I want YOU to solve this problem ;) 911 3.2 '85 just doesn't want to start anymore

[matomorizo]

Hey guys,

I really need your help to get my '85 911 3.2 running again. It is a US model which I brought back to Germany 5 years ago.

So, far it ran perfectly. No Problem, never. but then this winter came.

After winter it wouldn't start anymore. Battery is fine, it crankes, but just won't start.

The crazy thing is that it ran about a day after using some starter spray. Then it stood for a day and again wouldn't start anymore, also not with the spray.

So, the work began:

This is what we have lready checked thanks to this fabulous forum (checklist) as well as Bentleys Manual.

- all sensors regarding ignition and fuel injection,, ignition System (coil, rotator, distributor, cap, etc), fuel supply, fuel pump, DME, spark plugs exchanged, injectors cleaned, and all sensors described to check in Bentleys
- fuel injection and ingnition working properly (fuel and spark is fine)
- opened the ECM, Looks fine

Now, we realized something:

There seems to be something about the air flow sensor, MAF:

- When the MAF is detached, the car starts, however runs poorly, so we deinstalled the MAF and opened it.

No Problem to see, except only one thing is strange: The Potentiometer has a slight interruption (it jumps from 0,5 kOhm to 0,8 kOhm and then it continues not regularly (0,7 ... 0,9 ... 1,0 ... 0,8 ... kOhm), as it should be (according to Bentley)). Is that really a sign for a faulty MAF?

So, we think that either the MAF is the Problem (if that Ohm values are the Problem) or the ECM does something wrong with the values it gets from the MAF.

What do you think? Could the MAF be the Problem? Any idea how to be sure about it?

I never read about a failure of MAF or Problems with it so far. Also, I could not Imagine how it broke from Standing.

- Is there another way to check the ECM/MAF except exchanging it? Do we miss or oversee something here? maybe a vacuum leakage? So, far nothing found.

Again, the strange thing is that it ran after giving it some help. I made a 1h ride, stopped, started again, everything fine. Then, 2 days later after Standing - Nothing.... it crankes, and crankes but doesn't want to start.


I did not find a solution to that Problem yet in the forum, but if you find something, let me know, please.

Thank you in advance for your help! A Garage would be the ultima Ratio... as it should be.


Best wishes from rainy Germany,

Mato

[DRACO A5OG]

Welcome to the Board Mato.

When you wrote MAF, I think you mean AFM ( Air Flow Meter ) because you mentioned the potentiometer.

That should not relate to your no start issue. Just maybe be a hick up on acceleration.

I did not see you mention the Speed and Reference Sensors, Did you check these? Most likely your no start issue if she cranks.

Now when you wrote battery good, what voltage did you see prior to start attempt?

Jim

If there are other 3.2 owners in your area that will help out. Ask if they will allow you to put your AFM or DME (ECU not the relay) into their car. Do not put theirs into your car as it may damage their components if your car is defective.

[matomorizo]

Hello Jim,

Thank you for your response! Yes, the volume air flow sensors (AFM) ... sorry!

Both sensors showed the right resistance values according to Bentleys. Could they be faulty anyways?

Battery is quite new and was fully reloaded ...

Thanks,
Mato

[DRACO A5OG]

No problemo!

To verify we need to put your DME into another 3.2 car, if it starts then those sensors are bad or maybe not set right.

Great, please post the voltage reading prior to start attempt.

Since you are following Bentley procedure, what is the voltage numbers at the starter prior to start attempt?

Also, what color is your spark at the connector plug ( following bentley procedure )

[matomorizo]

DME or ECM? I bought a new DME and replaced it.

So far I did not think of the starter system as the engine turns properly...

Battery voltage is 13,3 V.

[DRACO A5OG]

The DME and ECM are the same



or

did you buy this?



Check the starter's voltage prior to attempt.

13.3Volts? wow that is pretty high.

[matomorizo]

I replaced the relay and inspected the engine control module.

ok, I will check the starter voltage (tomorrow).

Why do you think about the starter? What could be the Problem?

Thanks!

[DRACO A5OG]

Check the connections especially the ground to chassis. It may look good but a good cleaning and polishing will insure a solid continuity.

When you try to start her, can you smell unburnt fuel?

What brand of DME relay did you buy?

[gearheadgreg]

Originally Posted by matomorizo

The crazy thing is that it ran about a day after using some starter spray. Then it stood for a day and again wouldn't start anymore, also not with the spray.

I'm stuck on this. Are you saying after you used the spray, and got the car started and running on it's own, you tried the starter spray a day later, and it wouldn't start *at all* with the spray?? Or simply wouldn't run on it's own after you stopped spraying?

That would, of course indicate ignition problems if it wouldn't fire on the spray.

If not, have you checked the fuel pressure before/while cranking?

[matomorizo]

@DRACO:
- I bought an original KAE.
- It smells like unburned fuel, yes.
- Will check voltage today
- We checked ground connections already

@geraheadgreg
- It did not even start again (with starter spray)
- We checked ignition at the spark plug which Looks fine
- We will check fuel pressure today, just got the gauge

I'll be back with hopefully good News...

Could the sensors or the coil be faulty despite correct resistances?

[gearheadgreg]

If it doesn't even fire on starter fluid, there is an ignition problem. That stuff burns if you look at it cross-eyed, so even a super weak spark will light it off.

Not saying that's the *only* problem, as it sounds like there might be 2 or more, but I think there is a possible and likely intermittent ignition issue. Can you check spark while wiggling and tapping wires, etc? Carefully, of course....

[DRACO A5OG]

Smell of Fuel? GOOD than we can narrow it down to ignition. +1 if starter fluid does not ignite then it is most likely an ignition issue.

Yes, the sensors could be faulty. That's why I am suggesting to test your DME in another 3.2.

Also check the CHTS, probably not an issue but I would check that too.

[matomorizo]

Thanks for your answers... just figured out another strange Thing:

With the AFM disconnected, the car starts and runs (not perfectly as the Mixture is very rich, but running steadily, seems like a Default program).

We checked the spart before, it was orange (and not blue as suggested), but do you think this would explain this bahavior?

So, I wonder if it still could be an ignition isssue. But i will check as you suggested. Could be that the spark is strong enough to ingite with more fuel, but not with less.

Thanks

[Steve W]

Check your head temp sensor. It's the gang of three electrical connectors on the upper left of your engine, the white connector. When cold it should be around 2500-3500 ohms, when hot around 200-300 ohms. When it's bad usually it causes the car to run too rich and makes the car hard to start. But likely since you smell raw fuel when trying to start it, the problem is with the DME unit (ECU) and needs to be repaired/rebuilt. This is very common now that these cars are over 30 years old and exceeding 100k miles. The DME spurts fuel into the motor when cranking, but the spark is not there, so it does not fire. If you keep cranking like for over 7 seconds and you'll flood the spark plugs and it makes it even harder to fire the motor even if you had a working spark.

[gearheadgreg]

Originally Posted by matomorizo

With the AFM disconnected, the car starts and runs (not perfectly as the Mixture is very rich, but running steadily, seems like a Default program).

We checked the spart before, it was orange (and not blue as suggested), but do you think this would explain this bahavior?

I don't know the 3.2 system well enough to say, but if the DME is bad, or if the crank sensor or some other timing component needed to fire the spark correctly, or at the correct time is sending no signal or an incorrect one, unplugging another sensor might make it go to a default program that allows it to run, but I think it's a band-aid coverup, rather than the root cause.

I had a VW Rabbit Truck back in the day, with a Passat 2.0 16V engine running Bosch CIS Motronic, which just added a lot of sensors to the simple and robust CIS system to help emissions. It would routinely puke a sensor once in a while, and I learned what other sensors I could unplug to make it run enough to get home. Silly, but when these systems get old....

[T77911S]

if you are getting spark the crank sensors are good. if it can run the sensors are good.
yes I am contradicting what I just said but make sure you have 12v on the coil.


I don't know a lot of specifics on the THIS system but on most if you remove the AFM it does have a default mixture setting, to the rich.

check the wire from the CHT to the DME. make sure it is not open or shorted.
what I would try is to actually measure the CHT resistance FROM the DME connector and compare with the CHT.

look for a big air leak.

check the throttle position switch. closed/open. don't remember what it is at idle

[matomorizo]

Did some more checks.

- We exchanged both reference and Speed sensor, pin on the flywheel is fine
- CHT values are fine
- all wires from the sensors to DME are fine
- found a small air leak in a hose, fixed, but no changes
- voltage at coil is fine
- fuel pressure is fine

Again:
With the AFM plug unplugged the cars runs! Very rich, but it runs. However, as you replug it, it dies. So I wonder really if the AFM could be wrong. However, we checked it with a potentiometer and it Looks fine.

One last Thing is the CHT sensor itself.

An expeierienced Porsche meechanic told me that the ECU usually not fail, so are the coils. Also, we did all the checks on the ECU and the values are fine.

Any more ideas?

[pmax]

Originally Posted by matomorizo

An expeierienced Porsche meechanic told me that the ECU usually not fail, so are the coils. Also, we did all the checks on the ECU and the values are fine.

Any more ideas?

Post #2.

Swap your ECU into another car and see if it works.

[Tippy]

Wouldn't the AFM being disconnected result in no fuel to run? So, it's just the priming injection that is allowing engine to start?

[matomorizo]

We tried another (working) AFM, again, unfortunately nothing changed.

That leaves us with the ECU. Now looking for another car to swap it...

Thanks for your help so far...

@tippy: But it is running steadily with the AFM disconnected. Or what do you mean by primary injection?