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4.3 looses power

4.3 looses power

Postby atxltz [OP] » Oct 08 2012, 12:30am

I've got a 92 GMC 1500 V6. Starts and runs ok. Sometimes after idling for a few minutes, the idle goes up and down-so far down that it almost dies. While driving-cruising- it feels as if it starts to drop cylinders and loose power. If you punch it, trans down shifts and it wakes up and goes. Currently no CEL.
Here's what I've replaced so far:
IAC valve
rebuild TB
plugs
wires
cap & rotor
fuel filter
fuel pump
TPS
Ignition module in distributor
new gas
gas treatment
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Re: 4.3 looses power

Postby lzn197 » Oct 09 2012, 2:35pm

Whew. Pretty old truck. Have you done any tests to see if the engine is in good, mechanical condition? Compression check,cylinder leak down check, timing chain check? Fuel pressure?

My first "wild ass swag " guess, assuming all of the above are ok is a problem within the distributor or a MAP sensor. Hope that helps.
Gordon
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Re: 4.3 looses power

Postby atxltz [OP] » Oct 10 2012, 5:23am

Yeah, the engine is in good shape. It was all good and then all of a sudden this problem started out of the blue. Fuel pressure is good and was good before the new pump went in. I would think compression, timing or vacuum leak but this doesn't happen all the time. It's weird, most of the time it acts up but on a rare occasion it will run just fine leading me to believe it's an electrical problem-sensor related.
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Re: 4.3 looses power

Postby lzn197 » Oct 10 2012, 1:52pm

I wish I had a dollar for every time somebody ran NO tests on an engine and said "yeah...........the engine is all good". A 1992 truck can have a LOT of miles and time on it and you have to be sure the engine mechanical is good. You aparantly totally ignored my comment about the MAP sensor which by the way IS a sensor.
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Re: 4.3 looses power

Postby atxltz [OP] » Oct 11 2012, 3:27am

I don't want to get into a pissing match with you. I've done a compression test. All cylinder are with 10% of each other, around 130lbs. I've done a cylinder leak down test, all valves tested good. Fuel pressure is at 11psi. I'm very aware that the MAP sensor is a sensor. You can keep your "wild ass swag" guess to yourself and I'll wait for the next guy, thanks anyway.
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Re: 4.3 looses power

Postby lzn197 » Oct 11 2012, 10:28am

Ok. Good luck.
Gordon
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Re: 4.3 looses power

Postby atxltz [OP] » Oct 25 2012, 6:17am

update:
Changed MAP sensor with little change. Did notice that the lights dimming while engine surging. Checked alternator output and got 12.9v at idle and when idle dropped while surging as low as 9v. A buddy loaned me his 105amp alternator and the problem seemed to stop. Only when I turned lights on and or a/c ,the problem would sneak back. When the gauge would read a substantial drop, the surging came back only to smooth out after all loads were turned back off.
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Re: 4.3 looses power

Postby GarrettCobb » Oct 25 2012, 10:36pm

sounds like it could be an electrical issue in deed
especially if the voltage is droppng, maybe its a ground of some sort and cause little flow or something is slightly shorting out.
idk what else to tell you buddy :/ hope you get it figured out soon.
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Re: 4.3 looses power

Postby Lunchmeat » Oct 25 2012, 10:50pm

What about the battery and alternator cables?
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Re: 4.3 looses power

Postby atxltz [OP] » Oct 26 2012, 1:18am

Checked all the wiring from battery to alternator-good. Ground cable and ground strap tight and secure. It think this truck has more than one issue. Still while cruising, it looses power like it's loading up.
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