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HELP! low compression on all cylinders

Discussion in 'Stock 1995 - 2001 Explorers' started by 1989dangeroustoy, March 2, 2012.

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    1. 1989dangeroustoy

      1989dangeroustoy New Member

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      I have a 96 explorer 4.0 ohv, today I did a compression test and got about 90 psi on all cylinders, I don't know if its bad rings, valves or timing chain, also I think I may have a cracked head, what do you guys think? Also do you think I'd be better off buying a used motor or rebuilding mine, I'd rather not pull the motor out and I definitely do not want to rebuild the bottom end
       
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    3. Dono

      Dono V8 Limited turbo and retired SC 4.0 OHV Elite Explorer

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      Low on all cyl? You sure your compression testers reading right? Run OK? How many miles on the motor? If it's really that low across the board, and mileage is high you might want To consider a complete rebuild or rebuilt motor.
       
    4. yavapaires

      yavapaires Active Member

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      My main question is; how did you check the compression? Did you pull all the plugs, or one at a time? Did you hold the throttle open, or closed? Improper procedure can affect the reading. If you have 90psi all cylinders, and the engine is running smooth, with good power, I wouldn't be too worried.
       
    5. my98nnj

      my98nnj Well-Known Member

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      Ditto above, plus the test is more accurate on a warm engine.
       
    6. DaExplorer

      DaExplorer Elite Explorer

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      Try testing one cyl and see the read. Then squirt some motor oil into cyl and re test. If pressure goes up I believe that it would indicate rings.

      Side note when you do restart it there will be lots of oil smoke. Neighbors won't like it. let it burn off before you hit the road or you could get stopped and cited.
       
    7. 1989dangeroustoy

      1989dangeroustoy New Member

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      I tested. It cold with all the plugs out and throttle
      Closed
       
    8. 1989dangeroustoy

      1989dangeroustoy New Member

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      I tested. It cold with all the plugs out and throttle
      Closed , motor has 143xxx on it
       
    9. 1989dangeroustoy

      1989dangeroustoy New Member

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      It runs but I have a cylinder 4 misfire
       
    10. steadyhand

      steadyhand Member

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      You need to check one cylinder at a time. You do not have to pull out all of the spark plugs while you test that one cylinder. Just unplug the coil to prevent the truck from starting. Do what DaExplorer said and put a tablespoon of oil into the cylinder and then immediately retest. IF the compression goes up with the oil in the cylinder, chances are your top oil ring is bad and your losing compression.
       
    11. yavapaires

      yavapaires Active Member

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      You will not get an accurate reading with pulling one plug at a time. However, I have done that to check a single cylinder. And the top two rings are compression rings. The lowest rings(three piece) are the oil control rings.
       
    12. 1989dangeroustoy

      1989dangeroustoy New Member

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      OK so I did get a lot better reading with the engine warmed up ,I got around 120 psi, but now I'm stumped. I checked the plug, wire, and coil, has decent compression , and i still have a misfire ,all that's left is the fuel injector or a small pissing coolant leak into the cylinder any other suggestions?
       
    13. steadyhand

      steadyhand Member

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      Maybe I'll learn something new here. Why will pulling all the plugs give more of an accurate reading than pulling one plug at a time? Each cylinder is independantly sealed and thus have the potential of giving a different compression reading on each one. How is pulling every plug to do the test going to make it more accurate?
       
    14. rjcooperss396

      rjcooperss396 Active Member

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      It doesn't make it any more accurate. It simply allows the other cylinders to bleed off pressure so that the engine turns faster and the reading is higher. I've never pulled all the plugs nor opened the throttle to do a compression test on any of my vehicles.

      The only thing you need to make sure of is that you do the same thing for each cylinder. Don't open the throttle for one but then don't for another. The thing you are checking is if all the cylinders are around the same.
       
    15. budwich

      budwich Well-Known Member

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      you probably need to give the forum more info on the misfire and checks that you have performed. Is it during cold starts, warm start, warm runs...etc

      further, did you swap plugs (cylinder to cylinder), like-wise wires, like wise coils (side to side)?????

      Further, what does the plug from that cylinder look like compared to others?
       
    16. 1989dangeroustoy

      1989dangeroustoy New Member

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      Its a constant misfire from start to operating temp, Cel throws a po304 cylinder 4 misfire, I got all new plugs autolite platinums. I checked the plug wire with a spare plug wire and a spark testing light, I swapped wire 3 and 4 on the coil pack all with no change, compression test was all cylinders around 120 psi, no coolant loss no excessive smoke, slight sweet smell if you put your nose close to the tailpipe but you really have to smell for it! All plugs looked the same and normal
       
    17. 1989dangeroustoy

      1989dangeroustoy New Member

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    18. bilzy7

      bilzy7 Active Member

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      I had p0304, it was just a bad plug, coil pack/plugs/wires... Maybe the plug socket(whatever it's called) has a problem. But p0304 is for crap... If I remember right cylinder 4? I know it is on drivers side.
      Google that code. I found so many other forums/sites with information on it. Goodluck.
       
    19. bilzy7

      bilzy7 Active Member

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      You confirmed correct gap on all plugs? .054 if I'm not mistaken or is that for the OHV engine...
       
    20. gonenuke

      gonenuke Active Member

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      Might be a plug bad out of the box, happens sometimes.
       
    21. Dono

      Dono V8 Limited turbo and retired SC 4.0 OHV Elite Explorer

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      Well, we have air, gas, compression, and spark to make the cylinder fire.

      Clogged injector maybe?
       
    22. drbenz

      drbenz Active Member

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      Or a large enough vac leak that only effects that one cyl., any hoses loose or broken?
       

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