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NEED HELP! 2000 GMC Sierra stalling/hesitation and surge


PalmTree97

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I recently purchased a 2000 GMC Sierra 1500. It was running fine until the other day when it stalled at a red light and the proceeded to hesitate on acceleration and then lurch forward. It keeps doing this. I have checked the fuel pressure, it was 50 psi and spikes at 55 when I accelerate, which I close to normal. I ran sea foam through the vacuum system to clean it. Also replaced PCV valve, replaced throttle position censor, replaced idle censor, and the fuel filter. Still stalls and hesitates and take a long time for the rpms to wind down. Any ideas?

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How many miles are on it? Just curious as to maybe a bad fuel injector. Not normal but they can go bad. Both banks running lean would point to an air leak most likely.

 

I had a code for each bank running lean but that was because I ran 100% E85 in a vehicle that wasn't set up for it. I expected as much but was just playing around with the E85.

It has 165k but I've already checked the injector and the fuel pressure. Everything seems to be fine mechanically as far as I can tell. I checked for air leaks with a smoker and I can't find any. Resetting the computer seems to have stopped the hesitation and stalling but I'm hesitant to say the problem is fixed.

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Good the light came on - that should give you direction.

 

Could be an ignition failure too, or maybe an intake gasket that let go while under high vacuum - lots of possibilities. I'm curious to see what the code is. May just be a misfire code, though. Would be nice if it's cylinder specific.

Code was reading lean conditions in both banks. I've smoke tested it and there are no vacuum leaks. It was reading lean when I first bought it and I found a cracked PCV line but I've already fixed that and there's no more leaking.

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Coils are good? Plugs? Wires? Injectors? Fuel pump? Regulator? All things to start first. Maf? Unmetered air after maf? Egr? Plugged cats? Bad o2 sensors? After you checked the basics....than go to leak down tests compression checks.

 

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Any smoke out the tailpipe when it's running rough? If it's clouds of white smoke, someone could've thrown some diesel in the tank by accident. Happens quite a bit these days. Also could've got a batch of bad fuel there - loaded with water or something. Another fairly common issue in repair circles.

 

That's par for the course with ethanol being used today. Why the government insists on this crap being in gasoline, I'll never understand. If I didn't know any better I'd say they're deliberately trying to make life miserable for us ... but I digress. :sick:

 

I'd try and get a sample of the fuel - get a clear container, disconnect the supply line to the injectors, and cycle the key a time or 2. Helps tremendously to have another set of hands there to help.

 

You'll clearly see if there's any water in it - it falls straight to the bottom in what look like bubbles, or blobs, that will roll around and change shape as you tilt the container. You might also see "streaking" through the fuel, like it's not clear - hard to explain. Either way that would mean you need to empty the tank and filter, and start fresh.

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Any smoke out the tailpipe when it's running rough? If it's clouds of white smoke, someone could've thrown some diesel in the tank by accident. Happens quite a bit these days. Also could've got a batch of bad fuel there - loaded with water or something. Another fairly common issue in repair circles.

 

That's par for the course with ethanol being used today. Why the government insists on this crap being in gasoline, I'll never understand. If I didn't know any better I'd say they're deliberately trying to make life miserable for us ... but I digress. :sick:

 

I'd try and get a sample of the fuel - get a clear container, disconnect the supply line to the injectors, and cycle the key a time or 2. Helps tremendously to have another set of hands there to help.

 

You'll clearly see if there's any water in it - it falls straight to the bottom in what look like bubbles, or blobs, that will roll around and change shape as you tilt the container. You might also see "streaking" through the fuel, like it's not clear - hard to explain. Either way that would mean you need to empty the tank and filter, and start fresh.

There's no smoke coming out of the tailpipe when I run it. I checked the fuel filter and it was in pretty good shape but I went ahead and replaced it anyways. One of my first thoughts was bad gas too but I was trying to test some other things before I drained 34 gallons of gas out. On my way to work today it hesitated and surged forward and actually threw an engine code for the first time so I'm going to get that read as soon as I get off.

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Good the light came on - that should give you direction.

 

Could be an ignition failure too, or maybe an intake gasket that let go while under high vacuum - lots of possibilities. I'm curious to see what the code is. May just be a misfire code, though. Would be nice if it's cylinder specific.

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Check that EGR tube with the smoker - they're a common failure point up here with the rust. Can't remember if that one triggers a code for both banks though.

 

Other possibilities that I think are more likely are a weak fuel pump, or a failed pressure regulator keeping the fuel pressure too low. I would expect to see in the 60's on a snap, and 55 psi at idle. These systems are super picky with fuel pressure -just 5 psi out of spec can and will cause problems.

After throwing a lot of parts and thoughts at it, I called a buddy of mine who's a mechanic. He told me to reset the computer and how to do it and now it's running a lot better with no hesitation or stalls. Still have the check engine light to deal with.

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How many miles are on it? Just curious as to maybe a bad fuel injector. Not normal but they can go bad. Both banks running lean would point to an air leak most likely.

 

I had a code for each bank running lean but that was because I ran 100% E85 in a vehicle that wasn't set up for it. I expected as much but was just playing around with the E85.

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how did you reset the computer

I unhooked the battery cables and turned the headlight switch on, then touched the cables together for about 45 seconds. Then I let it sit for about 20 minutes and then hooked it back up. After that it should forget everything so it takes about a day of driving it for everything to start feeling 100% again. Hope that helps. Ever since I did that the truck is running much better and the check engine light has gone off.

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Check that EGR tube with the smoker - they're a common failure point up here with the rust. Can't remember if that one triggers a code for both banks though.

 

Other possibilities that I think are more likely are a weak fuel pump, or a failed pressure regulator keeping the fuel pressure too low. I would expect to see in the 60's on a snap, and 55 psi at idle. These systems are super picky with fuel pressure -just 5 psi out of spec can and will cause problems.

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