This car is close to having an encounter with the 12 guage.



First off, I have an 85 z28 with the 305 tpi. It hasn't had a single problem in the past 3 years since i put the whole thing together, until now. While driving down the road it stalled out, no sputtering... just instant death. This was after blowing away a couple honda's earlier that day.. but that's a daily thing and the car is used to it. I coasted it to a parking lot, checked everything, turned the key and it started right back up. Didn't have a problem until 2 days later when it happened again. This time it took about 5 minutes before it started up again. I tore into everything and started checking. Replaced the fuel filter (it was due anyway) and checked all the usual suspects, everything was fine. I took the ignition module in and had it checked. They ran it 5 times and it checked out good. I bought a new one. just in case. It didn't solve the problem, the very next day it died again. I checked fuel pressure, no problems there. Now that the problem has gotten to the point where the car is dead I find that the injector pulse is intermittent. I let the car sit and just idle in the driveway, it died after about half an hour. Went out, turned the key, it started right back up and idled for 3 hours before I had to call it a night. Now it will only start for a second when cold (from the cold start injector) then die. I put a noid light on it, it blinked once and that was it.

Heres where I am so far:

--pickup coil ohmed out at 850... ok
--replaced the module even though the old one tested good...
--have spark
--have fuel pressure
--checked ground strap
--checked the fuses
--oil pressure guage and tach both register when cranking, so i'm assuming those sensors are good
--tried starting with the maf unplugged, no change

The car has had a possibly related problem since before I bought it.. the cooling fan doesn't work right. The ground out from the ecm works fine and makes the relay operate ONLY if the fan is unplugged. If the fan is plugged in, the relay kicks on and off repeatedly and the idle races up and down. I tried another fan thinking that maybe the fan motor was drawing too much amperage, but no such luck.

My best guess at the moment is that the ecm (1226870) has bit the dust. I'm trying to get another one right now... hopefully before the car cruise this saturday.

Anyone have any suggestions on anything else i should try in the meantime?

 

well, I went out to fiddle with the car some more earlier. I turned the key and it started right up. I drove it up around my street and it ran perfect. I left it sit and idle in the driveway, it ran normal for about 20 minutes then died. I walked up to it, cranked it a couple times. Third time it fired back up and ran fine. I let it run for about an hour and a half and no problems. Kind of hard to pinpoint a problem when it won't stay broken.

 

what do the injectors ohm out at?

 

The best reading i could get from my crappy digi multimeter was 18-20 on all of them.

 

Time to call it a night (neighbors don't like the flowmaster). The car is running great at the moment, so... kind of hard to track down the problem 'til it acts up again. I'm going to try to go for a test run tomorrow when i can line up a ride home if it dies on me.

 

Spent the morning going through everything again. It started up and ran great, then a few minutes later it died out. Fired right back up. 20 minutes later, did the same thing. Went through and rechecked everything---wiring, etc--- I have 12v on the injector harness when it dies... it is definitely the ground out not pulsing. Found an ecm.. gonna take a few days for it to get shipped here. Hopefully thats the problem.

 

When I had a problem with the fuel injectors firing, it was the electronics in the distributor. Apparently, the dizzy sends a signal to the ECM to fire the injectors. For me, I bought an entirely new distributor. The car fired right up. I had lost 3 weeks in tracking down the root cause of the problem.

 

There is a reference wire that goes from the distributor to the ecm. I'm trying to find out how to test for signal on that, but it would most likely be something i'd need a scope for. I just borrowed a gm tech training book to start going through everything. So far everything i'm seeing in there still points to the ecm because I still have spark when the injectors quit getting pulse. My friend keeps telling me he thinks the 'quad drivers' in the ecm probably went bad. I'll find out soon enough.

 

Well... it *seems* like all is good now. I just got an ecm from the scrapheap, threw my prom in.. and it ran good for an hour. Also.. THE FAN WORKS for the first time in god knows how long. I'm gonna take it out for a test run tomorrow when I have backup to come pick me up if it dies.