GMC problems
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Joined: Oct 2002
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From: The Big, Oregon
GMC problems
Not a Ford, but I have to make it run anyways. It's a 94 GMC W4 Forward (isuzu built) with a 350 and 4L80E. On Thursday or Friday, the driver came in complaining it lost third and fourth gears, it just had first and second. The other mechanic/driver took the truck out and confirmed it, brought it back, and shut it off. The truck has not been able to start since. It will crank all you want, no fire, no spark, no injector pulse. I put the code reader on it, all I got was a code 12, no reference pulse. I checked the ignition module, got a solid .5v ac out of the pickup coil when cranking, unplugged and cleansed every connector between the distributor and the computer, all with the same results. The only thing I can think of is the computer went, and that might explain the loss of third and fourth, maybe as a limp-home mode. Anybody have to deal with something like this, have any insight?
Lead Driver
Joined: Feb 2003
Posts: 8,140
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From: Oak Harbor, OH
Jared what's the transmission doing?? Hitting third and freewheeling? The no start is probably a computer issue. Is it possible that the ignition module has puked? Just because it's within voltage specs doensn't mean it's working.
Post Fiend
Joined: Feb 2003
Posts: 6,940
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From: Eastern WA
Originally Posted by Ford_Six
Would this have a crank position sensor? It has TBI and a distributor.
Last edited by CowboyBilly9Mile; Jan 16, 2006 at 12:47 AM.
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Joined: Oct 2002
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From: The Big, Oregon
From what I was told, the transmission would shift from first to second, then hold. Not even an attempt to hit third or fourth. This thing is driving me nuts, it almost sounds like it went fail-safe, but it still had first gear, and had decent power. I had the ignition module tested at the parts store, they checked it at ambient, cold, and hot, it checked out ok.
Does the ignition module send a signal to the computer, or does the computer directly use the pickup signal to trigger the module? Does anybody know what wires these would be on the computer plug?
Does the ignition module send a signal to the computer, or does the computer directly use the pickup signal to trigger the module? Does anybody know what wires these would be on the computer plug?
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Joined: Dec 2005
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is the distributor turning??
maybe what drives the distributor isn't.
I dont think a 94 GM with throttle body had the fancy crank and cam position stuff on it, just depended on distributor to tell ECM where it was.
maybe what drives the distributor isn't.
I dont think a 94 GM with throttle body had the fancy crank and cam position stuff on it, just depended on distributor to tell ECM where it was.
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Joined: Oct 2002
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From: The Big, Oregon
Made some progress on the thing today, it runs now but not very well, and won't start without a shot of carb cleaner or ether. The computer isn't firing the injectors while cranking, but once the key is at run it's ok. The idle is really high, it's probably got a vacuum leak, but I'm trying to fix one problem at a time. Fuel pressure is ok when the pump is on, but the regulator is leaking by after shutdown, it drops to nothing pretty quick. I deadheaded the pump with a gauge on it, and the check valve held. The regulator had a kit put in it, and still did the same thing, so I'm kinda at a loss on that.
Is there a wire that goes straight from the ignition switch start position to the computer, telling it to fire the injectors? Does the ignition module go into some sort of stand alone mode at this point?
Is there a wire that goes straight from the ignition switch start position to the computer, telling it to fire the injectors? Does the ignition module go into some sort of stand alone mode at this point?
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