Engine won’t lean out

[Jonty]

Hi all

I have an issue where my delorean will simply not lean out. It is running so rich it keeps fouling the plugs. It is plugged into an external oxygen sensor and no matter how much the mixture screw is adjusted it keeps running rich and won’t go to closed loop. The frequency valve is working and 02 sensor is fine. It seems to have been an issue to occurred suddenly.

It’s also so bad it won’t hold idle (it idles below 500 while stumbling )

Any thoughts?

[dmcnc]

First thing is, are you using a dwell meter? Otherwise you're shooting in the dark. Second, I would inspect the injectors (including the cold start) for leaks, spray pattern and fuel volume.

[David T]

Check the plunger inside the metering unit. If it gets stuck it can make the motor run VERY rich.

[Jonty]

Thanks all - yes it’s with a specialist using a dwell meter hooked up to a proper external 02 reader. The dwell never moves from 45 no matter what the mixture is set at. I did wonder about the plunger.

[Bitsyncmaster]

Thanks all - yes it’s with a specialist using a dwell meter hooked up to a proper external 02 reader. The dwell never moves from 45 no matter what the mixture is set at. I did wonder about the plunger.

If your getting a constant 45 deg then your lambda ECU is not seeing the O2 sensor voltage going above 0.4 volts. Even with the mixture wrong you would see the minimum (about 12 deg) or maximum (about 85 deg). It may be your lambda ECU is not working or another common problem is the two grounds get disconnected. The grounds are in the harness and run to the engine block.

[Jonty]

Thanks Dave - it shows 85 with the car off. The dwell does change if I disconnect the 02 sensor. Any idea where to find the grounds? Thanks very much

[David T]

If the plunger gets stuck the muffler will glow red. If you aren't seeing that but you can't get the dwell working, you need to test the Lambda system. Refer to D:04:15 in your Workshop Manual para 5 A to E. Your O2 sensor may be contaminated. Also consult the repair notes on the preceding page.

[Jonty]

Thanks Dave - I tested it as per manual a few weeks back and it was fine so something must have gone wrong

[Jonty]

Dave - I was just thinking about this and wouldn’t something wrong with the lambda system not matter if it is too rich at idle in closed loop? Isn’t mixture in closed loop not affected by the 02 sensor?

[Bitsyncmaster]

Thanks Dave - it shows 85 with the car off. The dwell does change if I disconnect the 02 sensor. Any idea where to find the grounds? Thanks very much

With the engine off there is no power going to the lambda system. So reading dwell engine off means nothing since there is no signal coming out of the lambda ECU.

There is a wire with a ring terminal attached the passenger side engine head. That wire goes to a connector with the mate in the engine harness. Often that connection gets disconnected.

There are two ground wires for the lambda ECU. Pin 5 goes to the blue bulkhead connector (#22) and pin 16 goes to the blue bulkhead connector (#23). In the engine harness those mating blue connector wires are joined and connected to a one pin connector which then mates to the ring terminal. They use the engine block ground for the lambda to reduce noise because the O2 sensor ground is the engine block.

[Ron]

There is a wire with a ring terminal attached the passenger side engine head.

I think you meant the passenger side intake runner? If so, more detail HERE (http://dmctalk.org/showthread.php?11945-Unsure-of-dwell-reading&p=181425&viewfull=1#post181425).

[David T]

You are only in "closed loop" if you see the dwell fluctuate. Many things can prevent that but the bottom line is if the mixture is way off (and it doesn't take a whole lot for that to happen) then you are not in closed loop. A vacuum leak (or leaks), a contaminated O2 sensor, a misadjusted mixture screw, a bad, leaky/dirty fuel injector, are just a few of the things to look for. Of course bad electrical connections in the Lambda system can do it too. Do you hear the Frequency valve buzzing?

[Jonty]

I had the system going closed loop a week ago and after sitting for a few days I started it and it was only running on 4 cylinders and sounded awful. Unfortunately I messed with the mixture setting too much so I have a specialist to reset the base with a proper 02 sensor but it still doesn’t explain how randomly it went rich for no reason and fouled the plugs. We are tying to get the mixture right after cleaning up the plugs then will try get it to closed loop. Historically I’ve had quite a bit of hassle getting it to go closed loop so something is not right. Yes the FV is working.

[David T]

When it happens all of a sudden on a car that is being used at least once in a while, I would look for an electrical problem. Misfiring cylinders would show rich running because you aren't burning the fuel in those misfiring cylinders and instead dumping it out the exhaust. Bad ignition wires, bad dist cap, that kind of thing would do it. It is never a good idea to just start with the mixture screw, that usually won't fix anything and should only be touched after you have everything else working perfectly. Also it is VERY sensitive and a minor twitch is enough to alter the A/F ratio a lot.

[Jonty]

Hi all

Bit of an update. I have a specialist looking at it who remains baffled. He found initially most of the plugs were fouled hence it was runnning on 4 cylinders. He’s clean the up and got it running but it won’t accelerate. He thinks it’s now very lean and is baffled as the mixture screw does not appear to richen it up. Like me he’s baffled as to why the mixture screw is not responding as usual. He said it is responding slightly but not much. He going to go through a full fuel pressure check next when he gets back to it.

He did say it is blowing a bit of smoke (which it has never done before). Just for pease of mind how much could bad compression cause symptoms like this and could it happen quickly like it seems to have done for me? The motor only has 16k miles on it

[David T]

Since you have been fiddling with the mixture screw you need to get it back to as close as you can. There is a procedure where you turn it to where the injectors just start to spray at idle. If the mixture screw doesn't have a lot of effect either you are WAY off and/or you have a lot of vacuum leaks. Remember, you MUST plug the hole over the mixture screw once it is set or that is a huge vacuum leak! Before you can attempt to adjust dwell all of the injectors must have a proper spray pattern and open and close at near the same pressures.

[Jonty]

Thanks David. Yeah the issue is the specialist is looking at it and has a proper external 02 meter plugged in and he simply can’t get it to richen up. He doesn’t believe there is a vac leak but will run a smoke test.

You are also right about the mixture bung. On my car particularly if you remove it even when it was tuned well the vac leak was so large the engine dies instantly. Will make sure he knows that.

[Bitsyncmaster]

Pressure check is a good next step. If that checks out I would guess it's a problem with the fuel distributor. Try some injector cleaner in the gas tank to see if that helps.

[Jonty]

Thanks - funnily enough I have recently used injector cleaner and I’m starting to wonder if it dislodged some crap. David - what would poor compression show up like?

[Bitsyncmaster]

Thanks - funnily enough I have recently used injector cleaner and I’m starting to wonder if it dislodged some crap. David - what would poor compression show up like?

Poor compression would not cause you not able to adjust the mixture. It may change the mixture but the FD has a wide adjustment for mixture. Same if your lambda system was not working, you still should have mixture adjustment via the adjustment.

[Jonty]

Thanks David - really appreciate your help

[Ron]

Pressure check is a good next step.
+1

Since the dwell was off after it suddenly went south, you probably have to fix why before you can get it to stay in closed loop. Nothing is screaming electrical so I'd confirm the primary and control pressures. (Could be the PPR o-ring or a dozen other things.)
Once that is done, get a decent initial setting as Dave T mentioned. Basically, you put the easy injectors in a bucket and make the pump run continuously. Quickly turn the adjustment screw until the injectors start to spray then back it off until they just stop. Put everything back to normal and it should fire up. You may have to baby it or adjust the dwell screw so it will idle and warm up, allowing you to set the dwell. It is always the last setting and touchy so turn it in increments a small as you possibly can or it may go 'out of bounds' and make you think it is not working.

[Bitsyncmaster]

+1

(Could be the PPR o-ring or a dozen other things.)


+1

The PPR o-ring can go bad suddenly.

[Jonty]

Thanks Ron and Dave. I did reset the injectors as you describe and still no joy so defintlay control pressures next on the list. Will let you know result in case anyone else has the issue.

Cheers both

[David T]

While it can't hurt to check the pressures, if they are way off the motor wouldn't run. More important to check the injectors for opening and closing pressures and spray pattern. BTW, sticking an O2 sensor after the catalytic convertor and trying to adjust the mixture screw is not the way to do it. Either follow the procedure or remove the O2 sensor and measure BEFORE the cat. (I am assuming you measured post cat with your O2 sensor).

[Jonty]

Thanks Dave - he’s checking from behind the Cat.

[Jonty]

I did call in today and noted he was tuning the mixture without a bung in so took my old bung down that I drilled a hole in to slip over the Allen key. My car is super sensitive to the bung being out (it will die instantly if it’s out). That hopefully helps him.

[Ron]

That's odd. I have never seen one that would die because of the adjustment hole being open...usually it doesn't even take it out of closed loop. With yours running rich enough to trash the plugs, I'd think it would like it going a little bit lean...

[Jonty]

Hi Ron - that’s exactly why this thing is throughly confusing me. It’s just not behaving normally as what you suggest was what I initially assumed. Something is messing with the mixtures so that’s why I’ve sent it in for someone to reset then start working through it. When it fouled the plugs it was running in closed loop perfectly the day before!!

[Jonty]

Ron the one other symptom I haven’t mentioned was that when it was tuned and went into closed loop particularly you often heard what could be described as a “clattering” noise that would come and go. I’m starting to wonder what out of adjustment valves might be contributing?

[Ron]

Hi Ron - that’s exactly why this thing is throughly confusing me. It’s just not behaving normally as what you suggest was what I initially assumed. Something is messing with the mixtures so that’s why I’ve sent it in for someone to reset then start working through it. When it fouled the plugs it was running in closed loop perfectly the day before!!Yeah, it's hard to say if it is something getting worse (~OK but finicky in the very beginning) and/or something new or ??.
I still have to say check the 2 pressures. Everything is based off of the Primary Pressure...just too many ratios reacting with too many variables, with little being linear, including the Control Pressure...
I'm not betting on it, but the example of a bad PPR o-ring could fit: The Control Pressure counteracts the plate that the CO screw adjusts. If the Primary Pressure is off, the Control Pressure will be off anywhere other than where it was set (at idle, warm). A flattened o-ring could cause that. And if it then had a smile/chunk come off of it the pressure would be off a lot... Others: The WUR could of taken a dive, trash in one of several places, etc. Checking BOTH could eliminate a lot of potential problems while pointing to others...

[Ron]

Ron the one other symptom I haven’t mentioned was that when it was tuned and went into closed loop particularly you often heard what could be described as a “clattering” noise that would come and go. I’m starting to wonder what out of adjustment valves might be contributing?Was it doing that before you had trouble getting it into closed loop?

It would be odd for a non-pushrod engine to go from what I usually hear referred to as "clattering" to quiet (lifters running dry-lubrication). Maybe "ticking" or "pecking"? I'd have to head it. Anyway, the valves being too tight or loose will affect the burn. But it would be fairly consistent and doesn't fit all of the other symptoms well imo.
A compression check could shed some light on that, but there are other tests I would do first. :deviltail:

[Jonty]

It occurs mainly in closed loop but I think that is because it hunts slightly in closed loop and as the engines rpm goes up as it hunts you hear the definite clatter then it stops as the rpm goes down.

[Ron]

You didn't say when you first heard it?
VID?

[Jonty]

VID? I’ve heard it since I owned it (a few months).

[Ron]

Sorry, can you post a video for us?

[Jonty]

No sorry it’s in the shop.

[Ron]

Did it go away when cruising?

[Jonty]

I couldn’t hear it while driving. Was only really noticeable when in engine bay.

[Jonty]

The other odd thing Ron was that the dwell would never read above 45 unless you hit the wot switch or put a battery across the 02 lead and it went to 89. It would never as part of normal operation no matter how you adjusted the mixture sit anywhere between 45 and 100. It would often sit at 11 and when I didn’t have it turned it would swing between 44 and 34 but if you richen it it would go to 45 stay there (as opposed to swinging at say 55-45.

[Bitsyncmaster]

The other odd thing Ron was that the dwell would never read above 45 unless you hit the wot switch or put a battery across the 02 lead and it went to 89. It would never as part of normal operation no matter how you adjusted the mixture sit anywhere between 45 and 100. It would often sit at 11 and when I didn’t have it turned it would swing between 44 and 34 but if you richen it it would go to 45 stay there (as opposed to swinging at say 55-45.

I would think your lambda ECU is working since you could get the min and max values from it. But it is weird to can not adjust the mixture also so maybe the ECU does have a strange failure. I do have the ability to bench test the ECU if you want to send it to me. Or if you can borrow another owners ECU to test in your car. The ECU is a pain to remove the way it's mounted.

[Ron]

The other odd thing Ron was that the dwell would never read above 45 unless you hit the wot switch or put a battery across the 02 lead and it went to 89. It would never as part of normal operation no matter how you adjusted the mixture sit anywhere between 45 and 100. It would often sit at 11 and when I didn’t have it turned it would swing between 44 and 34 but if you richen it it would go to 45 stay there (as opposed to swinging at say 55-45.
It looks like everything is ~normal and you are turning the screw too much at a time. Basically, the ECU wants the voltage produced by the O2 sensor to be ~0.45V => 40° dwell. If the voltage is a little above that, it starts leaning it out until it gets a little below 0.45V, then it starts to enrich it. It constantly walks it back and forth across 40° dwell. I don't remember the D's exact range, but for most cars, anything below 0.10V or above 0.90V is out of range (undefined) and will cause it to go open loop, so if you turn the screw too much either way, it will go to 45 steady.

Your numbers etc. (in order):
45 steady- It's forced by the ECU or in open loop.
Normally, hitting the WOT grounds a circuit in the ECU which forces 50°-60° steady. Applying 1.5V forces 20° max steady. Grounding the 02 lead forces 87° minimum steady (so 89° is OK). It shouldn't sit anywhere else except when you disconnect the O2 sensor or it is set out of range, either will force it to 45° steady (40°-50°). When you saw 11° it was probably turned way too far (CW) rich. This would make the voltage high and, like applying 1.5V, it was forced to 11° (meets 20° max steady, so OK). Swinging 44 to 34 is good enough (35°-45° swinging, OK). From there, depending on how much you then richen it (or lean it out), it will swing if it can maintain a range near normal, otherwise it can go to open loop. (Not that cut and dry but hopefully helps...)

If I saw 44 to 34 and wanted to put it right on spec, it is so touchy that I would expect to make several attempts before turning it an amount small enough to do so. It's a matter of how smooth that particular screw turns and luck, lol.

[Bitsyncmaster]

My car is really sensitive on the adjustment. You just turn the adjustment as small as you can and it moves about 10 deg. of change. So that small adjustment change is less than 5 deg of rotation of the adjustment screw.

[Ron]

I would think your lambda ECU is working since you could get the min and max values from it. But it is weird to can not adjust the mixture also so maybe the ECU does have a strange failure. I do have the ability to bench test the ECU if you want to send it to me. Or if you can borrow another owners ECU to test in your car. The ECU is a pain to remove the way it's mounted.+1
That sounds right to me, but I would put a good 02 sensor in it, check the pressures and, if OK, try again first...

:headscratch:...:dunno:

[Jonty]

Solved!! Thanks for all your input guys. Just heard back from the specialist and he spent Sat afternoon going back and resetting the whole system. Turns out two things. One the oil filler assembly had failed resulting in a huge vac leak. Also there was a small blockage in the WUR breather so no wonder I have having issues. It’s running better than I have ever had it so stoked! It turned out it must have been going too lean (maybe the clatter/pinging noise I heard) which ended up causing a misfire and that fouled the plugs (I assumed it was too rich). I made things much worse by tampering with mixture. I’ve learned many things but one is never touch the mixture if everything else is not perfect (I think Dave preaches this all the time).

Last question for you all but my idle now is wonderful and so smooth but on my gauge it reads just below 1000. I’m assuming these gauges aren’t super accurate because when it idled at 700 ish it was horrible. The idle now sounds brilliant.

[Bitsyncmaster]

Stock idle ECU is set to hold 775 RPM. I think your RPM gauge should show close to that if the RPM is 775. You can put an external RPM gauge connected to the ignition coil.

[Ron]

Solved!! Thanks for all your input guys. Just heard back from the specialist and he spent Sat afternoon going back and resetting the whole system. Turns out two things. One the oil filler assembly had failed resulting in a huge vac leak. Also there was a small blockage in the WUR breather so no wonder I have having issues. It’s running better than I have ever had it so stoked! It turned out it must have been going too lean (maybe the clatter/pinging noise I heard) which ended up causing a misfire and that fouled the plugs (I assumed it was too rich). I made things much worse by tampering with mixture. I’ve learned many things but one is never touch the mixture if everything else is not perfect (I think Dave preaches this all the time).

Last question for you all but my idle now is wonderful and so smooth but on my gauge it reads just below 1000. I’m assuming these gauges aren’t super accurate because when it idled at 700 ish it was horrible. The idle now sounds brilliant.Cool!

If I'm following you, wild guessing- I's say you were right about it being rich (because the WUR wasn't able to adjust the control pressure properly to begin with) making it finicky. Then the new vacuum(s) leak caused the misfires, contaminating the plugs, and pre-ignition pinging. ie normaly one will start and run with the filler assembly completely missing, but the vacuum leak overwhelmed the ISM (system) and WUR/CPR (already having trouble).

+1 on checking with external RPM gauge.
Also, at idle:
Check that the Idle Speed Switch is being pressed and going to ground (Hold the throttle open a little, press the switch and listen for RPM change).
Note: Idle spec is 775 RPM +/- 50
Check the Linkage: Not too tight, etc..
Confirm that Control Pressure is 49psi - 55psi when the WUR/CPR is warm (>104°F).
Confirm that Vacuum is NOT going to the distributor.
Check for small vacuum leaks.

[Jonty]

Thanks both - it did use to idle at an indicated 775 but it stumbled and always felt like it was about to die and now it is idling at an indicated 950 it idles like my modern Honda. I really hope it’s just a gauge issue as I love the new idle!

Also it’s had a full smoke test. The oil assembly cap still needs to be to be replaced (he’s done a temp repair) so will recheck it all when the arrives from DMC

[David T]

If you heard a clattering it might be a good idea to check your valve clearances especially if you have over 30,000 miles on the car and you don't know if or when it was ever done. Reset the Lambda counter. That vent hose was the subject of ST-18-10/81 and is important for the right control pressures. That could have caused an over-rich condition even with a large vacuum leak. Also wouldn't hurt to do ST-32-12/81 and check all of the vacuum hoses. Make sure the delay valve on the CPR is oriented correctly. The Tach is not accurate enough to adjust the motor to. Your idle should be 775 + - 50 RPM. One of the best indicators of how well the car is in tune is to check your gas mileage. Once you get the motor running right you should change the oil (and oil filter) if you were running very rich. Some of that gas got into the oil and diluted it.

[Jonty]

Great thanks Dave - the engine only has 16k miles. I have done all vac hoses other than the 3 under the manifold

[Jonty]

Also the idle seems to have settled to an indicated 750 so it’s all perfect (touch wood). It’s amazing how much havoc a vac leak can have! Thanks again to Ron and Dave for all the help.