curtisr

I've been working on converting an '87 924s to a track car for some time now and yesterday I finally got to take it to the track for a shakedown cruise. Naturally I suspected that I would detect problems but I didn't think I would create a new one. And a new one I did. I forgot to bolt the battery down....

All seemed to be going rather well until the last tight corner when the engine quit and I could see smoke coming out from under the hood by the window. I pulled off the course, jumped out--glad that the fire extinguisher was installed--opened the hood and found my battery was sideways and the battery cable insulation going to the cutoff switch was smoking! Yikes! Clearly the positive post was in contact with the hood. Thankfully there was no fire and I was able to correct things and head back to the pits.

After repairs were carried out I was ready to head back to the lapping. The engine revved fine (without load) and was able to stay running through out the rpm range. But that wasn't to prove to be the case for long. Now, however, the car was having trouble holding the rpms; the engine seemed to be 'bogging down'. After a couple of laps it got worse, I couldn't find the sweetspot on the gas and limped back to the pits with a top speed of about 25 kph. I shut the car off and re-started it to see if it would still chug or work normally (the definition of futility danced upon my mind). It still chugged. Shut it off, let it sit a few minutes and then tried it again. It was normal. So I trailered it and went home.

Did I cook the ECU? Something else? As always, I thank everyone who stops to read this and respond, in advance.

Roger 'Cooked' Curtis

931guru

Probably cooked the ECU due to voltage surges.

Arominus

Try another battery and check the output of the alternator, dunno if you would have seen higher voltages out of the battery in a short condition like that, the short is a huge load on the system that i could see nuking the alternator and hurting the battery.

V2Rocket

yea, i'd try another battery before suspecting the ECU.

GPA951s

BTW you mentioned the hood it contacted with. It seems that black thing back by the windshield is where it would hit. I just Cut mine out on the track-car, that way if the battery slides it cant contact anything.. Would have nice if the Original Design made the neg post where it "Might hit the chassis"

jderimig

Another thought.....

With the battery shorted the system voltage could have gone very low which would which might have caused "chatter" on you fuel pump relay which could damage the contacts on the relay leading to intermittent fuel pressure.

WolfeMacleod

I did exactly that same thing with my first 924, a 1977, way back around 1991. It burned up one wire from the fuse box, all the way to... I forget...maybe an ECU? up near the driver's side headlight.
Wound up having to rewire the entire car with what amounted to zero automotive experience.

curtisr

This was/is my biggest fear...

Did it today. The output was 14.25 volts at the battery. Alternator seems to be fine.

Curiously, the battery still works. Last time I did something like this the battery blew up. Luckily no one was injured.

Agreed. Can't count how many times the +'ve terminal has hit that piece.

I decided to start with the easy stuff first and I'm pleased to report that after replacing the DME/Fuel Pump relay all appears to be well. Mind you it was a short test drive and even less time revving the motor in the driveway!

Thanks for your help everyone. I hope this case can be considered closed.

curtisr

Yikes! And this was the second time in my life I had to grab a burning/smoking electrical wire(s) (the first time was with a coil wire) and yank it out.

ECU Doctors

Before you damn the ECU use this chart to check all the inputs and outputs of the control unit.

http://site.ecudoctors.com/tech-data...w-up-Forms.pdf

Hopefully you can find a bad wire or something easy to fix.

Let me know.

curtisr

That is one amazing diagnostic table! I'll be printing that off... thanks!