Compression test on Toyota hybrid
Good morning every body, I have a case study to discuss the proper way to do a compression test. I work for a shop where we service hybrid vehicles, however, this is the first time I am performing a compression test on this type of vehicle. The customer requested this because the vehicle needs a HV battery pack and he wanted to know the health of the vehicle (ICE).
I checked the specification and it is 118 psi max with a 14 psi difference (I would like to know the spec from experienced guys about what percentage you use to rule out a compression issue that will cause a misfire relative to slight low compression) between cylinders. The engine is warm and my compression results are 150 psi. The customer asked what the specification is, and what the actual formula is to determine a worn-out engine. You'll see the results below.
I would like your opinion on the test that was done with a Snap-On scanner and Toyota Tech Stream. Same peak compression archived at 150 psi.
*Edited by Diagnostic Network Staff 11/9/18
118 psi is not the maximum pressure, it is the standard pressure. More is fine as long as all 4 cylinders are the same. Technically all spark plugs should be removed and the throttle held at WOT white testing.
The Prius Atkinson expansion cycle engine uses VVT-i to increase the cylinder compression ratio while cranking to aid in quick starts (especially in cold weather). It also uses VVT-i to decrease cylinder compression when stopping the engine to reduce the bump on shut off. The compression appears to be great.
From Toyota TIS:
Standard compression pressure:
813 kPa (8.3 kgf/cm 2 , 118 psi) or more
617 kPa (6.3 kgf/cm 2 , 89.5 psi)
Pressure difference between each cylinder:
100 kPa (1.0 kgf/cm 2 , 14.5 psi) or less
yes , I understand about the atikson cycle and the scanner is commanding the trans axle mg1 in this case to do rpm like normal engine that has started motor and also is disabling injectors and coils also is commanding the vtc to set at certain point during the test .
is that information from TIS you got there??
because all data has specif as you can see there 3 ranges , compression and it does not mention 118 psi or more , also 2 minimums pressure and 3 differences that was my confusion. But as you mentioned as long as they are even in relation to each other . thanks for taking the time
I agree with John, higher compression is fine as long as they are all even. As far a giving the vehicle a clean bill of health: The gen3 (09-15) Prius is know for head gasket issues. I've seen them present as misfires, coolant consumption and even external leaks. When they misfire it can cause a loud knocking noise in the transmission that could lead you to believe there's a transmission issue but it's really just a misfire. Hope this helps.
Hi Joel I would like to see your results when you remove the one way valve from the compression gauge and test the running compression , rather than the peak compression. The engine is being run at ‘idle speed ‘ Rather than conventional cranking speed so this to me would be more relevant
Remember you running compression will vary from time time on this engine / atikcon cycle when first you start ups this vehicle cranking cold the ecm wanted to see minimum 5 grams per second on the maf or they give you a code , engine fail to start , you can monitor this data pid from cold to warm and your grams per second will vary , they are doing some thing with the throttle , vetch and so on , since the in cylinder pressure transducer measure difference in pressure I do not have idea if will give you definite unswere abouth (ICE)running health .
also (ICE) internal combustion engine .running you will create a misfire and this engine with misfire you heard like the transaxle is going to break apart, fluctuation in rpm.
John Kelly's comments on the specs is spot on. TIS has more detail.
It is important to separate tests. The active test in the HV ECU is the one for intrusive testing with a gauge. The Active Test in the Engine ECU is the relative test and is read by looking at the "speed of cyl #X" PIDS and the " AV engine speed of All Cyl" PID. The speed of cyl pids are only valid with the active test operating. The 51199 value is the default data place holder. When the test is activated, there is a delay until the data updates. That is the point in time where the data is read. When the test is turned off the default of 51199 returns. That is exactly what the Snap on scanner is showing. If you used that rotational speed for the relative compression test but used a gauge it would explain the higher compression. There is a hint in TIS that reads...... "at first, the techstream display will show each cylinder's engine speed measurement to be extremely high. After the engine started, each cylinder's engine speed measurement will change to the actual engine speed."
For what it is worth, a plug not properly tightened will show a gain of about 20 RPM over the others in the relative test routine indicating the lower compression. Single digit variations in engine speed from these tests are normal results. Even a 4.0L with 280K miles on the clock can still show a 4 RPM spread. The average speed PID will be slightly higher than the individual cyls.