87 911 3.2 engine cut out

[vinceparts]

Hi guys,

1987 3.2 g50 german car, LHD. 100,000kms

Problem symptoms- (random)
-engine power (not instruments) completely dies out
-clutch in while still rolling, the engine starts to idle hunt with lots of unburnt fuel out exhaust 300rpm - 1800rpm
-let it idle for 10sec to a minute (never consistant) and it comes back to its normal self
-if you try rev it while its idling it dies instantly
-once it dies from trying to rev itl take anywhere from 3secs to fire up to 1minute with unburnt fuel coming from exhaust.

things ive done to TRY remedy problem
-new fuel filter
-new spark plugs
-new airfilter
-new dizzy cap and rotor
-cleaned contacts on coil
-pulled every plug in engine bay and cleaned with contact cleaner
-pulled dme relay and ecu/dme and cleaned contacts


Do you guys have any solutions. Please only reply if you have experienced or dealt with very similar or identical symptoms.

Thanks in advance. Cheers, Vince

[Bob Prosser]

Hey Vince.

See the red arrow in the photo. That device in the center of the intake should be gently vibrating when the ignition is hot and fuel pump is running. If you don't feel anything, then I suggest you give it a gentile "love tap" with something to see if you can free it up AND if then the engine will start.



Also, your flywheel sensor may need replacing. Do some research on that.

Hope that helps.
Bob

[ganun]

I always keep a spare good known DME relay in the glove, and have encountered 2 new that failed within weeks, get a quality spare.

[vinceparts]

Originally Posted by ganun

I always keep a spare good known DME relay in the glove, and have encountered 2 new that failed within weeks, get a quality spare.

I understand that. But from my research it doesn't seem like that will be the cause from the symptoms ive had.

[DRACO A5OG]

Does it hunt at a stop. If it does, next time she hunts, leave her on, open the lid and with a screwdriver tap on the ICV pictured above in red, If it clears up, remove and clean then check the OHMs on it per Bentley manual.

But what concerns me is that she stalls, which tells me she has a massive vacuum leak.

Try the Cigar Smoke Test ( any cigarette for that matter ).

AT a FLAPS, find a vacuum hose the same ID and about 2 feet long ( sorry convert to metric ) as one of the thinner hoses, connect tester hose, blow smoke into the hose and check for smoke. Crude but effective.

Jim

[cabmandone]

Originally Posted by DRACO A5OG

Does it hunt at a stop. If it does, next time she hunts, leave her on, open the lid and with a screwdriver tap on the ICV pictured above in red, If it clears up, remove and clean then check the OHMs on it per Bentley manual.

But what concerns me is that she stalls, which tells me she has a massive vacuum leak.

Try the Cigar Smoke Test ( any cigarette for that matter ).

AT a FLAPS, find a vacuum hose the same ID and about 2 feet long ( sorry convert to metric ) as one of the thinner hoses, connect tester hose, blow smoke into the hose and check for smoke. Crude but effective.

Jim

Could pull oil cap off and see if idle changes at all too couldn't he? If I recall, when you pull the oil fill cap off and the idle stays the same you have a vacuum leak. It won't tell you where the leak is but it will tell you if you have a leak or not.

No power seems strange but someone mentioned the reference sensor and possibly speed sensor as potential culprits above. I don't think you'd have a intermittent failure of those but I suppose anything is possible.

Dumping fuel would point to a CHT sensor to me. It will idle really rough and finally die if you try to throttle up. I believe you can jumper the CHT to bypass it and see if it is causing the fuel loading.

[DRACO A5OG]

Yes, you can stick a paper clip in the CHTS connector and it will bypass it. Check the OHMs ( cold and hot ) there and both ref and speed sensor for extra measure.

+1, pull the oil cap then move to smoke test to find the leak, if any.

+1, haven't read about intermittent failure of the ref/speed sensors

[ischmitz]

The fact that your issue is intermittent in my mind points to something electrical rather than a vacuum leak. In addition you say you get raw fuel. This indicates the DME is still seeing signals from the speed and reference sensor causing it to be in "run" condition. FYI, both the reference sensor and the speed sensor do fail intermittently the symptoms are different. It usually shows as cutout at certain RPM ranges and temperatures.

In your case something causes the mixture to go very rich. Two possibilities come to mind:

- The CHT is intermittently open and makes the DME think you'll have a stone-cold engine. The DME is then richening the mixture to the point where it is beyond being ignited. The result is raw unburned fuel.

- The engine is loosing spark intermittently (causing raw unburned fuel).

As others said check and verify the CHT is the later 2-wire version that doesn't rely on GND from its housing screwed into the head. If not replace it.

Next, you can measure its resistance with the engine cold (~ 2kOhm) and at operating temperature (~90 Ohm) and confirm its within spec. See the WSM for details. Keep in mind the issue being intermittent makes it hard to catch it in the act.

And then you could short it with a wire clip making the DME think the engine is fully warmed up and no enrichment is required. If that remedies the issue it strongly suggests CHT. However, with the CHT shorted cold starts will be extremely hard.

Next, the intermittently missing spark can be caused by a faulty DME. This requires inspection and potential repair of the DME.

Regards,
Ingo

[DRACO A5OG]

To take the DME out of the picture, place it in a donor 3.2, DO NOT PUT donor DME into your car. IF you car is faulty, it may damage it.

Keep us posted.

[ben parrish]

I had a very similar issue with my 86...it would do exactly the same thing and when it finally started back the unburnt fuel would smoke out the exhaust like crazy. I checked the DME and re-soldered a few suspect joints and thought is was solved but the issue reappeared. I then pulled the relay for the DME and re-flowed the joints in it..problem went away and hasn't been back. Don't rule out the relay...give it a try and see what happens.

[cabmandone]

Originally Posted by ben parrish

I had a very similar issue with my 86...it would do exactly the same thing and when it finally started back the unburnt fuel would smoke out the exhaust like crazy. I checked the DME and re-soldered a few suspect joints and thought is was solved but the issue reappeared. I then pulled the relay for the DME and re-flowed the joints in it..problem went away and hasn't been back. Don't rule out the relay...give it a try and see what happens.

Wouldn't a faulty DME relay cut fuel rather than dumping it?

[ben parrish]

86 Carrera Problems

As I understand, there are two stages...I believe that the DME cannot get power to fire but the relay can get feedback to run the fuel pump while cranking. Not an expert and only passing along my experience and what worked for me.

[ischmitz]

Originally Posted by ben parrish

86 Carrera Problems

As I understand, there are two stages...I believe that the DME cannot get power to fire but the relay can get feedback to run the fuel pump while cranking. Not an expert and only passing along my experience and what worked for me.

Correct. There are two stages: 1st stage powers DME and second stage (which can only turn on if 1st stage is on) powers the fuel pump. 2nd stage is turned on either when cranking or when flywheel pulses are detected.

However, I don't see how a faulty DME relay can cause unburned fuel so its very unlikely that replacing it will cure his original problem. Remember, a running fuel pump will not dump fuel, it merely pressurizes the fuel rails. You still need pulses to the injectors.

I have my money on the CHT or the DME itself. I wonder when we will hear back from the OP with more data.

Ingo

[69-912-swt]

I had a interment problem with my 3.2 last summer. It would cut out a few seconds at a time usually at over 3k rpm's usually after temps came up !!I found the connector for the cylinder head temp sender on the left side of the motor was all desegregated !! A temp fix was to RTV sealant the wires inside of the connector. Still working 8 months later, just got back from a 1,200 mile trip with lots of mts roads. I used 2nd a lot 2.5 to red line for many miles of twisty turns !!

[Tippy]

I vote cylinder head temp. Engine is running pig rich.

If DME related, we all bow out an let Ingo take over.