1997 GMC Sierra 1500 Knocking/Loss of Power

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SeaFoam

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I saw this at Walmart, do you pour it in the gas tank ? Or the injectors ?

Did it happen all of a sudden?

Initial thought is either fuel pump or bad vacuum leak

I'd check those two first. Other simple causes could be an O2 sensor that cracked, or has a broken wire, or even a fricked up MAF sensor. Both of those would probably throw a CEL, but systems back then weren't always reliable


Eta: I swapped out the exhaust manifold on my 2500hd a few weeks ago, and forgot to hook up the plug wires for that side of the block. It ran (albeit like shite) with only one side of the block firing. Your truck can easily run on a dead cylinder. Some people wouldn't even notice. Hell, I've had mine run okay on two half-dead ones. It shouldn't be just one broken plug wire or bad plug IMHO

Eta #2: Looks like they used actual fuel filters back then. Start with swapping that out. It probably needs it anyway

If it’s shaking that bad could be....

Engine mounts busted

Spun a main bearing or harmonic balancer (unlikely but have seen it)

Check your driveshaft

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even a fricked up MAF sensor.

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If this is the problem you would also get a real strong smell of gas. Literally you would see your gas gauge move before your eyes.