RennBod

I made a massive mistake. I offered to help a friend at work to get his 964 C2 cab working, thinking it would be as easy to cure as everything I have needed to do to my 964 turbo. But alas no!

Its a 1992 C2 tiptronic Cab, that was running fine until recently.

He noticed the indicator for the tiptronic gear selection wasnt working, even though the car was driving ok, he checked the fuses. Found a blown fuse (he does not remember which fuse it was) and then all his trouble started.

At first it broke down about 3 times, where it just cut out and would not re-start... Now it will start for a split second and then stall.

We hooked up another friends AutolandD91 Porsche fault code reader and it raised a hall sensor fault... So we cleared it, tried to restart the engine and it came back.

So with my experience of lurking in here, I thought "A-HA!.. Check the caps, rotors and leads"... the leads were fine, but the distributor caps and rotor arms were in a very poor state...

Once changed... Still no start... and still a hall effect sensor error after an attempted start... Disconnect the hall effect and it acts exactly the same.

Now for the really odd bit!

The other day, we managed to get it idling, rough but idling by disconnecting the tiptronic ECU. But plug it in and it will not start again.... Tried this again today and it will not start with the tip ecu plugged in or not.

We also tried a DME and Tiptronic ECU from another friends car... Still no start.

Another thing we have tried is disconnecting the ignition amps one at a time to see if it makes any difference.... It didnt

We even went to the extent of changing the flywheel sensor for a new one... It was very old... its not expensive.. it kept us out of trouble for an hour or so.

Another odd thing... With the other 964 C2 Tip and another friends 993, the AutolandD91 will work if the ignition is on, or if the engine is running... On this 964, when it was running for that short time with the tip ecu unplugged, the AutolandD91 was acting REALLY odd... Resetting, corrupted screen all kinds of odd stuff.. Almost as if some voltage spikes, grounding issue or either too many volts or not enough volts are going through the diagnostic port.

Last odd thing.... When trying to start it, the cab hood warning light flashes, the DME relay clicks randomly (seems to be in time the the engine firing and not firing)... I tried bypassing the DME relay with a jumper wire, still no start... Tried another DME relay... Still no start

Tomorow I think we will check the distributor drive belt has not skipped a tooth and I think I will take the alternator belt off just in case its over charging (even though it only shows 13.5 volts at the battery when it was running for that short while!)

So. H E L P ! ! ! ! ! ! !

david@st ives

Renbob

Try reading this post , you may get a few pointers

https://rennlist.com/forums/964-forum/303640-flywheel-sensor.html

A good place to start is to see if you are getting a signal at the white wires at the ignition modules.

I had similar starting issues before my car finally died

Good luck and do keep us informed

Dave

RennBod

Thanks Dave,

By the looks of your thread we are both currently at the same position. But I have tried a spare DME which runs fine in another car and it still does not run on this one.

I am begining to think its either the wiring to the DME relay, or the alarm system.

I really want to know how to bypass the alarm unit (the alarm unit under the seat in an aluminium box) I believe it also acts as a primitive immobiliser and I suspect that internally it may have a fault... but unless I can bypass it, I can not rule it out.

Anyone able to give me some clues about the alarm module/controller (928 part number)... Ideally I could do with knowing if it does immobilise any circuits in the car and if it does, what pins I need to jumper to bypass any form of immobilisation.

HELP!

RennBod

Tonight I have been doing some more research, and it would seem that part numbers 928.618.260.00 (01, 02 and 03) are for the 964, early 993, late 928 (92 to 95) and the very last 944 S2.

Looking on those rennlist forums for those models I have managed to find out that one of the pins from this module feeds power to the DME, acting as a form of immobiliser (not feeding the DME with power when the alarm is set) which on these other models gives exactly the same problems as we are suffering from...

So does anyone know which pin on this alarm control module feeds that power to the DME, so I can check its being output by the module, or if its faulty (without buying a new module!) Also... what pin does the module get the 12v signal to feed the DME with?

JasonAndreas

Pin #4 on connector #1

Term 15.
Pin #6 on connector #1
Pin #18 on connector #2

Richard Curtis

Coincidentally, I just happened to download Adrian's update/corrections to his book (page 388 specifically) and have them lying here beside the keyboard. The correct page 388 has a "Motronic troubleshooting" chart that lists several reasons why a car won't start.
-- Alarm immobilizer system active
-- no fuel
-- ignition system failiure (faulty coils common)
-- fuel pump failed
-- flywheel speed refrence sensor failed
-- idle speed control valve failed
-- throttle valve stuck closed
-- resonance valve stuck open
-- DME control unit failed

for Tips only:
-- transmission position switch incorrectly adjusted
-- transmission position switch failed
-- If Tip trans switch is incorrectly adjusted or has failed it can be cross-checked by checking reverse lights. If reverse is selected (lights serviceable) and lights do not come on, this confirms a transmission position switch problem.

You didn't say in your first post whether you observed a spark at the spark plug. If you did see a spark, the spark color has to be blue. If any other color, you have a bad coil.

You also didn't report if a spark plug was "wet" after cranking. If not, you're not getting fuel to the plug, and hence have a spark-delivery problem.

RennBod

Thanks Richard,

The plugs are wet and the spark is intermittant and weak.

Is it common for both coils to go down at the same time?

or do you think its possible that one has been dead for a long time and its only when the second one dies that the problem is noticed?

Anyone have any idea why the plugs would be wet (indicating that the DME is working and firing the injectors) but the ignition system would be down AND the DME relay clicking in and out randomly?

AndrewM

Had a similiar problem on my 89 C4, code kept reading Hall sensor, it was the coils.
Drew
89 C4 (sold)
98 C4S
86 930

Richard Curtis

Rennbod: you need to check two plugs... one each for each coil... to see if spark is same for both.

You might also try cleaning the main ground from the negative battery cable to the body. Clean both ends of the cable and the body connection. I wouldn't be too concerned about the DME relay clicking until you've gotten a good, strong, blue spark. Let us know how you fare.

JasonAndreas

If you can hear the DME relay clicking doesn't that usually mean there is a supply voltage problem?

Peter Badore

Have you tried your alarm control module in another 964? Or vice versa a known good alarm module in your 964? There is a relay inside the alarm control module that routes circuit 15 battery plus voltage from the ignition switch in on alarm module pin 1-6 and out to the DME relay on alarm module pin 1-4. For airbag equipped 964s the circuit 15 plus voltage is further routed through the airbag module before going to the DME pin 86. Also, the coils are 964 are suspect although the 964 coils are common with the 944, the heat generated in the 964 location causes them to fail which in my guess is much more often than in the 944 chassis.
I do not have much experience with tiprontic Porsches but I wonder if the tiptronic ECU could be grounding out the circuit 15 feed to the ignition coil control units? Did your 964 blow fuse no. 27?
The DME's first relay contact points send battery + out on pin 87 to a lot of places including the tiptronic control module pin no 1. If the tipronic module is malfunctioning, then I suppose it could weaken the available voltage to the ignition system. Also, did you measure actual fuel pressure at the test port when cranking the engine? As Adrian's book and supplement point out there are lots of no start fault conditions. Please don't ask me how long it took me to sort out my 90 and 92 964 s no start conditions. It took a long long time.

RennBod

Update.

Disconnected the ignition modules, cleaned the contacts.. Ran a spark test, and it has a clean blue bright spark.

Reconnected the coil leads to the caps and she fired up!

So I do not know if she is going to start again later... or if indeed she is fixed or what the cause was...

Keep your fingers crossed!