Very strange electrical/fuel issues.

[railgun]

This is about as odd an issue as I can imagine.

Quick history here...I recently had a short develop between the ECU and the FJO driver box for the front primary channel. Long story short, the ECU fried because of it. I replaced it with another Power FC. Everything to that point had been working flawlessly. I ran most of last year with the same setup. The cause of the short was due to a rewire of the harness. I did not replace the FJO unit, but I did relocate it to the pass side footwell to remove it from the heat it was given (it was on the fender wall on the pass side).

Fast forward to now. This issue has ocurred three times within the last three weeks. The first time, the problem started after about 2-3 min of driving and cured after about 10. The second was yesterday afternoon on a cold start and was cured after about the same amount of time. The third was early evening after about 10 min of driving and was cured after about 15 min.

After the first time, the car was fine for the rest of the night, which was another six hours of on again, off again driving in the area totalling about 100 miles. Last night was about 30-40 miles worth of driving with no repeats.

The issue is that the car just up and dies, whether under power or not. Initial troubleshooting shows that I have spark and at least fuel pressure when the condition is present. I haven't been able to see whether any injector is firing, but I'd presume not since if it were, I'd expect the car to fire. It does crank with no issues. Occasional restart attempts are met with a quick fire for all of a second or two, then dies again. It's not trying to run on one rotor, it's nothing at all. Just smoothly turns over with no attempt to kick at all.

Other than disconnecting and reconnecting some things (FJO box really) and moving some wires around, which doesn't seem to do anything anyway, there's no logical reason why it dies in the first place, let alone what causes the condition to resolve.

So I have several questions here, other than the obvious, which would be to replace/check the FJO box. I'll get to that in a second...

The EGI relay: When removed, does that cut ignition, fuel, or both? I know that maintains the pumps so... The theory there is that it's starting to get in bad shape. After many remove, replace sessions using not the best tool (pliers) it's started to crack a little. Perhaps it's flaking out on me.

The security system: When active, does that cut the starter or one or both of the above? No reason to suspect this so much, but I'm curious just the same.

The FJO box: There's no logic whatsoever to why it would randomly die like that. I'm going to check whether the gound I'm using is good enough. I would seem to think so as I've wound it out several times and it seems fine. Unless I hook up an ammeter to the thing and see if it stops drawing anything, I don't know how else to check the thing.

Wiring: I'm not a professional wire guru by any means, but I will toot my own horn and say that the harness is done very well. I made sure of that after the last hack job I apparently did...which is another thread.

Sorry for the long thread, but I felt it necessary to be as descriptive as I can and not be another "My car doesn't start. Why?" and that's it thread.

Thanks in advance.

[joff]

Originally Posted by railgun

The FJO box: There's no logic whatsoever to why it would randomly die like that. I'm going to check whether the gound I'm using is good enough. I would seem to think so as I've wound it out several times and it seems fine. Unless I hook up an ammeter to the thing and see if it stops drawing anything, I don't know how else to check the thing.

You can get a pair of Mechanic's Stethoscope for like $5 at Harbor Freight and put it on the injector to listen for the injector pulses. Since you have spark, it seems almost it has to be the FJO or the injectors. Don't know how your ECU fried, but its conceivable it failed in a mode that turned on the injectors to 100% duty cycle and if that happened without fuel pressure it might be prone to overheat the injector coil windings.