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Engine knock, no oil leak or loss on 1999 GMC Suburban 1500?

Wife came to pick me up at the airport, she has spent the last few months in Reno with my kids to try and help them "adjust" to college living. In reality, I think its her that needs the "adjusting" to not having her "babies" around.

Anyway, she comes to pick me up and I hear a knocking sound from the car. I ask when this started happening and I get the "I don't know" answer. Its fairly noticeable, so I'm lost how she couldn't hear it, even while driving.

Took the car into a local shop up here (don't know any of the shops) and they said they weren't sure what the sound was. Might have to pull the engine out and apart. That's going to cost about what the car is worth, so no.

I thought maybe a lifter, as when I checked the oil, it was low. After topping off the oil though, same sound still.

So I tried draining some of the oil and putting in a cleaner/lubricant called Sea Foam (I know, everyone is going to hate me for this). Then drained all the oil and replaced it and the filter. Still, same sound.

The knock seems to be tied almost directly to the rpms of the engine, except for one case. When you let off the accelerator, the knock speeds up excessively, then slows back down to match the rpms of the engine. So is this a valve issue then? And if so, wouldn't you think a local shop would diagnose this fairly quickly? Also, when driving, if under a heavier load, such as climbing a hill, the knock seems to lessen, almost to where I can't notice it.

Was thinking maybe trying a complete engine flush, but I've heard that can create more issues than it solves.

Also, knock seems to come from one side (passenger) more than the other.

Any direction is appreciated.

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Michael, any issues with the valvetrain would be more of a tapping versus a knocking. Concern here would be bad rods, main bearing etc. I'd start of with something as simple as a compression test and/or a leak down test. What size engine is in your Suburban, how many miles, type of transmission etc. would be good to know. Considered to place a sound recording on youtube or similar so we can hear what you hear?

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My bad I forgot to ad my bad I forgot to add this comment,, either one if he pulled the plug and it starts knocking or if it goes away that's a bad cylinder you looking for.. I apologize once again for not adding there…best of luck any advice needed email me…Danny the mechanic

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I inherited my Dads 1997 Chevy Suburban 2500. 454 engine. When I first got it last year oil was bad, so I changed it, started engine and it had a small knocking sound drove it, then one day 95% went away. Haven't drive it much for last 6 months. Then went to San Diego about 300 mile round trip everything was fine. Car sat for about a month, then went to start it and had that knocking sound again, but worse drove around block but did not go away. Parked it for about two weeks, changed spark plugs(NGK iridium), wires from Carquest 45.00. Cap and rotor from Autozone, the original cap and rotor were corroded, Started car, still had knocking,but maybe 30% better, drove around for about 15 mins., floored it 5 or 6 times, turned it off, A few hours later took wife to store and noise about 96% gone, engine sounds great has great power revs out quiet and smooth, scratching head but Happy, go figure.

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Whatever side u think the knock is coming from pull spark plug wire one at a time ..whichever wire you pull & the knock Stops that's the BAD CYLINDER…

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And My Bad for Not Adding that Trouble Shooting Comment,, if

it gets Louder Or Quieter /; Either One You found the bad Cylinder... Bearing Bad, or Wrist Pin?? A wrist pin knock is like a thud/ it's a Deep knock....My Bad for not Adding that Comment!! Best of luck.. need any more advice email me thank you!! Danny mechanic oronad71@gmail.com

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What if you pull spark plug from distributor and knock gets louder??

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Yes you just bout TRIED Everything?? What I would. Do get a Stesascope/ Ones that DR, USE 4 CHECKING HEART BEAT, Buy one if need 2! Start Engine WAIT till it Starts Knocking, START Listening with that Stesascope, Buy intake, valva. Covers, Timing Chain Cover, work Down too Oil Pan ,Final ✔ Check Torque Cover see if I hear anything ?? If All Else Fails keep it Running pull 1 spark plug @ a Time of you hear any Change of Knocking Sound that's the Cylinder that ur Problem coming From!! Good Luck Any Questions EMAIL ME! DANNY MECHANIC. ORONAD71@GMAIL,COM

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