car dies what to look for?

[mb911]

ok my car is prety far from stock in the fuel and igntion catagories it has the following to give you and idea

MS ECU for the EFI
12 plug dizzy customer curved for my application
msd 6al
msd twin coils

and most the orginal harness is gone from the cis etc.

When driving the car it runs well but yesterday while cruising the car @3000rpm the car just died. I looked to make sure all the power was still on and it was. as soon as I hit the key to restart it fired right up..

I tend to think it was just the stock fuel pump relay but how often do they really go bad? I am thinking ECU issues but am hoping not.. any thoughts

[dean]

I would guess a wiring problem. Most ECUs are very reliable. All it takes if one bad connection and your car dies. I would try to eliminate things. Can you hook up a laptop while driving to see if the ECU looses power? You could make up a test light for fuel pump power and see if the light goes out when you car dies.

Good luck

[DDDD]

You always have to at least consider the voltage regulator making power spikes happen...

[copbait73]

Don't forget about ALL the ground wires. Many more in these EFI systems.

[equality72521]

Mine was doing that and it turned out to be the red over boost relay in the back. Replaced it and problem is long gone. Relays do go bad.

[mb911]

it did it to me once last year right before I put it away. I figured it was a fluke. So I rewired to clean up everything back there and got really good grounds. etc. I am hoping upon all hope that it is just the fuel pump relay but could be voltage spikes as well..

[copbait73]

I swapped a 3.2L from a roll over into a '71. Had start and run issues then finally found a corroded/intermittent ground in the engine harness. Lots of them with Motronic.

[mb911]

I read some of the guys run filters on the main power to the MS or any ECU for that matter to prevent V spikes. Maybe worth a shot

[h20cooled7]

possible ignition switch

[copbait73]

Ben, is your motor still Motronic with crank speed and position sensors?

[mb911]

Originally Posted by h20cooled7

possible ignition switch

thats new



as to what eninge it is an 81sc engine base with 3.2 intake and 98mm 8-1 turbo pistons(je) running MS as the fueling ECU running an 12 plug dizzy for ignition.. I fire two coils with 1 MSD.. I just drove it again and did it once for me. it started right back up as soon as I cranked it

[martinb930]

Fuel pump relay BINGO... my car was doing the same thing and once replaced, problem solved.

[930gt-40r]

Im wondering if the MSD is having a fiesta at your expense...
Ive had intermittent problems with my old 6al before.

[RarlyL8]

Don't discount the ignition switch. They commonly go bad with age as the connections simply wear out. Sometimes just wiggling the key with the car running will reveal the issue.

[mb911]

Originally Posted by 930gt-40r

Im wondering if the MSD is having a fiesta at your expense...
Ive had intermittent problems with my old 6al before.

I have often suspected it but kind of a somewhat expensive trial and error thing

[mb911]

Originally Posted by RarlyL8

Don't discount the ignition switch. They commonly go bad with age as the connections simply wear out. Sometimes just wiggling the key with the car running will reveal the issue.

replaced it last year with a new one..



oh and put a different relay in for the fuel pump with no luck

[911boost]

As your set up is pretty custom, do you have an overboost switch built in. I know this topic has been brought up a lot, but the overboost will cut the fuel pumps, and if you have a short in there somewhere it may be bad enough for the car to stall.

[mb911]

Originally Posted by BSiple

As your set up is pretty custom, do you have an overboost switch built in. I know this topic has been brought up a lot, but the overboost will cut the fuel pumps, and if you have a short in there somewhere it may be bad enough for the car to stall.

No it does not. But It seems very ignition related as it is very pronounced when it dies like key switch vs fuel would be a little bit slower I would think

[raceman]

well you need`d a fuel pressure gauge anyhow l agree that it sounds electrial in nature. lf my car was doing that l`d be paying attention to Exactly when it happens:warm? cold? bumps? etc. Get out the multimeter and start checking from the battery outwards,you`re checking resistance values and continuity. lf you installed the systems in your car l`m sure you`ll find the problem.The first thing a Porsche tech would say is"check the relay under the drivers seat" ,on the 3.2`s that was the most common failure that fits your cars` symptoms..

PS_pics of the car?

[mb911]

Originally Posted by raceman

well you need`d a fuel pressure gauge anyhow l agree that it sounds electrial in nature. lf my car was doing that l`d be paying attention to Exactly when it happens:warm? cold? bumps? etc. Get out the multimeter and start checking from the battery outwards,you`re checking resistance values and continuity. lf you installed the systems in your car l`m sure you`ll find the problem.The first thing a Porsche tech would say is"check the relay under the drivers seat" ,on the 3.2`s that was the most common failure that fits your cars` symptoms..

PS_pics of the car?

yeah no relays on my car as it was an sc based engine.. it happens anytime mostly after a while of run time.. kind of crazy