you do (city or highway) and if it is an auto or a 5-speed (the 5-speed does a little better). Adjusting the mixture screw affects ALL of the cylinders so it can't fix anything if one cylinder is misfiring and giving you a high CO.

[Alexander]

Don't drill it out. Lever it out from underneath. remove the mixture control unit and open it up, then you can use the seesaw inside to lever the plug up and out without damage or metal shavings.

Hi Andy,

I have taken the unit off the engine, but I am not sure what you mean by driving the plug out with the seesaw. The seesaw is actually obstructing acces to the plug from the inside. If you have some additional tips to make me understand...
Thanks
Alexander

[rjd2]

alexander-oddly enough, I am restoring a car currently that had the plug still inserted. I removed it yesterday. here's how I did it: I clamped a vice grip to the shaft of a 2mm alan wrench, and gently tapped it out from the inside with a hammer. I tried the "seesaw as lever" technique briefly, but didnt like how it felt, so I switched to this. came right out. just be careful to not cause any abrasions on the inside of the top half of the MCU.

[Alexander]

alexander-oddly enough, I am restoring a car currently that had the plug still inserted. I removed it yesterday. here's how I did it: I clamped a vice grip to the shaft of a 2mm alan wrench, and gently tapped it out from the inside with a hammer. I tried the "seesaw as lever" technique briefly, but didnt like how it felt, so I switched to this. came right out. just be careful to not cause any abrasions on the inside of the top half of the MCU.

Thanks! so you slipped the vice grip under the seesaw?

[rjd2]

Thanks! so you slipped the vice grip under the seesaw?


no. i took the top half of the MCU and flipped it upside down. i use an old bathmat on my work bench for uses like this, so i dont ding up the top. you can look under the seesaw, and see the hole the plug is seated in from the inside. a 2mm alan wrench, pointed at the hole, was just small enough to fit inside, but its narrow quarters. you cant hold it to push it out. so i clamped a needle nose vice grip to the "L" portion of the alan wrench, and seated the tip of the alan wrench against the plug, and tapped it out with a hammer. just go slow and dont wail on it, it should come right out after 8-10 taps.

[Alexander]

no. i took the top half of the MCU and flipped it upside down. i use an old bathmat on my work bench for uses like this, so i dont ding up the top. you can look under the seesaw, and see the hole the plug is seated in from the inside. a 2mm alan wrench, pointed at the hole, was just small enough to fit inside, but its narrow quarters. you cant hold it to push it out. so i clamped a needle nose vice grip to the "L" portion of the alan wrench, and seated the tip of the alan wrench against the plug, and tapped it out with a hammer. just go slow and dont wail on it, it should come right out after 8-10 taps.

The forum was down yesterday so I could not read your reply in time. In the meantime I worked out an alternative, one without the risk of metal particles in the engine and it can be done without dismantling anything (should have known earlier...).
I drilled a 2.5mm (I am in Europe , so metric...) hole in the plug but not completely through. It's easy to know when to stop because the bottom of the plug has a much harder metal disk. Then a tapped it with a 3mm thread. Turn an allen bold in it with a 3mm nut (yellow) and an oversized 4 or 5 mm nut (red). Holding the bold with a wrench while turning the 3mm nut will pull the plug out. Voila!

[rjd2]

Cool! Replying here, as these threads eventually archive, and can provide help for someone in the future. I was advised that the plugs themselves are rare, and should be preserved. In essence, they can be pushed out from the inside(you found a way to pull it out). any probe that is long and metal and reaches it, can be used to tap it out from the inside.

[Alexander]

I can report back on the original problem I wanted to solve : idle hunting about every second.
Just as Delorean Europe recommended, leaning out the idle mixture did the trick. Turning the mixture screw CCW 1/8th of a turn step by step solved the problem. I needed just short of 1/2 turn. I checked the CO, O2 etc and they are still not in line with the recommendations . CO is too low (0.2 and should be between .5 and 2%) . But the engine now starts and idle's beautifully at around 800rpm. A friend gave me the idle tune procedure for a Renault with the same engine , and that called for touching the 3 big inclined set screws ahead of the idle unit. I may work on these too, and that may bring the CO and O2 levels to the correct values. The system is very sensitive. 1/8th too rich (CW) and the engine stalls and refuses to start again.

[Bitsyncmaster]

I can report back on the original problem I wanted to solve : idle hunting about every second.
Just as Delorean Europe recommended, leaning out the idle mixture did the trick. Turning the mixture screw CCW 1/8th of a turn step by step solved the problem. I needed just short of 1/2 turn. I checked the CO, O2 etc and they are still not in line with the recommendations . CO is too low (0.2 and should be between .5 and 2%) . But the engine now starts and idle's beautifully at around 800rpm. A friend gave me the idle tune procedure for a Renault with the same engine , and that called for touching the 3 big inclined set screws ahead of the idle unit. I may work on these too, and that may bring the CO and O2 levels to the correct values. The system is very sensitive. 1/8th too rich (CW) and the engine stalls and refuses to start again.

You eliminated the closed loop mixture control doing that. You can just unplug your O2 sensor and then adjust the mixture via the mixture screw. Now you would have correct mixture at that idle speed, engine temp, altitude and engine load.

[Rich]

A friend gave me the idle tune procedure for a Renault with the same engine , and that called for touching the 3 big inclined set screws ahead of the idle unit. I may work on these too, and that may bring the CO and O2 levels to the correct values. The system is very sensitive. 1/8th too rich (CW) and the engine stalls and refuses to start again.

Yes, the CO adjustment screw is very sensitive.

Be sure to seal/plug the CO screw access hole after each small adjustment before judging the idle CO and idle smoothness. Remove the hex wrench and plug the hole after each adjustment, only then judge the idle quality or CO level.

No, do not open/adjust the big inclined 3 hex screws. I think they are not used for this system except as plugs. They are to be left as they were from the factory, at least on this engine. None of the K-Jetronic/Lambda info in the
DMC books points to these screws as adjustable. Your friend's Renault PRV motor may be set up differently from a DMC motor in that respect.

[Alexander]

You eliminated the closed loop mixture control doing that. You can just unplug your O2 sensor and then adjust the mixture via the mixture screw. Now you would have correct mixture at that idle speed, engine temp, altitude and engine load.

Are you sure? I am tuning the COLD start idle, as far as I know this is BEFORE the O2 sensor gets in?

[Ron]

+1 Rich

"These adjustment screws are not used on the De Lorean since an electronic idle speed control system is used."
(WSM, D:01:13)

[Bitsyncmaster]

Are you sure? I am tuning the COLD start idle, as far as I know this is BEFORE the O2 sensor gets in?

You said mixture screw so I'm assuming the one you adjust to set the dwell reading. Can you get a photo of the screw you are turning?

[David T]

Those 3 screws are to be left lightly seated closed. The only time you touch them is according to the procedure in the Workshop Manual. Turing the mixture screw the way you did is not the best way to try to set it optimally. As you adjust that mixture screw the idle motor and the Frequency valve are trying to keep the mixture and speed within a certain spec. Tuning by ear is NOT the way to get it right. Close but not right. As you learned, that mixture screw is VERY sensitive. BTW, measuring at the tailpipe is not the way to measure either. You are supposed to use a special tool (basically some hoses) hooked up to the 2 plugs on the exhaust pipes BEFORE the catalytic convertor. If you are going to do this try to follow the procedure in the Workshop Manual.

[Alexander]

You said mixture screw so I'm assuming the one you adjust to set the dwell reading. Can you get a photo of the screw you are turning?

the one hidden under the plug I removed, regulating how high/low the plunger in de fuel distributor sits at idle. see pictures at the beginning of this thread

[Alexander]

Those 3 screws are to be left lightly seated closed. The only time you touch them is according to the procedure in the Workshop Manual. Turing the mixture screw the way you did is not the best way to try to set it optimally. As you adjust that mixture screw the idle motor and the Frequency valve are trying to keep the mixture and speed within a certain spec. Tuning by ear is NOT the way to get it right. Close but not right. As you learned, that mixture screw is VERY sensitive. BTW, measuring at the tailpipe is not the way to measure either. You are supposed to use a special tool (basically some hoses) hooked up to the 2 plugs on the exhaust pipes BEFORE the catalytic convertor. If you are going to do this try to follow the procedure in the Workshop Manual.

Tnx David for your reply. I just got my car, so I am discovering the engine step by step. So I tackle problems and test out stuff, after a while I get a better understanding how the 'system' works and can make a better judgement about what is needed to get as close as possible to the 'best' tuning.
This is literally the first problem visible, because it occurs at cold start. So it's logical I start with that in search for optimisation. I know about the twin pipes (I have and read the manual). What I did was quick and dirty set-up only, and I got an already much better running engine now. You may be surprised, but I bought the Delorean to convert it to EV. The engine/gearbox/wiring will go out soon. But I am enough of a petrolhead and mechanic such that I could not resist the temptation to work on the problem ;-)

[David T]

I understand now what you are trying to accomplish. If you are planning to sell the drivetrain, it is smart to try to get it to run as well as you can. Take some video of it running and driving to help sell it later. It is good to get the car running as well as you can so when you do convert it you have some idea of how it drove and handled BEFORE you converted it.

[Bitsyncmaster]

the one hidden under the plug I removed, regulating how high/low the plunger in de fuel distributor sits at idle. see pictures at the beginning of this thread

So what you did was what I thought. You set the mixture so rich and shut down the lambda closed loop operation. That stopped your hunting and the engine really idle good with a very rich mixture. You would probably not like to drive it that rich. You will probably kill your CAT and O2 sensor and get very poor MPG.

If that hunting is really bothering you then it's better to shut down the lambda by pulling the wire off the O2 sensor. Then you can adjust the mixture screw to set your mixture on the warmed up engine. You would need to set it via a tail pipe wideband or other method since the normal dwell reading will not change.

[Alexander]

So what you did was what I thought. You set the mixture so rich and shut down the lambda closed loop operation. That stopped your hunting and the engine really idle good with a very rich mixture. You would probably not like to drive it that rich. You will probably kill your CAT and O2 sensor and get very poor MPG.

If that hunting is really bothering you then it's better to shut down the lambda by pulling the wire off the O2 sensor. Then you can adjust the mixture screw to set your mixture on the warmed up engine. You would need to set it via a tail pipe wideband or other method since the normal dwell reading will not change.

Thanks once more for your analysis. The weird thing however is that I did nog have to enrich but lean out the idle mixture (turning the mixture-screw CCW) to get rid of the idle hunting during warm up. Hunting in control loops often means that there is too long a delay between the output measurement (O2 sensor) and the correcting feedback into the system (idle valve). Where that would come from I don't know. Delorean guided me at checking if the injectors are working according to specs.