My 93z has had some inconsistent starting/dying issues and I’m not sure where to get started. Previous to two weeks ago the car has been running great then I took it to class with no issues, left class with no issues, stopped to eat lunch and the car would start but would idle 200-400 and fall flat on its face if stepping on the throttle. Turning the key to the on position and I couldn’t hear the fuel pump at all (normally it’s very obvious). Towed the car home and let it sit for 3 days, tried it again and it fired right up no issues and ran like it normally did.

Last weekend I took it to class again, drove there fine with no issues. Left class and it started fine again, got about a mile down the road and everything just shut off at about 50mph. SES light quickly came on but went off. I coaster to the side of the road and waited for a tow. The car will turn key on but there is zero cranking, can’t hear the fuel pump again, I have dash lights but that’s about it. Is this likely a bad ECM? Shoddy ground somewhere? Kinda at a loss as to where to even start trying to figure something out. Thanks for any help.

 

I would start by checking fuel pressure

 

Have you determined if it is a bad fuel pump?! It still does not explain what you describe as the car not even cranking. I don't want to scare you with this comment since I had A LOT of crap happen to me when I had my remanufactured Jasper engine put in by a shop that certainly should be removed from the Jasper recommended shops list.

I had shorty headers put on since the engine would already be out but the wires were never protected, they were exposed to the heat of the headers and melted and ended up shorting out my PCM one day. The car started, ran funny, and once I shut her off and came back to start her up, no cranking, no dash lights, NOTHING! If you have power to your dash then I can't say your PCM died, that is also rare unless you did what I did with the shorty header swap. When a few of my optisparks died, the car would crank yet not start at ALL. I do remember an instance where the car would not crank and I had battery power! After having replaced an optispark last year the car would run but suddenly die! It was not the fuel pump but clogged fuel injectors!

Also, a bad EGR valve stuck in the open position will cause bad idle problems which can lead to total stall out if the diaphragm is shot. It was also a lovely discovery I made last year diagnosing my car.

 

So when you say "zero cranking" you're saying the starter does not engage? If that's the case along with the fuel pump not getting electricity (because you can't hear it prime) then it sounds like an electrical issue. Something related to the starter and fuel pump only. The intermittent nature could be due to a loose connection somewhere. You should scan that SES to help narrow things down further.

 

I had the same issue recently. The positive battery cable looked good, but when I removed the boot and 2" of sheathing discovered the cable was shot. Replaced, not a problem since. Car would start normal, then next time nothing, no starter, no fuel pump buzz, just dash lights. I even swapped 2 batteries thinking that was the issue.

 

Just because you can hear the fuel pump doesn't mean it's producing enough pressure. You need to find out what code the PCM is throwing.

 

Thanks all, some really good suggestions here. I haven’t had a ton of time to work on the car as I’ve got a 71 Camaro eating up all my garage time. However, I ended up checking the fuses again and the 15amp ECM fuse was blown. Easy fix, just replaced it. It immediately blew the replacement fuse the second I hit key on. Most likely have to find a short now. I’ve been taking body panels on and off because I’m in the process of repainting the car but can’t imagine I caused the short working on the bumpers? I have a Haynes manual for the car but I’m curious how many circuits are tied to the ECM fuse? Hopefully I’m not trying to locate it over a ton of circuits. Thanks all.

 

I’ve still been trying to trace this thing. The car hasn’t started for a few weeks now. I’ve been looking at wires and connections and everything looks good. I tried to pull codes off it but the ECM fuse blows immediately when I key on. I’m really clueless what might be causing the ECM short. Does anyone have any thoughts?

 

1) Hook up fuel pressure gauge.
2) Key on engine off (with PCM fuse out)
3) Jump this connector http://shbox.com/1/fuel_pump_prime.jpg
4) Listen for fuel pump and watch pressure gauge
5) if pressure is weak (<40psi) at KOEO or pump does not run start checking electrical stuff here:

 

Thanks for the input. I’m out of town this weekend but will give this a shot when I get home.

 

So I disconnected various connections, coil, icm, Ecm, etc and turned the key on to try and trace where the short was. The fuse still blew every time. I wiggled the fuel pump harness at the connection and tried again. Fuse didn’t blow this time. I was able to jump the DLC to pull codes. Only code that came up was 12. Dash light were really dim so I put a charger on the battery and tried to crank it. ECM fuse blew again and the car of course wouldn’t crank. Is it possible the battery was low enough after I wiggles the pump harness that it didn’t have enough amperage to blow the fuse? Or should I continue to focus my attention at that harness? I ran out of 15 amp fuses so will get some more today and try to jump the fuel pump with the priming wire tonight. I’ve been looking at the schematics and it’s difficult to tell, but is the fuel pump part of the ECM fuse circuit?

 

I believe I found the culprit in case anyone stumbles on this thread with a similar issue. I traced the short back to the fuel pump harness. Once I got the sending unit out I saw the connector to the sending unit bulk head had the gray wire melted to the ground. Luckily the Racetronix kit has a new connector for the bulkhead.