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5.7l Vortec; Severe loss of power

coloradofarmboy

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coloradofarmboy Enthusiast

coloradofarmboy

Posted
Posted

Info on truck is in my signature, has about 190,000 original miles, engine never rebuilt. Here is a long run down of what is going on, with every detail I could think of, please give it a all a read and tell me what you thing:

 

I was driving on Friday night with some buddies. Truck had been working great, no problems, hadn't been abusing it or asking too much of it at all. Came up to a stoplight, and decided I would see how fast I could accelerate. Stomped the accelerator, and the engine bogged down and accelerated very very slowly. This happened a few more times that night when I just tried to accelerate at a normal speed, but I accelerated very slowly with very little power, however every once in a while it would accelerate and perform normally.

 

After babying it all the way home at acceleration speeds slower than my miniature donkey, I played around with it a little bit in the driveway. The truck seems to have somewhat normal speed/acceleration in reverse, but in drive, 3,2, and 1 it has that power/acceleration problem.

 

Next morning, I had forgotten the problem was there and took it out to go run errands. Performed normally for about 10 minutes of driving, but then I stopped at a light, light turned and I had horrible acceleration and no power. Pulled over on the side of the road because the cars behind me were not very happy that I was driving so slow, looked around the truck for anything obvious; no leaks, no smells, no smoke, etc... I ended up playing around with the PRNDL for a while. When it is in park/neutral and reverse the engine sounds normal and revs just fine, but not in drive. After playing around with it, all of a sudden it started accelerating fine again. Got to the grocery store and parked, came out about 15 min later and it was at it again with the symptoms.

 

I figured I'd throw this in, when the truck is having trouble accelerating, it sounds like it would if I was pulling a trailer that was a little too heavy for the truck. To give you and idea of how it feels, imagine dropping a Prius motor into an F-250; thats what it feels like; too little engine for too much truck almost.

 

I babied it home again, and right away got to looking for a cause. At first I thought I might have gotten a bad tank of gas from Valero on Thursday, but now that I think about it im not so sure. Anyways, I went on to set the programming back to stock with the Hypertech, didnt change a thing, reprogrammed as carefully as possible, didnt change a thing. Then I called GMC Service Dept. and they said it could be anything from a bad fuel filter, bad fuel pump, to clogged injectors, but they seemed pretty certain it was a problem with the fuel system. Then I went and got some SeaFoam and a new fuel filter. I split the SeaFoam into thirds, 1/3 in the tank, 1/3 in the crankcase, and 1/3 in the vacuum line, just to cover all bases. Blew minimal amounts of white smoke, took it for a drive and it was at its worst as far a no power. Can't even get up the slightest inclines without having to back up as far as possible, floor it forward, get up to 5mph if im lucky, and I got it back home again. Then I checked the K&N, no blockages, didn't have time to check the throttle body, I will do that tomorrow. I did not put on the new fuel filter because I figured I would let the 1/3 bottle of SeaFoam sit in there overnight then run it in the morning to try and get as much crap, if any, out of the tank/ fuel system without dirtying a brand new filter.

 

If you have read all of that, I thank you. This truck is my baby and I want to find out what is wrong. She cant even get up and over the 2" bump that is at the entrance to my garage on her own. What is going on? Fuel system problems? Driveline problems? (there is no abnormal noise from the tranny) All the fluids are in good condition and full. Any help would be appreciated. Thanks! T.J.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Change the fuel filter. Took you longer to type that post than it would take to change the filter.

coloradofarmboy Enthusiast

coloradofarmboy

Posted
  • Author
Posted

Change the fuel filter. Took you longer to type that post than it would take to change the filter.

 

I just changed the filter and drove it around a bit. Problem is still there; when i start it up cold and start driving it drives relatively normally for about 2 miles, then it bogs down and loses power.

Duelin Enthusiast

Duelin

Posted
Posted

Check the MAF sensor. They have a tendency to get dirty with the K&N Systems. Also check you Cat converter if you still have it.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Easiest way to check convertors is to drop the exhaust. With the vehicle in park, try to rev engine as it is now. Then disconnect the exhaust and try it again. Does it behave differently? A plugged exhaust will generally show up under any acceleration more than light. In other words, if you gradually accelerate the vehicle will accelerate, but, if you try to accelerate harder, the engine will just fall flat. As you let up on the gas, it will start to accelerate.

You could also tell by feeling the exhaust coming out the tail pipe as someone tries to rev the engine. The exhaust will just not flow much and will be pretty quiet if convertors are plugged.

 

Note that a fuel injected vehicle will behave the same way if the fuel filter is plugged, or the fuel pump is starting to fail.

Folically Challengjed Enthusiast

Folically Challengjed

Posted
Posted

When was the last time the plugs and/or wires were changed?

 

I had a '96 Sierra (though with the smaller V8) that would dog down horribly unless I carefully feathered the throttle. I thought it was a tranny issue, but the mechanic threw on a new set of plug wires, and it was right as rain.

 

Just a thunk.

 

FC

  • 1 month later...
coloradofarmboy Enthusiast

coloradofarmboy

Posted
  • Author
Posted

Problem solved. Transmission blew. The previous owner had tranny replaced, the shop that did it put a 95' transmission in and not a 96'. slight misalignment over time caused the tranny to go out

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

i thought it sounded like a gear finding concern ,and misalignment cant happen ,so IDK what ya mean lol

 

what are ya gonna put in it ,,,FYI ,GMs trannies have a 3 yr warranty

 

if ya rat bag the lifted truck ,get a perf tranny.....god i hate lifted trucks lol!!!!

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