1994 Chevy pickup will not go over 60MPH


Old 03-08-10, 03:05 PM
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1994 Chevy pickup will not go over 60MPH

Hi, I have a 1994 1/2 ton work truck, 4.3 with automatic(4 speed), 148,000 miles. Truck runs okay around town, but does hesitate an bog down at shift points, if I take it on the expressway I can take it up to 70, but then it starts to backfire, sounds like in exhaust, thought it was a plugged catylitic convertor and had changed out, but same problem persists after change. Any ideas where to look next. Do not see any kinks in fuel line. Thanks for any help.
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Old 03-08-10, 03:39 PM
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Just finished fixing something similar on my wrecker (5.7L Chevy) that turned out to be the ignition module. Mine wasn't quite as bad as yours. It would idle fine, but after warming up would stumble intermittently and also had some pinging and loss of power. I've had a run of things breaking lately; two weeks ago the E.G.R. valve took a dump.

Have you checked for codes? Very easy on the OBD-I GM stuff:

Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

All your routine stuff maintained? Plugs, wires, dist cap & rotor, etc?
Old 03-08-10, 03:53 PM
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1994 pickup

just bought truck, not throwing any codes, it I go to the auto parts store and plug in to check, might it show something without ever having flashed a check engine light?
Old 03-08-10, 06:09 PM
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You might try to look for sparking in the ignition, under the hood, at night. Makes sure any part of the secondary high voltage ignition components are clean of grime.

Things that come to mind that might cause are:

Cracked spark plug insulator inside the combustion chamber.

Carbon on spark plug(s) electrode area

Carbon on top of piston, where engine heat cause cylinder to fire at wrong time

Cracked and or carbon tracking on distributor cap.(IF you have a distributor)

Or grime at electrical connection areas of any high voltage secondary component

Coil breakdown

Out of time (could be something major or not)

Possibly something wrong in the valvetrain.

(These things quickly came to mind, and there are plenty more ideas out there I am sure.)

If you heavily accelerate then suddenly let off the gas, what happens? Does it back fire then at left off? How is the accelerating part?: Any bog, misfire, or stumbling?
Old 03-08-10, 08:49 PM
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How about a fuel filter??? or fuel pressure as in a pump going bad?? Just thoughts... Roger
Old 03-09-10, 04:29 AM
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Pump & filter also possibles; the list of candidates is pretty long as you can see from hopkins and ecman's posts. Last year I beat my brains out on a periodic random misfire that ended up being a worn distributor (shaft wobbled) and this last go-round with a failing module was no picnic either. The troubleshooting can be pretty frustrating.

It is possible to get a code and no light; on my wrecker transmission trouble codes will post but not light the light. I don't think anything that would cause what you describe would set a code and not light the light if it was a monitored item/system. Much of the ignition and fuel system are not directly monitored so wouldn't necessarily light the light unless they caused a condition that would light it. For instance, ignition coil, module, spark plugs, wires, fuel filter, fuel pump are not directly monitored, but if one of them causes a misfire or maybe an overly rich or lean condition you could get a light.
Old 03-09-10, 11:40 AM
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will go and check the timing and work my way from there, thanks for all the ideas....after that will check plugs, wires and cap.

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