Rough Idle

2007 GMC SIERRA
236,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC
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CAMPORTER13
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  • 4 POSTS
My truck was running fine, then it lugged a few times then did not lug. Eventually it did not quit lugging. The idle was bad but in reverse or drive it was worse. It shook the truck. As far as acceleration I would compare it to when a vehicle runs hot and goes into limp mode. It does however have enough power to get on up and get to speed. At driving speeds it is fine. I took it to the shop, they replaced plugs and wires and said I have a cylinder that is out. I got it back and decided to drive it rather than putting a new motor in it. I was driving and a puff of smoke came out (blueish if I had to say). Then the truck ran fine, no issues, the engine light stopped flashing and actually went off. It ran great for about a day, Then it went back to its old ways. I had to juice it the next day and once again a puff of smoke and it was fine. As for now if it is running bad I stomp on it and smoke and great again.

The mechanic also said my compression was like 25 psi. I am hoping for the best but prepared for the worst.

Thanks
Nov 14, 2018 at 7:15 AM
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ASEMASTER6371
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Good morning.

25 is very low. That is your issue. The question is why.

A burned valve will not fix itself and run good then bad. Same with a piston.

It may be a valve lifter that is sticking pumped up and not allowing the valve to close. That can be confirmed by removing the valve cover and watch the valves move while running. You just need to remove the side with the issue. Number five is the third cylinder back on the driver side of the motor.

If it is a lifter, that is still a major job as the head has to be removed to replace the lifters. If you are going to do one, you should replace them all.

Also, while the head is off, the cam lobes need to be inspected for damage. It may also be a camshaft worn out causing damage to the lifter.

Roy
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Nov 14, 2018 at 7:46 AM
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CAMPORTER13
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As far as driving it as is, rather than sinking more money into it. What do you think? Can it be driven? As far as the cylinder, the mechanic said Number two was out. When I ran the codes before it said bank 2 was lean and engine misfires. But after the smoke the engine runs fine and the engine light goes off. What is the cheapest way out? Thanks
Nov 14, 2018 at 10:01 AM
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ASEMASTER6371
  • AUTOMOTIVE REPAIR CONTRIBUTOR
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I am sorry, there is no cheap way to fix this without determining the cause first. The tech needs to put shop and look at the cylinder and find out why it has low compression. Then he can tell you exactly what the issue is.

I am afraid this is going to be a costly repair no matter how it turns out. Please let us know how much it cost and what is wrong.

You can drive it but the more you drive it, it may be damaging the engine more.

Roy
Nov 14, 2018 at 10:45 AM