Andrzej
Member
- Joined
- Oct 29, 2005
- Messages
- 42
- Location
- Amersham, Bucks
- Car
- 1997 W140 S600, 1980 Porsche 928 4.7 Manual
I'm normally pretty adept at sorting out mechnical/electric problems, but this time I'm stumped. I've also learnt over the years not just replace electronic parts until I can prove that they are dead first (especially when very expensive!).
Anyway, here is the history:
I go to start the car... the engine turned over put didn't start which it's never done before. So first off I repeat again listening for the fuel pump which came on ok. All the dash lights looked correct (this is the M104 engine but a 1989 model with no diagnostic light in the dash). Next I checked sparking by removing one of the plugs. Nothing. So then I move straight to the coil. No output here either. Next I remove the coil altogether and check it over. All looked fine and the resistances of the primary and secondary coils all checked out fine. I gave it a quick clean before refitting.
Next I did some research. I've got schematics, read lots of forums etc etc. I found that as this car has got a 9pin diagnostic connector I can connect pin 3 via an LED and 10K resistor to ground, then by grounding this pin 3 for 3-4 seconds a diagnostic flashing code will be visible. This sounded like it would reveal the problem. Looking at my schematics pin 3 does go straight to the ECU. Anyway, when I try it, I just get a constant dim glow from the LED, ie. no diagnostic output at all. Is this in itself enough to be confident that the ECU needs replacing?
I've also been advised to check the OVP (over voltage protection) relay with the fuse on top - this seems to be fine, certainly the fuse is ok. I tried reseating too.
Does anyone have any other ideas at all?
Anyway, here is the history:
I go to start the car... the engine turned over put didn't start which it's never done before. So first off I repeat again listening for the fuel pump which came on ok. All the dash lights looked correct (this is the M104 engine but a 1989 model with no diagnostic light in the dash). Next I checked sparking by removing one of the plugs. Nothing. So then I move straight to the coil. No output here either. Next I remove the coil altogether and check it over. All looked fine and the resistances of the primary and secondary coils all checked out fine. I gave it a quick clean before refitting.
Next I did some research. I've got schematics, read lots of forums etc etc. I found that as this car has got a 9pin diagnostic connector I can connect pin 3 via an LED and 10K resistor to ground, then by grounding this pin 3 for 3-4 seconds a diagnostic flashing code will be visible. This sounded like it would reveal the problem. Looking at my schematics pin 3 does go straight to the ECU. Anyway, when I try it, I just get a constant dim glow from the LED, ie. no diagnostic output at all. Is this in itself enough to be confident that the ECU needs replacing?
I've also been advised to check the OVP (over voltage protection) relay with the fuse on top - this seems to be fine, certainly the fuse is ok. I tried reseating too.
Does anyone have any other ideas at all?