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How do you check the engine compression on a Gen 3 Prius?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Robert Holt, Apr 7, 2015.

  1. Robert Holt

    Robert Holt Senior Member

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    With vehicle engines in the past, I have used a compression check as a fundamental part of routinely checking the wear on an ICE. My usual method was disconnecting the ignition, removing spark plugs, inserting the compression gauge line in a spark plug hole, and turning over the engine with the starter. How exactly do I do that sequence with a Gen 3 Prius?

    If that method is not feasible, would a "leak down" method of checking compression such as we did on old aircraft engines possibly work with the Prius ICE? To do that I would have to be able to carefully position the crankshaft so that the intake and exhaust valves were fully closed on each cylinder in turn. What is the safe method to do that with the Prius ICE?

    Does anyone know exactly what the compression reading should be? I am assuming that if the engine is spun at 1000 rpm by MG1, the correct reading would be 13 to 1 or 13.5 to 1. Or?

    Particularly if I start having oil consumption, I want to be able to rule out ring and piston wear as a possible cause so that I can concentrate on the other likely culprits. And if I were purchasing a used high mileage Prius, the compression check would be a fundamental piece of information on the engine's health.
     
  2. bisco

    bisco cookie crumbler

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    i think there's a way to spin the ice for testing, but don't know what it is.
     
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  3. Robert Holt

    Robert Holt Senior Member

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    Maybe the "maintenance mode" trick?
     
  4. bisco

    bisco cookie crumbler

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    it could be. i'm sure there's a thread or post buried in here somewhere.
     
  5. fuzzy1

    fuzzy1 Senior Member

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    Don't forget that this engine is an Atkinson cycle, the intake valve closes quite late. The correct reading should be much less.
     
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  6. bisco

    bisco cookie crumbler

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    you may want to download the service manual. 15 bucks a day or something?
     
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  7. Robert Holt

    Robert Holt Senior Member

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    Ack! You're right of course! I was thinking of the exhaust expansion ratio and the compression check at idle would be the intake compression ratio which would be the normal 10 to 1 or so. Not used to Atkinson cycle engines yet.
     
  8. ChapmanF

    ChapmanF Senior Member

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    With a laptop running Toyota's Techstream software plugged into the diagnostic port, you have a command that tells the engine to crank at 250 rpm for your compression-testing pleasure. The acceptable range of pressure readings can be found in the service manual at techinfo.toyota.com.

    If that's not convenient, your leakdown test idea is a perfectly good one. That's a nice test because you've got less cranking noise and you can really hear if you've got hissing into the exhaust or intake manifolds, bubbles in the coolant, etc.

    There doesn't seem to be a single standard size for the orifice in a leakdown tester, so it's difficult to give figures to compare between people using different makes/models of tester. On the other hand, it doesn't depend on whether the engine is Atkinson or Otto cycle, so whatever numbers are considered good in the literature with your leakdown tool ought to be good.

    -Chap
     
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  9. Mendel Leisk

    Mendel Leisk Book Cover Judge

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    You're in for a world of hurt just getting a spark plug out: Google "youtube nutzaboutbolts spark plug". About an hour's disassembly, the wiper arms, motor and bottom of windshield cowl all have to come out.
     
  10. css28

    css28 Senior Member

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    Per alldatadiy (to which I subscribe) compression test pressure is 118 psi (813 kPa), min pressure is 89.5 psi (617 kPa) and difference between cylinders should be no more than 14.5 psi.
     
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  11. Mendel Leisk

    Mendel Leisk Book Cover Judge

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    Compression test is about 2/3 of way through this. Didn't really read it; Techstream is mentioned, and to have the car in maintenance mode.
     
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  12. ChapmanF

    ChapmanF Senior Member

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    I can't help noticing those 'alldatadiy' numbers are all different from the ones in Mendel's attachments (which I trust are from the service manual on techinfo.toyota.com).

    That's one of the reasons I don't go anywhere for my service info except the Toyota manuals....

    I forgot to answer that part earlier. It's a really low friction engine, so the answer is
    1. make sure the system is OFF so nothing will try to start the ICE
    2. put hand on crank pulley
    3. turn until timing mark points where you want it. :)
    The tricky bit is holding the crank in that position when you put the air pressure on. I just used a breaker bar and socket on the crank pulley nut, wedged the handle against the ground with my foot while standing up to open the air valve and note the readings. It worked, if the contortions were a little awkward.

    -Chap
     
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  13. Mendel Leisk

    Mendel Leisk Book Cover Judge

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    Mine are from a single pdf, file titled "Repair Manual". Could be some supersceding going on. This is page one:


    Capture.JPG
     
  14. Robert Holt

    Robert Holt Senior Member

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    Thank you, gentlemen.
    (Have to say that electrical wiring diagram manual also looks like fascinating reading!)
     
  15. ChapmanF

    ChapmanF Senior Member

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    Toyota's wiring manuals are super. You don't just get circuits, but the routing of all harnesses, locations of all junctions and ground points, a whole section dedicated to identifying any connector by location, color, and shape (and with part numbers in case you need to replace one) ... anybody doing electrical work or diagnosis and trying to do without is playing a big self-imposed handicap.

    The "New Car Features Manual" might have a forgettable title, but it's a hugely useful manual. All the other volumes tell you how to diagnose what's wrong with stuff or fix it, but they are filled with assumptions that you know what all the stuff is in the first place and why it's there and how it's supposed to work. That's all what's in the New Car Features Manual.

    -Chap
     
  16. css28

    css28 Senior Member

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    I have to agree. Big difference between 118 psi and 199 psi.
     
  17. Options man

    Options man Junior Member

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    That’s an easy one
     
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  18. ianmacduck

    ianmacduck New Member

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    Thank you, Chap. I imagine that the 5,179 KB wiring manual file that goes along with the 179,547 KB repair manual that I bought from Rock Auto is not the one to which you are referring. I am guessing that your manual is the online TIS one? I was very disappointed in my purchase, which had no index, and no harness/component illustrations/locations. Looks like I will have to drop $20 every time I want to troubleshoot some electrical on my 2010. Let me know if I am mistaken, please :) Thanks for the info.
     
  19. ChapmanF

    ChapmanF Senior Member

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    Sometimes people will sign in to TIS once, or a few times, and do a lot of download/print-to-file to be able to refer to stuff later when they might not be online or paid up.

    Sometimes people also share the files they downloaded (which, to be clear, you agree not to do when you sign in to TIS). There's a big PDF you might be able to find online with most of the 2010 repair manual. There's sort of no rhyme or reason to the parts it's missing—just whatever sections the folks doing the downloading forgot to download—most of the hybrid-system DTC detailed descriptions are missing, and the whole airbag section is the one from the previous generation. Go figure. But enough of it is there to be helpful for a lot of jobs.
     
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