'79 930 won't idle "dieseling" and stalls running rich

[wnmimms]

Hello,

Hoping someone can help me out. Car was initially running but turbo wasn't boosting. I tracked that issue down to the gaskets in the recirculating system body, they had become brittle and were holding the piston open and allowing the charge to be diverted back to the turbo rather than through the throttle body. I fixed that but now the car won't idle, it seems to be very rich when I do seem to get it to start but will "diesel" and then stall. I have read through the "my car won't start" sticky on the Pelican forum which has a pretty daunting list of possible issues. I have also included a link to a sound clip and uploaded it to YouTube. (Link below).

https://youtube.com/shorts/W9cEqV8W_uA?feature=share

Any suggestions on where to start? Or should I just start working through the list of possible issues on the Pelican Forum?

[Alan L]

It is probably a fuel issue. The first place I would start is with the WUR pressures. CIS gauge needed.
Checking Cold pressure and Warm pressure are in spec. That sets your mixture.
Alan

[wnmimms]

Thank you Alan. I just placed the order for the CIS pressure gauge... should be here April 14-17. If I could get it running long enough I'd try checking for vacuum leaks.

[Alan L]

It could be a bunch of things. I had seals (O rings) fail in the FD and had symptoms like that.
Another thing you could do is run it for 5-10 sec then shut it down. Now put your hand on each header - which ones are hot? Is it running on 6, or only some? That is how I found my faulty FD. One side of the engine had hot headers, the other side was cold. Took a while to figure that one out.
Alan

[DSM]

How did it run before recirc system was repaired? Example: It started, idled & ran good or normal other than not building boost?

[wnmimms]

Initially, it was idling and was fine through the rpm range but with no boost. I reached out to the forum and was advised that the piston might be sticking in the open position allowing the charged air to be sent back to the turbo. After removal of the recirculating system and disassembly of the piston/valve I noticed that the piston was in fact stuck open due to the crumbling seals.

I was eager to confirm that that was in fact the problem so I used some form-a-gasket to seal up the piston bore at each end. The car was now building boost, and seemed to be running fine for a bit. I drove it about 15 min and then it quit on me and I couldn't get it started again, but after sitting overnight it started right up and I got it home.

Thinking I may have a vacuum leak at the form-a-gasket repair I sprayed a bit of carb cleaner at each end of the piston and noticed that when spraying the cleaner it pulled some of it in and brought the idle down which seemed counter to what I was thinking... Either way it wasn't a tight seal so I disassembled everything and just waited on the gaskets to arrive from Pelican.

I installed the gaskets in the recirculating housing reconnected everything making sure all the vacuum lines were tight and went to start it and it won't idle and when I am able to get it to run it sounds like the sound clip I initially included.

I have ordered a CIS Pressure testing kit which should arrive a week from today. I was able to get it to idle for about 5 seconds... not enough to build up any meaningful heat to see if all cylinders were igniting. I will let it sit a bit and see if I can get it started again to test with my IR gun.

Thnaks for the help! Bill

[Alan L]

5 Secs would be enough to see if all headers are even for heat. Probably are, but if not, that sets us down another track.
Sounds like something in the intake system, but checking the fuel (WUR) pressures is always a good baseline start to poor running.
Alan

[patina]

Without a wideband it's hard to say if you're running too rich or too lean. If you feel you are running too rich, give the mixture adjustment screw at the fuel head a 1/4 turn counter-clockwise. It's a 3mm allen head that is inside a plunger. The plunger must be in the "down" position to be adjusted and it is a very fine adjustment.

You can always remember:
"R" = Right Turn (Clockwise) = Richen.
"L" = Left Turn (Counter-Clockwise) = Lean.

[wnmimms]

Alan, when I had it running for about 5 seconds I was getting a temp reading of about 70F from cylinder to cylinder. It's in the lower 60's today so I am assuming that they are all equally firing.

Patina, I can certainly make changes to lean it out to see if that helps.

I am totally assuming that I'm running rich just based on the strong smell of exhaust, but you do make a good point on the Wideband O2 sensor.

Quick question though.

What would necessitate an adjustment to the AF mixture if nothing has changed. I will say that the car is completely original. The engine has never had any major work done, we have had the car since the early 80's...the car was purchased new in '79 and kept in Germany for 5 years so we could import it free from emission regulations (grey market). Just 45k on the odometer.

[Mike80911]

You touched on a vacuum leak. I had that issue once and turned out to be a pretty significant vacuum leak. Try to go over everything very carefully and make sure there is not a leak somewhere

[Alan L]

Yes there are some awkward hoses on that recirc valve system. Silly Q but are they all where they are supposed to be.
Nice looking car.
Alan

[wnmimms]

Alan, I believe so... there are certainly a bunch of them. I'm pretty confident that they are all where they are supposed to be given they are almost "preformed" given their age... it's almost as though they can only go to one place. I presume they could have cracks in them under the fabric wrap that I can't see. I'll check through them tomorrow in hopes that I can find where I may have some leaks.

I may just take an inventory of the various sizes and lengths and order a set of replacements to cut to length.

Thank you for the compliment on the car. I just love it. So fun to drive but I don't need to tell you that. I am also really enjoying learning more deeply about the various systems. Off hand do you know of a good reference that details how each system works? The fueling, electrical, vacuum, etc.... I have the workshop manuals but they don't offer a lot in the way of how it all functions. Thanks! Bill

[Alan L]

I don't know of any 930 general explainer.
But there are various generic CIS manuals - which explain the heart of the beast.
If you can't find any references to one I will post something in a day or so - I have 3. They are extremely useful - cover everything from WUR function/design to CSV systems, Accumulator designs and function, fuel pumps etc.
Regards
Alan

[DSM]

More than likely a vacuum leak. Stick with what you know. It ran good before repair. Do not adjust CIS or anything else until you get it back to how it was running before repair. If you make adjustments now you will likely introduce more variables making it harder to diagnose/correct later or possibly compensating without correcting actual problem.

Video clip note: Other than idle stumbling that baby sounds healthy. I love color coded fuchs. She's a beauty!

What would a car run like with a vacuum leak? Common symptoms are rough idle and hesitation, accompanied by unusual vibration, and often a hissing noise. Vacuum leak allows unmetered air into the engine, which will cause the engine RPM to rise and then fall. Individual cylinders go rich and lean and experience uneven power strokes. This is much more noticeable at idle because of the larger time gap between power strokes and because the leak has a greater influence on the air/fuel ratio than when the engine is under load. A significant vacuum leak may cause the engine to stall.

[Bucketlist]

It sounds like you may have a vacuum leak. When you introduce air into the system thru a vacuum leak it will throw off most of your adjustments resulting in a poor AF ratio and a car that may not run well. I agree with Alan that measuring CCP and WCP are the first step. You can put your battery on a charger and turn on the ignition to run the fuel pumps and warm up the WUR and measure the WCP without the engine running. You may have to pull the green plug at the rear of the air flow meter to make the pumps run. If you still have running problems once you get these pressures within spec try to run a smoke test by injecting smoke into the system thru a vacuum port. You will see signs of smoke from the air flow meter or air cleaner unless you cap it off but by then you should see smoke from a problem area which will be obvious. There are many ways to run this test including the purchase of a smoke generating device or the old school way...blowing smoke from a long drag on a cigar. Once you have completed these tasks and the repairs needed, a wide band air fuel gauge is a necessary addition to keep an eye on things.
Good luck!

[wnmimms]

Alan, thanks for the suggestion, I’ll do some digging in generalized CIS manuals.

DSM and Bucketlist, I’m with you. If it was running fine with the exception being lack of charged air through the throttle body and then started acting up after the replacement of the gaskets and disturbing all the vacuum lines the least complicated culprit is a leak in a line somewhere. I’ll continue to move forward with obtaining a baseline on the CIS when the testing equipment arrives and have ordered a smoke machine that arrives tomorrow… really appreciate your help and will keep you posted. Stay tuned. Bill

[Alan L]

OK - just had the chance to listen to Vid link. It does sound like an airleak (biggish one). Sounds like a very lean miss.
Something not right in reassembly of intake system. My guess. One way to confirm would be to richen the idle mix (clockwise). Temporary to see if get expected response. More fuel at idle should compensate for the extra air and idle should progressively improve. This adjustment is very sensitive. A half turn usually takes you from one extreme to the other. So take note of the position of the allen key once engaged in the adjuster with the adjuster depressed and locked in place (you will feel the resistance when you go to tweek the allen key). Take note of the o'clock position, then turn clockwise - hopefully while idling. If it won't idle at the start, turn it 1/4 turn and try again. That should be enough to tell you if you are heading in the right direction. If you can get an improved idle then I suggest tearing down to the recirc valve again and check everything. Put the idle mix screw back to where you started from.
Another thing to try if it will idle, is pinch the AAV hose. While cold this unit is bypassing extra air past the TB butterfly, to assist the richer cold fuel mixture produce a higher idle. Cutting this flow off should improve the idle if it is an airleak.
May also be a pinched O Ring - IC or recirc valve body.
Alan

[Alan L]

Can't remeber where I sourced it - prob Amazon.

[wnmimms]

Alan,

I received the smoke machine today.

Interestingly, the last time I was able to get it to fire was during the video that I uploaded. Now it seems at though it's not getting any fuel at all. It doesn't smell rich and am unable to smell gas at all.

I removed the charged air recirculating system again and completely disassembled it, checking my work and the gaskets that I had replaced, everything seemed fine. I reconnected all vacuum hoses and carefully checked for tightness at each connection.

I connected the smoke machine to various points in the system. I was only able to get smoke from two places the large opening into the charged air recirculating system and the hose that connects tot the AAR. I plugged up both with rags which allowed the smoke to build up in the now closed system...nothing... no smoke from anywhere. I also checked the vacuum advance after disconnecting it from the distributor... no smoke....

I am wondering if I may have a clogged fuel filter, or some other fueling problem. I will follow your lead on adjusting the AFR at idle tomorrow and report back. I will be anxious to see what information the CIS fuel pressure testing kit is able to tell me after I receive it on Friday.

Side note... Thank you for passing along the Bosch CIS manual you included, I'll check Amazon. I was able to find a CIS primer that Jim did from "Jims Garage" the primer was initially included on Rennlist but now "lives" here.

https://jimsbasementworkshop.com

A lot of good information on the CIS, the various components, what they do and how they all function together. Just thought I'd pass it along if you hadn't seen it before.

I'll let you know what I find out tomorrow after I tweak the AFR.

Thanks,

Bill

[Alan L]

"I was only able to get smoke from two places the large opening into the charged air recirculating system and the hose that connects tot the AAR."
There should be no leaks - you need to fix these.
Alan