Edmunds Answers



  • sandman235 03/04/08 5:17 pm PST

    first find out why the low compression, a cylinder leakage test or wet compression test will tell if it is a valve, rings, or blown head gasket, if the rings are bad the engine will need to come out and depending on what he finds a long block might be the cheaper route to take. sorry

  • kiawah 03/04/08 5:32 pm PST

    I'd probably have them take the heads off, reasonable chance it's a blown head gasket, or even valve problem.....which means you don't have to replace the engine, just some engine work on the top end.

  • loosenut 03/04/08 7:59 pm PST

    --how to determine whether a low compression problem is rings or valves..
    index all spark plug wires,so you can put them back the way they are supposed to go..usually, make sure they are in the wire looms correctly.
    -2--pull ALL the plugs-this way you can count how many times the engine turns over..4/5 times is usually enough..
    -3--check compression "dry"..without adding anything to the cylinders..while all the plugs are out,go ahead and check all the cylinders..usually a good cylinder should produce near 100 psi,depends on kind of motor,
    --4--the cylinder with low compression-take and squirt a tablespoon or so of motor oil in the cylinder-easily done with a foot of vacuum-size-hose-small enough to fit in spark plug hole..dip it into quart can as far as you can-put your thumb over the end-put other end in cyl - this will temporarily seal the rings,and will raise the compression..
    --5-- if this raises the compression-this means the rings are bad,and need to rebuild the motor...if it DOESN'T raise the compression,you have a valve that is leaking and might get by with having the heads reconditioned ..i agree with the other poster, you might be better off, and save coin by installing a long block, as everything inside has been reconditioned and you get a warranty! Either way, it's not gonna be cheap! Were you pulling a boat up a hill?,or did it leak out the coolant? Usually,you have to work a engine pretty hot to burn a valve or rings..I've even seen a hole burnt in pistons, mostly while out in California, where LA drivers would try to climb the hills going to Las Vegas in 100% heat-in high gear with the a/c on cause they were hot..well, by burning up their motor, and not downshifting, and turning off the ac while climbing a hill-they ended up a lot more uncomfortable-when they broke down - in 100° heat-in the desert!..we get spoiled with automatic transmissions and a/c,we can forget that some conditions require some skill.


  • joecoolone 04/23/08 11:21 am PST

    There is a service bullitin refering to leaking intake valves. I have an 04 with 76000 miles, cylinder 2 misfiring. Just found out yesterday.


  • eotto05 05/16/11 4:39 pm PST

    i have the same problem with my 05 trailblazer LS just bought three weeks ago from a small lot and he guy that sold me the truck has been giving me the run around ever since i thought it was plugs (nope) then the coil pack (nope) not sure what it could be but my truck if i was to let go of the brake while in gear it tugs, vibrates and the dome lights somewhat flicker dont know if thats a proplem but would like to here more if anyone has any info please post thank you


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