I just bought my first Prius, a 2006 with package #7. I would like to check the compression ratio on the ICE and wondering what the procedures are or if anybody has done one. Any help would be appreciated.
The procedure for checking the compression requires the Toyota Scan Tool so that you can put the Prius into "Inspection Mode" and then choose the menu item: DIAGNOSIS / ENHANCED OBD II / HV ECU / ACTIVE TEST / CRANKING RQST. I believe it is possible to put the Prius in Inspection Mode without the scan tool, but I don't think it is possible to command the Cranking Rqst without the scan tool. If you have access to a Leakdown tester, you might be able to run a Leakdown test instead of a Compression test. I believe you could do the leakdown test without any proprietary scan tool, but I haven't tried (and haven't had a reason to).
Thanks for the advice. By the time you responded, I had already done the test. I probably didn't do it correctly because all I did was remove all of the sparkplugs and hook up the compression gauge up to one cylinder at a time, turned the engine over and recorded the reading. I got 135-150 psi over all cylinders. That is lower than the 13.5 compression ratio, but I was more concerned about the consistency from one cylinder to the others. I don't think I did any harm to the engine because I'm getting 45 mpg after the test and the engine sounds and feels normal. Any comments?
Because of the Atkinson cycle that is used (after induction about 1/3 of the inlet charge is pushed back out again) the compression ratio is effectively about 9:1. kevin
The pressure you saw is about right for the above effective compression ratio. Note that the engine is spun faster than in a "normal" car. No, you wouldn't do any damage to the car doing the test the way you did. Nice bypass of all the computer systems! You -could- get the computer all upset doing what you did as the expected engine start didn't occur, but I guess if you shut it off after a few seconds (the time it takes for a compression reading) it doesn't enter a code.
I'm sure you didn't do any harm. However I don't know what to make of your pressure readings, since a normal engine will be spinning at ~300 rpm via the starter motor while the Prius engine was probably spinning at 1K+ rpm via MG1. You are right that the main concern is that the readings should be relatively constant.
You said, "turned the engine over...", but didn't say how. It seems everyone else understood what you meant but me - guess I'm kinda' slow. Did you just go to READY mode and wait for engine to try starting then shut it down as soon as it started to crank?
