howyadoin

Just thought I'd throw this question out there in case anyone has any suggestions. I have a 91 5.0 out of a GT in a rock crawler...this is my third "rock buggy" with a Mustang motor and they've all been amazing. Anyway, I was doing some fab work on the body and tripped the "impact sensor". Obviously, this seems to have tripped something that shut off the fuel pump and it wouldn't start.
After tracking that down and resetting the switch, it still won't start. I have great fuel pressure at the pump and the fuel rail. I also have spark at the distributor...so I'm REALLY confused. I'm definitely not a mechanic, but I certainly "know my way around" vehicles. My question is, how is it possible that I have spark, I have fuel pressure, and it's definitely "sucking air"...but it doesn't even attempt to fire??? It crank perfectly, just doesn't even act like it's trying to think about starting?
Anyway, if anyone has any ideas, I'd definitely appreciate ANY input!

mattdel

Did you "trip" the inertia switch via heavy contact with the car, or did your fab work involve welding?

dawson1112

IF you were welding on it I hope you disconnected the battery ground..

howyadoin

No welding...tripped it because I was banging around in the area...I definitely tripped the switch and definitely fixed that issue...fuel pump works fine now. The injectors themselves obviously aren't working...I'm just troubleshooting power everywhere to try to isolate it...just didn't know if the tripped inertia could potentially cause any other issues in the ecm or anywhere else?

mattdel

Nope, the inertia switch is basically a relay between the pump and the pump relay. It's incapable of causing damage as wired from Ford. However, depending on how you wired your buggy, a short in the system(depending on year of computer/harness) could cause a short to ground at the computer. You have a 1991 harness, which means this applies to you. Pre-90 wouldn't. The wire leading from the FP relay to the inertia switch also ties into a computer PIN, of which # I can't recall at the moment.

As far as the injectors go, their timing is coordinated by the PIP, inside the distributor. It's not linked in any way to the inertia switch. No injector pulse has 3 main culprits(aside from wiring flaws): PIP, TFI, Computer.

howyadoin

Great info, really appreciate the input. I'm going to work on it again tomorrow...hopefully it's something simple that I missed in my first quick "lookaround".