Stalling problem after harness swap - Third Generation F-Body Message Boards

Maverick H1L · 09-22-2009, 07:08 PM

First off, to those who helped with the 730 harness swap,

. Second, I AM running VATS in-line with my aftermarket security system, which is set to disable the ignition power to the VATS module in the event of a system trigger (disabling the VATS system instead of the starter because I didn't want an enable AND a disable relay on the starter's yellow wire from the ignition switch). I have NO problems starting the engine. The first time I did the swap, about 2 months ago, before I had the VATS module and I was running an FWD MEMCAL just to run, I was on my way home from the parts store and ended up disabled in the middle of a major intersection. I originally thought the problem to be the ignition module, so I replaced it. About a week later, the second module (or whatever the problem is) did the same thing as I was backing out of the driveway. I ended up going back with my 302 system up until last week, when I had bought the VATS module and was waiting on a couple of other things to get done before inspection time. After I installed the VATS along with the 730 harness (and replaced the ECM because the one I had gotten from the donor with the harness had been exposed to water and I was thinking it was shorted inside), the car ran great up until yesterday, with the only problem being my brake light being on. I got out of work yesterday, started the car, and left the parking lot to come home. About 1/2 mile down the road, the car stalled again. I turned the key off and let it sit for a minute, and then it started again. Another 1/2 mile and it did it again. It did this twice more until I got home. At first, I thought the problem had something to do with being under load, but when I let the car run in my driveway after getting home, it stalled again in a minute.

Symptoms include: Severe miss about 2 seconds before it shuts off. Will not fire after stalling without sitting with the key off for a minute. Also, even weirder, when the car stalls, the ECM intermittently jumps into the diagnostic mode (turning the rad fan on and turning the SES light off to send codes), but only for a short instant, and does this repeatedly until the key is turned off. Fuel injectors continue to fire until the engine completely stalls... this is how I believe this to be a problem somewhere in the ignition system.

I KNOW the ignition and fuel parts are good because they work with the 302 system just fine. 2 ignition modules and 2 730 ECMs do the same thing. I have checked the connections at the coil and the module, and all are good with no loose or broken wires. I'll go through tomorrow (provided the crappy WNY weather holds out) and do a resistance test on the wires between the ign module and the ECM. This IS an intermittent problem, so it seems... The engine ran for about 15 minutes in my driveway this morning with no problems (except a mild misfire which I will take care of once I deal with this bigger issue).

I'm looking for any suggestions here, and maybe some help from someone with a 90-92 FSM (preferably the No Start flow chart and the EST diagnosis). Also, I am looking for some ground distribution wiring diagrams as I have all the rest that are relevant to my system from Austin ThirdGen, but they don't have the ground distribution diagrams. I know of a ring terminal in my harness that has 2 light blue wires attached to it that is near the heater box that I don't currently have hooked up (IIRC I think it's for the SIR system, but I couldn't swear to it). I'd REALLY like to be able to get to the junkyard so I can grab the EGR valve assembly and the wiper motor from the donor car and another ECM bracket, but I can't currently trust the system to make it the distance.