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98' Tacoma 4x4 2.7L engine compression question

Discussion in '1st Gen. Tacomas (1995-2004)' started by harry44, Jan 18, 2016.

  1. Jan 18, 2016 at 2:55 PM
    #1
    harry44

    harry44 [OP] Member

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    Have an engine code that is on and off for the last couple years which is P301 and P300. took it to toyota to diagnose. they came back with low compression with readings cylinder1:40 PSI, Cylinder2:145 PSI, Cylinder3:80 PSI, cylidner4:75 PSI.

    Now here's my question, I'm not losing any power, any oil, or antifreeze. same gas mileage as always and idles perfect.

    what am I missing here? why is there visible or noticeable driving difference if my engine is barely fuctioning according tot eh compression tests?

    thank you for all your help!

    image.jpg
     
  2. Jan 18, 2016 at 2:59 PM
    #2
    KenLyns

    KenLyns 8.75" Third Member

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    So what did the shop tell you about what the codes said?
     
  3. Jan 18, 2016 at 3:04 PM
    #3
    harry44

    harry44 [OP] Member

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    Bad compression, that cylinders 1,3,4 were bad.
     
  4. Jan 18, 2016 at 3:11 PM
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    KenLyns

    KenLyns 8.75" Third Member

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    Wasn't aware the PCM can detect low compression, just misfires, by looking at the cam- and crank sensor rotation speed smoothness...
     
  5. Jan 18, 2016 at 3:24 PM
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    KenLyns

    KenLyns 8.75" Third Member

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    Got my hands on a service manual. P0300 is random misfire. P0301 is cyl 1 misfire, which does match up with the relatively lower compression in cyl 1. Not sure how much work the dealer tech did to eliminate the other possible causes of misfire (fuel, spark).

    When the check engine light came on, did you notice any roughness at that instant?
     

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  6. Jan 18, 2016 at 4:03 PM
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    harry44

    harry44 [OP] Member

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    no, and the engine runs perfect. same fuel economy and power levels and everything. they did a compression test at the dealership and that's where i got the compression readings from each cylinder.
     
  7. Jan 18, 2016 at 4:21 PM
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    KenLyns

    KenLyns 8.75" Third Member

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    ^Then just reset the codes and move on!
     
  8. Jan 18, 2016 at 8:26 PM
    #8
    CodeSeven

    CodeSeven LOC: 33.781461, -115.867251

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    you really shouldn't ignore low compression. youll want to find out where those 3 cylinders are leaking.

    good way to find out is to open your oil filler cap, open your radiator, remove your intake boot, remove the dip stick, remove the spark plugs, put a hose in the spark plug hole, put each cylinder at TDC as you check them (where all the valves are supposed to be closed), and start pressurizing each cylinder one at a time with a compressor.

    if you see bubbles or coolant coming out from the radiator, head gasket leak.

    if you hear air coming from the throttle body, intake valve leak.

    if you hear air coming out of the dip stick and/or oil filler cap, either a bad head gasket or bad piston rings.

    if you hear or feel air coming out of the exhaust, exhaust valve leak.

    if you pressurize cyl 3 or 4 and air comes out of the other cylinder, bad head gasket.

    Worst case scenario, you have to get your head cleaned at a machine shop. 180 or 240 or so depending on how detailed you want the machinist to go. it will probably be more since they'll have to do the valve clearances. which is not bad considering it will last a long time again.

    best case scenario, youre valves are just dirty with carbon and need to be cleaned since the carbon is preventing the valves from fully closing.

    another thing to think about. doing a pressure test slowly moves the cylinders, allowing for air to seep out in the process. your engine running compresses air in the cylinders much quicker, allowing less air to escape as it compresses. you saying your truck is running fine is kinda pointing to the possibility that the valves are just dirty and not closing all the way. plus excessive carbon in the system could mess with the p0420 monitors.

    I recently watched the "does it work?" videos on carbon cleaning and am stuck on seafoam. it seemed to work, either barely or really well against carbon buildup. I'd say do the liquid vacuum method into the PCV valve hose. thats probably the best way to assure that the seafoam will get to all cylinders.

    I myself used a bulb battery filler to extract the seafoam from the can and slowly injected it into my vacuum booster hose. though I now realize though that the vacuum booster hose may only connect to 1 cylinder as it is connected to only 1 of the galleries of the intake manifold. :facepalm:

    oh well live and learn. I think im going to do it again on thursday since I don't think I did it right anyways yesterday.
     
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  9. Jan 19, 2016 at 12:39 PM
    #9
    MrRiverMan

    MrRiverMan Compulsive tinkerer

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    Before I did anything else, I would go to the auto parts store and borrow a compression tester, then check the compression myself. With numbers as low as they told you, you should notice something in the drivability of the truck. I suspect those numbers might not be accurate.
     
  10. Jan 19, 2016 at 8:23 PM
    #10
    RustyVT

    RustyVT Well-Known Member

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    ^ what he said, if you've got a cylinder at 40 lbs you should be running at least a little rough.
     

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