Is 120 psi ok? Just starting engine few seconds

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by terramir, Feb 2, 2022.

  1. terramir

    terramir Member

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    Been having problems the engine been misfiring well the sparkplug on cylinder one looked really bad but that is where I had the misfire from the bad coils in the 1st place. He checked the compression and it was 120, after replacing the sparkplugs now the engine runs but I'm kinda worried that won't last long. After I replaced the coils it didn't last long. I know it's not a true compression test like this but maybe you guys could let me know if that is ok or not
     
  2. jdenenberg

    jdenenberg EE Professor

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    Divide 120 by 14.7 to get 8.16 as a compression ratio which is about right. Did you check all 4 cylinders?

    JeffD
     
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  3. terramir

    terramir Member

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    No Cylinder 1 was the trouble maker with the misfire the nasty looking sparkplug, I wanted to know if I could be dealing with a shot engine blown valves etc, but it seems to be all that misfire screwed up cylinder one so bad that the sparkplug was full of residue, question is could I have a blown head gasket or anything with this kind of compression. I'm gonna change my oil twice in the next few days, to get the sludge from two years of sitting around doing virtually nothing and then watch the oil religiously.
    I really need this car to run reliably for the next year or two. Honestly if I could find a low mile one I could swap my shield and cat to I would jump on the chance.
    terramir
     
  4. jdenenberg

    jdenenberg EE Professor

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    comparing cylinder 1 to the other cylinders would give you a hint about the compression.

    JeffD
     
  5. terramir

    terramir Member

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    True but the mech is not here anymore, I need to dig out my own compression kit and try it out can anyone tell me if I can check compression with tech stream to leave the engine off and do some kinda spinning mode that will tell me this without throwing the P0351 code
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    There is a "compression test" function in Techstream- I think it's in the engine section but might be hybrid control. Might want to force charge the HV battery to 7 bars first. It is quite "fiddly" to do it correctly- you have to follow the techstream instructions exactly. I did it once- I think it threw some kind of "no start" code anyway.

    Or, you can just check one cylinder at a time and run the engine at idle (1000rpm) for a bit. Leave the coil plugged in, put the spark plug in the coil and connect the metal end of the plug to metal on the engine (aka- ground). Or you can (carefully) push / connect a jumper lead from where the spark plug end goes in the coil to engine ground. The idea is to give the high voltage spark from the coil a direct connection to the engine.

    Then, with your compression gauge installed, start the ICE (turning the heater on high should help), hit the valve on the gauge to release pressure then let it build pressure and record the value. Repeat for each cylinder. Important thing is that all cylinders are fairly even. My gen2 had 130psi or so - at 700ft elevation. Higher altitude or lower baro readings will reduce the compression gauge results.

    Posted via the PriusChat mobile app.
     
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