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Problems with 95 GMC 1500


sdtom

Question

My truck has started acting up. The SES light comes on and it does not shift out of 3rd gear. The trans was rebuilkt about 6000 miles ago. Then the light goes off and runs great when the light is on the motor surges and if I step on the gas and get at 3500 RPM it drops to 0 rpm and goes right back up. I did the codes one time and all I got was the 12 code. I started it and it run great for about 20 miles then I started it later and the SES was on again. I got 4 codes this time they are 32 EGR 34 MAP 42 and 45 both Oxygen Senser. This has the %.7 liter motor in it does anyone have any Ideal what is going on?

 

Thank you in advance

Tom

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4 answers to this question

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Thank you for your feed back. I took to a shop down the street and they could not figure it out they said that it does not make any since as a electric problem should od anything to the trans. He could not get it to give any codes to work on two different scaners. I made a mistake this is a 94. Could the be the CEM that is causing this the truck will start and run just does not have 1st or overdrive and surges when it idels

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Codes on OBD-I vehicles I take with a grain of salt. Better to rely on old-school troubleshooting on those systems.

 

First, I'd be checking battery connections, and alternator output - anything with FI goes crazy with low battery voltage. Since your tach dropped to zero, I'd be looking here first.

 

Then check your cap and rotor - could be time for a replacement. If the wires are old, replace them too, and since you've gone that far, might as well replace the plugs.

 

Yank the primary power from the coil (plug with small wires), and crank it over - does it sound like it's skipping a cylinder? If the cranking sounds even and normal, you have decent compression. If not, further testing might be needed.

 

If that doesn't reveal anything, take a look at the spray pattern of the injectors. Easy to just pop the lid off the air cleaner and watch them as you rev and idle. If you see any dripping or any solid streams of fuel, they could probably use a rebuild or a new regulator.

 

If the truck runs great at idle, or part throttle cruise, but falls on it's face when you put your foot into it and won't rev above a certain RPM, your fuel filter could be plugged nearly solid.

 

Remember: fuel, air, compression, spark - check them all.

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Also check the vacuum hoses going to the EGR valve and MAP sensor. See if they are cracked/dry-rotted. I've had the EGR valve go bad on my 1995 Chevy Silverado K1500 350/5.7L a few years back, bought a new one, replaced it and been fine ever since. However mine idled and ran good, would through the SES light on everyday at the same spot on the road. Might want to pull down your glove box and check the main connector to the ECM (computer) and carefully reseat the connector.

 

Also check all that Jsdirt stated as well. He is correct, OBD1 vehicle don't monitor much at all or have that many sensors. Old school troubleshooting is a good idea.

 

Daniel

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I have had a couple of vehicles where the speedo would drop to zero. Also jump and bounce around around. Also they would have odd shift points. The problem was bad computers. What you can do is pull the computer out of the bracket and have it hanging. Then start the truck up. And slap the computer and see if makes any difference in the way the truck runs. Or have someone ride with you on a short trip. And have them slap the computer while you are driving. The problem is usually a bad soder joint or a crack board. And by slapping it cause an interment contact at the bad joint.

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