Help with GMC 3500
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Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
Help with GMC 3500
In my defence, its not my truck Lol.
Was just wondering if anyone knows a good forum for late model GMC pickups.
My dad's 1993 GMC seems to have gone into failsafe mode (4L80E tranny).
Was just wondering if anyone knows a good forum for late model GMC pickups.
My dad's 1993 GMC seems to have gone into failsafe mode (4L80E tranny).
Posting Guru
Joined: Mar 2005
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From: KY
David, I am not an expert of those trans. I know the 6.5's pretty well.
Most trans, no matter who makes them, operate an fail the same way. They are more similar then you may think. Make the same checks as you would with your trans.
Most trans, no matter who makes them, operate an fail the same way. They are more similar then you may think. Make the same checks as you would with your trans.
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Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
You're probably right catfish, but I'm not sure if his truck is OBD1 compatible (should be), so I'm not sure how to retrieve any fault codes. That would be the first test to run. I suspect that I reset the computer when I disconnected connector at the trans because it worked for a day or so before reverting to hard/late shifting.
I usually prefer to do a few good days of research on any new vehicle I work on before I touch the first bolt.
I usually prefer to do a few good days of research on any new vehicle I work on before I touch the first bolt.
Junior User
Joined: Jan 2008
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From: portsmouth n.h.
smart move guy, but have you checked the fluid, we had a gmc 3500 at work that we beat the crap out of and i mean beat the crap out of it, well to make a long story short, doing a delivery one day just a couple of tires nothing over 50 pounds, takin it easy, shifting nice and smooth, all of a sudden hard hard shifts, like the next gear wasnt there, and sometimes not shifting at all. checked the computor, nothing, dropped the pan and a handful of shavings littered the magnet, related to the beating i dont know. but shaved a couple gears and the park pin, a 1600.00 oops fell on my lap
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Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
Fliud was the first thing I checked and it is at the correct level, smelled pretty good too. My dad does not abuse any of our vehicles, hardly ever even tows with the truck. haven't dropped the pan yet because I would rather get some clues from the PCM first.
$1600 for an overhaul? sounds like you got off easy!
$1600 for an overhaul? sounds like you got off easy!
Post Fiend
Joined: Jan 2005
Posts: 8,402
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OBD 1. If you look under the dash, probably just to the right of the steering column, you should find the diagnostic connector. It is a wide thin plug with a verticle rib on the top edge. Using a paper clip or similar, bridge the two side by side terminals on the top right, the SES light will then blink out the codes. You can try truckforum.org for GMC.
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Lead Driver
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Elder User
Joined: Jan 2008
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From: Guymon
You might be able to go to autozone and they can probably hook up their reader. It will be the ALDL connection (obd1 format) right under the steering wheel colum. You can also short out 2 pins on the ALDL connector and it will flash the codes on the dash but Im not sure which ones it is. The hayns or chiltons manual will probaly show which ones to jump. Wal-mart also sells a little ALDL plug that will jump the correct wires when you plug it in. It even comes with a book with all the codes in it.
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Lead Driver
Joined: Nov 2003
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From: Campbell River, B.C.
I managed to find the info on how to use the "paper clip" method. Worked great. I did get two error codes, (TPS and speed sensors) but, I have a feeling it might just be a case of bad grounds. It's working properly again, so I'll just have to keep an eye on it.
Guess I won't have to sign up on a chevy forun just yet!
Guess I won't have to sign up on a chevy forun just yet!
Posting Guru
Joined: Mar 2005
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From: KY
That is where I was going with your checks. No matter who makes the trans or engine or whatever they work the same. They have to have speed signals, pressure signals, temp signals and position signals. You are probably right about the grounds. I have made allot of money by cleaning connectors and grounds and fixed problems. When you have several current faults on any computer controlled component the problems will most likely be connected and ground are a very common problem. Good luck with it.
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Lead Driver
Joined: Nov 2003
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From: Campbell River, B.C.
Well catfish, it looks like your right, I've dealt a few ground problems before too. Really bazzare symptoms in some cases . I found 3 grounding points at different corners of the engine, and 2 had obvious signs of corrosion thanks to minor coolant leaks (but lets not go there!!). Oh well, he still likes the truck, so I guess I'll have to be nice to it.
Its unbelieveable how many new problems the electronics can cause. Man, am I ever glad I drive an old mechanical diesel. I really shudder to think what is in store over the next few years in diesel technology. The GMC is also mechanical other than the tranny.
Its unbelieveable how many new problems the electronics can cause. Man, am I ever glad I drive an old mechanical diesel. I really shudder to think what is in store over the next few years in diesel technology. The GMC is also mechanical other than the tranny.
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Lead Driver
Joined: Nov 2003
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From: Campbell River, B.C.
Yes. 6.5 turbo, without the ECM controlled injector pump. Not really sure if this was even available from factory, but it was a former dealer service foreman's truck.
Posting Guru
Joined: Mar 2005
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From: KY
The only mechanical 6.5's that I saw in that year were in medium duties like box trucks. It was an emissions thing. That doesn't mean they didn't make them.
The later 6.5's weren't bad motors. When they put cooling jets on the pistons that helped them out. I have seen allot of miles on them.
Their head gasket problems were the same as the 6.9's. Bad gasket design that was fixed.
They just about all cracked between the valves but I only ever ran into one that got into the seat and caused a problem.
Now I have seen allot of driveability problem with them that ended up being the converters in the exhaust. Also beside the pump, {electronic} ,problems they would have waist gate problems. It was either a bad solenoid or the vacuum line that ran from the pump to the solenoid and then to the gate would get hard and break and leak the vacuum. Sometimes they would set a fault and then sometime they wouldn't.
They really weren't bad ole motors.
The later 6.5's weren't bad motors. When they put cooling jets on the pistons that helped them out. I have seen allot of miles on them.
Their head gasket problems were the same as the 6.9's. Bad gasket design that was fixed.
They just about all cracked between the valves but I only ever ran into one that got into the seat and caused a problem.
Now I have seen allot of driveability problem with them that ended up being the converters in the exhaust. Also beside the pump, {electronic} ,problems they would have waist gate problems. It was either a bad solenoid or the vacuum line that ran from the pump to the solenoid and then to the gate would get hard and break and leak the vacuum. Sometimes they would set a fault and then sometime they wouldn't.
They really weren't bad ole motors.