99 Chev Silverado-Low compression

Discussion in 'Chevy Truck Forum' started by rockitman, Nov 13, 2007.

  1. rockitman

    rockitman Senior Member

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    #1 rockitman, Nov 13, 2007
    Last edited: Nov 13, 2007
    Took my 99 Silverado to the shop.Engine light stayed on.Truck ran slightly rough.Got a missfire code.Compression on #6 cylinder was 125 PSI. (5.3 L)
    Was told that the right cylinder head needed to be removed.Assuming the pressure was good on all other cylinders,would stll driving around hurt the truck?Would getting the pressure checked a couple times a year as long as the truck didnt run any rougher make any difference to the engine?Thanks for any help.Cost to repair: $1825.00 Canadian.:mad:PS,just bought the truck last week:eek:Passed safety with no codes or engine light.:confused:
     
  2. 75K30

    75K30 Senior Member

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    What does the book say a stock 5.3L engine should have? Cold cranking compression of a stock 10:1 engine of this size in a n average atmosphere of 14.7 should create just less than 150psi. This would mean that you may not recognize a very big difference in less than 25psi decrease.
    What were the other cylinders at, and are you getting other symptoms of a tired engine?
    Oil fouling that cylinder?
    Engine smoking?
    Lots of oil consumption?
    Blow by?
    I doubt any of these are actually happening, and you troubles are elsewhere.
    That misfire code could be a number of things, and may not be related to low compression. Heak, a small intakeleak could be the real problem, as could a dirty injector.
    I have been messing around with a toyota that is randomly mis-firing. Turned out to be a bad set of plugs.
    I would start by verifying that the vehicle is tuned correctly, and eliminate the simple stuff before, I got to excited about re-building a short block.
    By the way, I might be a little concerned if a mechaninc was actually willing to
    re-build one cylinder in a V8 engine.
    You gotta find the real problem.
     
  3. rockitman

    rockitman Senior Member

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    99 Chev silverado-compression 5.3L

    Sparkplug wires were swapped no# 4 & 6 and coil.Injectors were swapped.Compression still 125 psi-supposed to be 175 psi -10%.Yet truck -doesnt burn oil, smoke,shake.Slightly rough.Lots of power.Cant understand why the oil pressure gauge shows normal! No oil leaks.Run it till it gets worse?Then repair?:eek:
     
  4. 75K30

    75K30 Senior Member

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    Was the problem related to the plug wires? That is a little difficult to imagine since the LS"X" engines use individual coils per cylinder, and the harness that fires the coils can only reach the correct one. The same is tru for the spark plug wires and injector wiring.
    2 cylinders firing at thw rong time should have run terrribly, but hey, if that was the problem, and you believe it is alright, then drive the wheels off of it. I would not be too concernec about the lower compression. There could be a slight loss of power as a result, but not anything so great that you will notice.
    Just as a note, your oil pressure and compression are not related, since bearings and the pump determine pressure and is not related to the seal of the rings around the pistons.
    I think you will be fine for plenty of miles.
     
  5. rockitman

    rockitman Senior Member

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    Silverado 99

    Mechanic said I"ll have converter probs down the road.Could be a burned valve,etc-said it was mechanical.Tried cleaining it out & put air thru that came out the intake.Dont know what the normal compression should be.Trying to get someone to do a "sidejob".Apparently there was a problem for awhile.:mad:
     
  6. Chevy808

    Chevy808 Senior Member

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    Jus' curious.....what prompt you to do a compression test with a miss fire code?
     
  7. GMC004DOOR

    GMC004DOOR Full Member

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    I think mechanic is trying to get your money! Like 808 said what made a guy check comp. witha missfire code. i would be looking at plugs wires and coil packs(ignition system) not a problem that you have to take his word for and you cant see any physical evidence.IMO i dont buy it!
     
  8. rockitman

    rockitman Senior Member

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    Silverado compression

    The mechanic chose to do the compression to figure out the rough running & engine light.
    Trying to get a Chev tech to do a sidejob.Heard some do.Engine light stays on.Dont want to take chances down the road.But too close to Christmas to get the motor rebuilt.Especially when l just bought the truck a week ago.:mad:
     
  9. rdillon

    rdillon Full Member

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    Not to be a idiot.... Squirt some oil in the cylinders questioned that will boost compression. If codes still go off. Take off the rocker covers and check the lash. May be a stuck lifter.
     
  10. rockitman

    rockitman Senior Member

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    99 silverado compression

    The mechanic put cleaner down cylinder-compresssion moved from 125-130-lbs.Engine light seems intermittent now.:confused:
     

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