930 start and run mixture difficulties

[worry9]

Guys,

I need some advice please. 87' 930. I have read many of the forums on this...brilliant work on the whole.

My 930 has a relatively fresh slightly tweaked engine ie K27 turbo and 964 cams, BB exhaust otherwise standard. Was running perfectly, then suddenly leaned out and had starting problem...ie low idle speed, misfire, backfire "popping".

Hooked up fuel pressure and found cold start WUR pressure too high at 2.8 bar. Adjusted brass pin to attain 1.8 bar cold. Warm at 3.7 Bar. System pressure over 6 Bar. This all looks good. Engine starts, but still lean...back firing and running rough.

Put in New plugs, new rotor button, new cap. Timing good.

Sprayed ether around all joints seeking vacuum leak. No reaction. fuel pressures all good.

Adjusted mixture screw and idle screw to it ran smooth again. Had to turn more than I expected, which raised concern. But engine seemed happy, started well and all good, hot and cold. Problem solved, but it worried me why and how this had occurred in the first place.

Went for a drive all, good. Full operating temp, all good. Stopped for 30 mins, came out to start, then engine suddenly ran hugely rich. Black smoke and low rough idle speed etc. Brought it home, returned mixture screw back to somewhere around its regular spot and engine returned to running well. Have driven it for a week or so with no bad habits, then suddenly its back to very lean again. ie back firing, low idle etc. Again sprayed ether etc no apparent leaks. Nothing has been touched in recent week. Shut the ARR line off and no reaction, so no air from there. WUR pressures and system pressures good, 12V to both WUR and ARR.

Can some one offer advice? Whilst the WUR provides control pressure to the fuel head, what happens at the fuel head? Is it possible that the fuel head is not responding to control pressure? Something sticking in mixture control? Help, doing my head in.....thanks guys.

[kevin930t]

Just wanted to say thats excacly the situation yhat i am in.I have been chacing this same prob for well over a month.I have gone through the frnt snd back.Hope someone here can help..kevin

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[356911930]

You may have a fuel pump gong out. Do either of the pumps make much noise?

Rahl

[kevin930t]

My front one but its more of a buzzz

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[mark houghton]

Could simply be one of the fuel pump relays is not working, or working intermittently. Usually when they stop working, they're dead forever. But perhaps your started working again after you monkeyed with your mixture settings.
The next time you have the original symptoms, go up front and pull each relay, one at a time, so see if you can find the culprit. At the very least you'll confirm or eliminate the possibility.

[RarlyL8]

Is your Lambda system intact or has it been disabled?
The symptoms you describe are consistent with failing Lambda system.
You didn't say how the engine performs on boost, if it boosts properly there is no issue with the fuel pumps or relays. Reduced fuel pressure/volume will cause rich idle/cruise and very lean boost, to the point of failure to boost.

[kevin930t]

The problem i am having now is when i start the car cold it runs good idles fine for about 30 seconds then goes pig rich and starts to dtumble on itself,so i shut her down with the key to off positionn and it cotinues to run on buttt (some of ronnies favorite subjects) then it goes back to running proper..

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[kevin930t]

Originally Posted by mark houghton

Could simply be one of the fuel pump relays is not working, or working intermittently. Usually when they stop working, they're dead forever. But perhaps your started working again after you monkeyed with your mixture settings.
The next time you have the original symptoms, go up front and pull each relay, one at a time, so see if you can find the culprit. At the very least you'll confirm or eliminate the possibility.

Thanks mark great idea,will definitely do that.

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[kevin930t]

Originally Posted by RarlyL8

Is your Lambda system intact or has it been disabled?
The symptoms you describe are consistent with failing Lambda system.
You didn't say how the engine performs on boost, if it boosts properly there is no issue with the fuel pumps or relays. Reduced fuel pressure/volume will cause rich idle/cruise and very lean boost, to the point of failure to boost.

I have not wanted to put a load on the motor since its running so crappy.So i dontvreally no how she runs on boost.I am really puzzled like i was saying runs good for 30 seconds then goes to hell shut her down with the key then goes back to running good until finally shuts down...any help is more than appreciated..

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[RarlyL8]

Does it only run badly upon cold start (when warm can you turn it off and start right back up)?

[worry9]

Thank you for the advice and Happy New Year all. Writing from Australia, hence delay in reply.

Seems to run fine on boost, although don't want to try that too often. Its no boost where it is really cranky.

Starts OK, I say, just ok, in that once off the initial start injection, I can sense misfire backfires, then starts to stumble moreso as temp comes up.

Lambda system disconnected and has never been connected in the last 5 years I have had her.

Runs worst when at full temp. Have tried starting, shutting down and restarting.

In desperation, I cranked the mixture screw round to rich and tweaked idle and it ran well at all rpm for a day, until something "changed" where she ran ridiculously rich, so I returned mixture to original spot, and ran well again for a week. It has then "changed" again and ran crazy lean. Most odd.

Appreciating your support gents. Cheers Cam

[RarlyL8]

Could be that your WUR electronics are failing. To go any further you need data from AFR or fuel pressure, real time. Is there anyone close to you that would allow you to borrow a known good WUR for testing purpose? Before doing that it would be good to verify all the connections are tight and not corroded such as the main plug in the wiring harness and the small plug to the WUR. Check all your related fuses and relays as well for good connection and no corrosion.

[worry9]

It could be. It was a reco unit some years back...but of course they are old electronics.

Question though, if WUR electronics are iffy, why then do I get correct control pressures of 1.8 Bar cold rising gradually to the full 3.7 bar at warm or with in say 1-2 minutes of plugging in the electrics?

If I saw incorrect control pressures I would have the culprit immediately I would expect?

Obviously control pressures must control the fuel ratio in the fuel head. The higher the control pressure, the leaner the mixture. I wonder how the control pressure actually adjusts the mixture? Could there be something "sticking" in the actual mixture adjuster in the fuel distributor , because it certainly seems to "work or not work" even though WUR fuel pressures appear timely and in spec.

Thanks again!

[kevin930t]

Originally Posted by RarlyL8

Does it only run badly upon cold start (when warm can you turn it off and start right back up)?

She starts up after 30 or so seconds as thats as long as i have been letting her run,after that its a very dramatic change in behaviour.Smokes ,coffs then lopes,then i shut the key off and she goes back to a perfect idle..H op e u have a awsome newyear to all..

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[kevin930t]

Originally Posted by worry9

It could be. It was a reco unit some years back...but of course they are old electronics.

Question though, if WUR electronics are iffy, why then do I get correct control pressures of 1.8 Bar cold rising gradually to the full 3.7 bar at warm or with in say 1-2 minutes of plugging in the electrics?

If I saw incorrect control pressures I would have the culprit immediately I would expect?

Obviously control pressures must control the fuel ratio in the fuel head. The higher the control pressure, the leaner the mixture. I wonder how the control pressure actually adjusts the mixture? Could there be something "sticking" in the actual mixture adjuster in the fuel distributor , because it certainly seems to "work or not work" even though WUR fuel pressures appear timely and in spec.

Thanks again!

Sounds like we have a similar problem,i hope u get it solved.I have been dealing with mine for quite a while ..Happy new year dwn under

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[RarlyL8]

Bonne Anne!

This is where having Control Pressure readings and AFR readings real time comes in handy. If AFR variation follows Control Pressure variation the problem points to the WUR, if control pressure and AFR are at odds the problem points to the FD.

[Alan L]

it sounds like Worry9 has acess to WUR gauges?. In which case, as Brian suggests, maybe do a fuel system check when it misbehaves again and see if readings still in spec. Depending on what WUR fuel system gauge you may have, you may be able to leave them hooked in for a short while and see if they change when it goes all wobbly. That will confirm or eliminate the WUR/and fuel pumps/relays.
Alan

[T77911S]

something changed and you should NOT have corrected it with the mixture screw.

I would set the mixture for warm running since that is how it is normally set and fix the cold issue since that seems to be where the problem started.

I would start with the WUR. perhaps its time for a rebuild.
also check the inlet screen for dirt. that can raise the CP, but would also raise WCP.

I would then look for air leaks. there is a lot of plumbing in the intake system that can leak. check the up pipe from the turbo to IC,. also the big ORings

[worry9]

Gents, I owe an apology. There is a Lambda system.

Engine appears to be still running consistently lean, hot or cold. I only adjusted mixture to get it just to start and run, and have since turned it back to almost where it was originally.It runs rough and pops. If I set it to where it has been for 5 years plus, it would not run at all.

Just to repeat again:

I have pressure gauges and WUR and system pressure all tracks correctly 1.8B ar Cold, 3.7 hot and 6+ Bar system. Engine stumbles and pops hot, cold anywhere. Only way to get it to run smoothly is the richen the mixture. I know this is only masking the problem.

I will get an AFR meter to check. however,I am sure it is running lean right through. On boost, runs fine for the brief moment I test it.


Thanks again for everyone's interest.

Cannot find any vacuum leaks by ether spray around all points.

[RarlyL8]

The symptoms described are typical for failing Lambda system. Fortunately you can unplug it and set the AFR to 13.0-13.5:1 at idle (3.0% CO) and be done with it.