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Gen 2 used motor problems

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JohnStef, Nov 7, 2018.

  1. JohnStef

    JohnStef Member

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    I have a 2008 Prius that needs a donor motor. The 1st one I got from the salvage yard looked good over all but when I did a compression test one cylinder did not make more than 10 psi, the rest made 60 psi. So I got a replacement today. This one make 10 psi on only one cylinder, the rest are duds. I am cleaning the spark plug hole and putting 2 squirts of ATF in the cylinder to help seal the rings. I rock the motor back and forth and side to side to let the oil run around the full circumference - no luck. I am 0 for 2

    Am I missing something? Does an engine that has set for a year or more in the vehicle typically act this way? Or should I keep using the compression test to weed out bad motors?
     
  2. padroo

    padroo Senior Member

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  3. johnjohnchu

    johnjohnchu Active Member

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    It is well known that old gen 2 engines tend to burn oil, often substantially. Therefore, it probably will not be possible to find a good engine from junk yards in the U.S.. Perhaps you can source a very low mileage engine from Japan.
     
  4. 05PreeUs

    05PreeUs Senior Member

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    Um, burning oil has nothing what-so-ever to do with compression. Compression is compression, period.
     
  5. 05PreeUs

    05PreeUs Senior Member

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    A leak down test is the ONLY way to determine the condition of a non-running engine w/o a tear-down. Very likely BOTH engines are "good", you just cannot spin them fast enough to do a quality test. Most "compression tests" are done at cranking speed with a battery charger connected and the throttle plate WIDE OPEN. All are things which are impossible on a Prius. A leak-down test bypasses all of that and applies regulated air to the cylinder @ TDC (and often also @ BDC), measuring how much leaks out.
     
  6. edthefox5

    edthefox5 Senior Member

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    That’s not true. If your compression ring is worn your going to have a worn oil ring and you will blow by lots of
    Oil.
     
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  7. 05PreeUs

    05PreeUs Senior Member

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    Not necessarily. Most engines lose compression from overheating or ingesting dirt, neither of those typically affect the oil control rings as they are very low tension to begin with. Most oil consumption is from valve guides, poor quality oils can cause the oil rings to stick as another common malady, or a PVC system that is allowing too much air thru the system, which carries oil with it.

    You can have great compression with massive oil use and the converse as well. My point was, although not clearly made, just because you have low compression does not mean you automatically have high oil consumption.
     
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  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Am I the only one who is wondering how John is doing a compression test if the engine is not installed and therefore is not spinning at 300 RPM at minimum.
     
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  9. 05PreeUs

    05PreeUs Senior Member

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    Patrick, see my post, which is #5 above.

    You are spot-on tho, 200 RPM is considered the minimum to get a valid test.
     
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  10. T1 Terry

    T1 Terry Active Member

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    I think you will find the problem is small bit of carbon getting caught between the valve and seat. When you remove the spark plug you disturb small bit of carbon and they are causing the problem.
    I've been a motor mechanic for 45 yrs and I got caught by the same thing. Told the customer the compression was poor, removed the spark plug again to demonstrate to problem to the customer and there was full compression there this time. Rather red faced I asked around the trade if they had even had that and this was the answer. If it has been a long time since the engine has been run or the plugs have been out, you need to loosen the spark plug, then retighten them, start the engine and let it run for a while, then do the compression test.
    You could try compressed air into the spark plug hole while spinning the motor over and see it that will clear the carbon out of the valve seats.

    T1 Terry
     
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  11. JohnStef

    JohnStef Member

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    Thanks for the discussion above. My install is not yet complete but I have settled the question posted above by doing a simple leak down test. Thanks to all of the above posters for stating this.
    I went back to the salvage yard and told them my concern, that it failed my version of a compression test using a ratchet wrench to rotate the motor. The senior tech at the yard was patient with me and assured me that the cylinders did indeed hold pressure. He got an air line and hooked it up to his test hose, no sound, completely silent. I put my ear next to the oil filler opening, the exhaust output, no sound. All checked the same. With further assurances from him and his supervisor I took engine #2 home and am prepping it for installation. I know I should have used a leak down but there wasn't one there at the time.
    To see if the top end was good, I pulled the cam cover. The cam lobes look excellent, no abnormal wear and pretty clean. It had been setting a while so the entire inside had practically no oil. After prepping the cover and seal for reinstallation, I poured Mobil1 oil over both cams and down both sides of the timing chain.
    Does anyone have torque specs for the Valve cover bolts?
     

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  12. JohnStef

    JohnStef Member

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    Terry this was was my suspicion early on because on the 1st engine I could get 60 psi on 3 of the cylinders with a gage and hand cranking with a ratchet wrench. The salvage yard tests their motors by running them for more than 15 minutes before pulling for resale. So it was very likely a good motor, but my test method was bad.
    My test for future projects of this sort will be the Leak Down test.
     
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    89 in.-lb or 7.4 ft.-lb.
    80 in.-lb for the bolts that hold the spark igniters to the valve cover.

    You are supposed to use FIPG on the two places where the front cover, engine head and valve cover meet up.

    What is the odometer reading on the replacement engine?
     
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  14. JohnStef

    JohnStef Member

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    Thank you Patrick for the specs, the engine is sealed pretty well and the cam cover comes off nicely as the rubber gasket is not flat but kind of an upside down T shape, so I put grease on the mating surfaces and reassembled, and now torqued (correctly).

    112k, 2009
     
  15. JohnStef

    JohnStef Member

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    I got the engine in last night, I did 30 minutes worth of work in 2 hours - moving carefully
    This is just the placement, not power on - The install went way better than the removal.

    Taped doubled cardboard to the windshield edge so the exhaust manifold will not crack it.
    Removed the water pump
    Removed crank pulley
    Removed Intake manifold
    Removed 2 lower casting protrusions on passenger side of motor
     

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  16. JohnStef

    JohnStef Member

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    Power on.
    The salvage yard motor (112K miles, 2008) runs and works well. The test drive was successful, everything returned to normal. The hybrid system recharges while driving very well now.
     
  17. JohnStef

    JohnStef Member

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    P0420 showed up today. Cat is failing. This is actually helpful, I felt that the replacement engine is not very strong, mushy acceleration. Now a failed Cat could be the reason for poor performance. Easy fix
     

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  18. deces

    deces New Member

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    Congratulations!
     
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  19. 05PreeUs

    05PreeUs Senior Member

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    Doubtful, very much so.

    If a cat MELTS, it can block or restrict the exhaust flow, the photo you posted does not suggest any melting or other restriction. The sole job of the cat is to reduce emissions thru the process of "catalytic reduction", chemically altering/recombining combustion byproducts into less harmful ones. It is a chemical, not a mechanical process.

    The *most* likely cause of p0420 after engine work is an exhaust leak, followed closely by resetting of the adaptive strategies in the ECM.
     
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  20. JohnStef

    JohnStef Member

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    There were sand like particles in this chamber, I vacuumed them out as best I could, they were about the size of the white particles on the surface as shown in the photo. I figure these particles are jammed into the opening of each honeycomb. The photo shows aprx 20% blockage, this would not restrict flow enough to retard power?