JCF

When the engine dies, I still have ignition.
I tryed swapping the coil with a new one, and I said in my first post, tested the fuel pressure in the ramp (with a BOSCH gauge, accurate).
When the engine stops, it stops almost as a ignition cut (not long stall then die...) ; but when checking, still have ignition and injection...
The DME relay "knock" after the engine stops, so the system is still powered.
Mad thing.

theiceman

you gad pressure when it ran ... how about when it didn't ?

JCF

No problem when the car doesn't run : the pressure go down (about 2.2 bar) when cranking and firing (because of the vacuum) and when the engine dies et stops, hold 2,5 bar.
And the pressure grows quickly just after I connect the gauge (even when my problem occurs) so the pump does its job...

JCF

Today, I let the Motronic opened (very carefully) to try to find a overheating component. I started the car and let it warm. After several time, never cut. I try to "shake" the DME relay and I can sometimes have a engine stop, but it's not the same problem because I can hear and feel the switch by the coil in the relay (moreover, I tried to shunt the relay and when the problem occured, it didn't change anything). Remove the cap on the relay plug to see if wires could be bad soldered or cut, nothing. I will all the same buy a new relay.
Today, I think I let the car running (at idle with some throttle moves) during between 30 and 60 minutes, and it never fail. 10-15 minutes makes it cutting before. Very very strange behaviour which doesn't help me to solve this problem...

rusnak

+1 on Iceman's post #17. I'd keep the gauges on there, as well as a spark tester. When it stops, (not while it is running), before turning off the key, did you check to see if you have 12v input power to the ignition coil (terminal #15)? It is powered from the key, not the DME module. If not, then you may have a bad ignition switch. I just re-read some notes that I took, and no power to terminal #15 was thought to be due to a bad ground in a previous thread this year on Rennlist.

JCF

I think I have some difficulties with English and I apologize about that. This test was done and all was fine.

It's a very interesting thing and I will check this as soon as possible (or as soon the problem comes back). On my wiring diagram, the 12v at the coil is provided at the fuse box and powers also the DME relay (which is still powered during the problem), so I thought that if the DME was powered, except cut wire, the coil should be powered.
But.... after 86 the diagram changes as an anti-theft powers the relay. In my case, there's not anti-theft... but maybe was it removed. Moreover, I had spark during the problem, but you're absolutely right that I've to check this.
Hope I can do it tomorrow and will let you know...
Thanks for giving me your time.

JCF

No problem today, tested again a long time... The engine never stopped. I did nothing that change the configuration. Will try a road test tomorrow if possible.

JCF

I understand nothing. Today was a good weather day so I can test the car ; and as yesterday and 2 days ago, it runs perfectly. I don't understand. One week ago, the engines systematically died after 10/15 minutes and after, the starting was erratic. Before and today, there was no problem. Not once. And I don't really know why, I just made some solder at the DME relay connector but I don't think they could lead to this kind of problem (and the old ones were not bad).
Hope never have this problem anymore. In all case, I've new sensors, which is not a bad thing knowing how look the old ones, and I've fix a possible ignition problem because of the cold solder in the DME... To be continued... maybe.

Jascha-M

I am a little late to offer much for the 'Suggestion Box'... the symptoms you described at the start of this posting are characteristic of a bad head temperature sensor that has a 'high' resistance value (k-ohm) when cold but quickly changes to 'low' resistance (ohms) when engine warms up... The miraculous recovery is not not consistant with this common problem.

Hope it lasts...!

JCF

No problem with the "little late", any proposition is well appreciated ! But unfortunately, I controlled the head sensor and it never give me a short / open or a bad value. Controled both in the engine compartment and at the pins of the Motronic. Moreover, when the problem occurs, disconnecting the temperature sensor makes the engine runnning... instead of dying (dying which occurs when disconnecting the sensor when the engine works fine). That's why I think about an over-lean mixture, countered by the over-rich mixture of the open-circuit at the sensor when removing. And as I said, no problem since a few days...

88CarreraTarga

Hey all. I need some confirmation regarding the reference sensor. If there is spark at the "test" spark plug, then that means the reference sensor is working, correct? Otherwise there would be no spark at all if the reference sensor is not putting out a reference pulse, right?

I have a 1988 911 3.2 that started after still being warm, ran for a few minutes, then just died and will not start. I too went through all of the tests listed above in this post, yet no joy.

I’m running out of ideas.

88CarreraTarga

Update to my earlier 10/15/2011 post...

After going through all tests described in the “Carrera 3.2 no-start” thread, I finally fixed the issue I was having with the engine stopping, and then not starting again regardless of engine speed or temperature. The issue was intermittent.

In summary, the fuel injector analog circuitry board associated with the 12 volt to ground power transistors in the DME had some oxidation/corrosion as well as intermittent cold solder points.

Here is what I did to find the issue. After performing all of the other system checks, I removed the DME and disconnected the connector from the DME, then reconnected. I then turned the key and the car started. So I was pretty sure the issue was either with the connector or the DME. The connector ended up checking out OK, so that left the DME.

I then found and downloaded the DME circuit schematics (87-88 3.2), as I suspected my issue had something to do with fuel injection circuitry (based on all of the other tests). After opening up the DME (which I had done before to put in a performance chip) I was not seeing anything visibly wrong inside. However, what I had NOT done before is to take the bottom metal plate of the DME off. Once I did, I found oxidation/corrosion as well as what looked like cold solder points on the bottom of the circuit board associated with the analog power transistors for the fuel injection circuitry.
After using Isopropyl Alcohol to first clean the circuit board area, I used a magnifying glass to confirm my find of the cold/broken solder joints, and then used a small soldering iron and fresh solder to re-solder the suspected circuit points as well as touch up some other areas that I thought might be “suspect” of cold solder.

After reassembling and installing the DME, as well as many hours and miles of operation afterwards, no more problems. The car runs (and continues to run) great.