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Compression PSI in 2010?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by PlumbersCrack, Oct 7, 2015.

  1. PlumbersCrack

    PlumbersCrack Junior Member

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    Did some searching around here and on the net but not finding what the compression is supposed to be for these motors. I read up on some Gen2 threads and their readings were from 135-150PSI per cylinder.
    Each Cylinder I did twice
    Cylinder 1 - 118 - 118
    Cylinder 2 - 126 - 121
    Cylinder 3 - 120 - 118
    Cylinder 4 - 118 - 125

    I really hope there are within the norm but guessing they aren't. They are all pretty close to each other.
    Thanks.
     
    #1 PlumbersCrack, Oct 7, 2015
    Last edited: Oct 15, 2015
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Wondering just how you'd perform a compression test on a Prius, with it's somewhat unique start up, I looked up this: covers several inspections, including a compression test. Maybe it'll help:
     
  3. PlumbersCrack

    PlumbersCrack Junior Member

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    I went ahead and removed the plugs and hooked up my regular compression tester and did things as normal. Hooked up, turned the car on and let it try and crank/start when it first turns on to warm up the cat. Motor auto shut off after about 6 seconds and then recorded the highest number it reached. I did this for all the cylinders to try and get a baseline. I will take a look at the guides you sent me, even though I won't be using a touchstream, so thank you for that. I also plan on performing a leak down test a bit later today to see if its a big leak, maybe in one or more spots, and if I should just get another motor, heh.

    Thanks again.
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Here's a cut-and-paste from the pdf:

    INSPECT COMPRESSION
    (a) Put the engine in inspection mode .
    (b) Warm up and stop the engine.
    (c) Remove the 4 spark plugs .
    (d) Inspect the cylinder compression pressure.
    (1) Insert a compression gauge into the spark plug hole.
    (2) Connect the Techstream to the DLC3.
    (3) Turn the power switch on (IG).
    (4) Turn the Techstream on.
    (5) Enter the following menus: Powertrain / Hybrid Control / Active Test /
    Compression Test / ON.
    (6) Fully depress the acceleration pedal.
    (7) Depress and hold the brake pedal, and turn the power switch on
    (READY).
    NOTICE:
    The measurement must be done as quickly as possible.
    * Noise may emit from the transmission. However, this is not a
    malfunction.
    * Always use a fully charged battery to obtain an engine speed of
    200 rpm or more.
    Standard compression pressure:
    1373 kPa (14.0 kgf/cm2, 199 psi) or more
    Minimum pressure:
    1079 kPa (11.0 kgf/cm2, 157 psi)
    Pressure difference between each cylinder:
    98 kPa (1.0 kgf/cm2, 14.2 psi) or less
    * Inspect the other cylinders in the same way.
    * Measure the compression as quickly as possible.
    (8) If the cylinder compression is low, pour a small amount of engine oil
    into the cylinder through the spark plug hole, then inspect it again.
    ?? If adding oil increases the compression, the piston rings and/or
    cylinder bore may be worn or damaged.
    ?? If the pressure stays low, the valve may be stuck or seated
    improperly, or there may be leaks from the gasket.
    2010 Toyota Prius Repair Manual
    (e) Install the 4 spark plugs .
    NOTICE:
    After performing all the procedures, be sure to clear DTCs stored in memory. Then, check that the normal system code is output.
    * Inspect the other cylinders in the same way.
    * Measure the compression as quickly as possible.
    (8) If the cylinder compression is low, pour a small amount of engine oil
    into the cylinder through the spark plug hole, then inspect it again.
    ?? If adding oil increases the compression, the piston rings and/or
    cylinder bore may be worn or damaged.
    ?? If the pressure stays low, the valve may be stuck or seated
    improperly, or there may be leaks from the gasket.
    2010 Toyota Prius Repair Manual
    (e) Install the 4 spark plugs .
    NOTICE:
    After performing all the procedures, be sure to clear DTCs stored in memory. Then, check that the normal system code is output.



    My take is Techstream is needed. Not sure that it's a necessity, seems like there's a lot of work arounds, even the Repair Manual often offers with/without methods. But not sure in this case. Seems to me if you were to do step 6 WITHOUT step 5 it'd be hells-a-popping time, lol.
     
    #4 Mendel Leisk, Oct 8, 2015
    Last edited: Oct 8, 2015
  5. CR94

    CR94 Senior Member

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    Any chance the low pressures could be due to throttle being closed due to not doing Step 5? That wouldn't have been a problem in the days of mechnical accelerator-to-throttle connections, but throttle-by-wear creates new wrinkles.
     
  6. PlumbersCrack

    PlumbersCrack Junior Member

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    It's quite a possibility. I went ahead and tried turning on the car and just revving the damn thing and my numbers never really got much higher than what I originally experienced. I was NEVER able to into the 135psi range but its quite possible that the techstream is needed.
     
    #6 PlumbersCrack, Oct 9, 2015
    Last edited: Oct 15, 2015
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    Just looked up leak down test a bit. Since this is run with the engine off seems it'd work without issues due to the hybrid factor. Will you raise the piston to TDC on the cylinder you're testing? I'd assume you can get a socket on the crankshaft through the passenger side wheel well. Be really interested to hear how the test works out.
     
  8. PlumbersCrack

    PlumbersCrack Junior Member

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    That's my plan. I really want to get this thing fixed up. The other two seemed to be okay but when I ran about 50-70psi, I can really hear the air coming out from the oil intake. Exhaust, Air intake, coolant and PCV all quiet and no noise/bubbles, AKA most likely my rings are jacked.
     
    #8 PlumbersCrack, Oct 9, 2015
    Last edited: Oct 15, 2015
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  9. Rocky Mountain Priusman

    Rocky Mountain Priusman Active Member

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    Any update on if Techstream is actually needed for this job? Hoping to just buy a compression gague from local hardware store and do this quickly on my own. But if its a waste of time without it I will go through the process of figuring out how to aquire techstream.
     
  10. ChapmanF

    ChapmanF Senior Member

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    Compression tests are generally done with the throttle wide open and the engine cranking at around 250 rpm (the speed you typically get with a normal starter motor).

    In Techstream there is an option to make the engine do that, so you can complete a compression test. That is never how the engine behaves in normal operation.
     
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    Leak down test is best. A competent garage can do this, figure out if head gasket is failing, and how.
     
  12. Rocky Mountain Priusman

    Rocky Mountain Priusman Active Member

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    Oh the perils of living in a small town... I took my gen 2 prius to one of the only mechanics in town that supposedly worked with Toyotas. He said "ive never worked on a hybrid before, do you like it?" and proceded to ask me very basic questions about how it works...
     
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  13. Mendel Leisk

    Mendel Leisk Senior Member

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    That shouldn’t impede his ability to do a leak down test. The car is not even running. He basically needs to pull the plugs, turn the crank, connect the leak down valve set and apply compressed air. He will be able to determine which cylinder is leaking, and how.
     
  14. Rocky Mountain Priusman

    Rocky Mountain Priusman Active Member

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    Makes sense. I was just being a bit salty, but there are certainly shops that could do that in town here - thanks for your input.
     
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