Autonerdz forums

This vehicle lacks power on acceleration. The compression on starting is 90psi.
#1-could the valve timing be manipulated to deliberately cause low compression during starting?
#2-what method would the manufacturer use to do this & why?
Toyota has no compression specifications in their service information that I could find but Motor specification is minimum of 155psi.

This is a reman engine, not Jasper, with 5000 miles. Did a running compression on a Toyota Prius with 1.5L that looks identical but has a different engine number that has the same compression. Customer states that this has been a problem since install & thought it was normal.

This is the first time I've use the autonerdz forum so I'm kind of feeling my way around.  The question remains could this be a normal condition?  I matched it to a Prius running compression waveform and it was identical in where the evo was.  It looks to me like the evo is about 12 degrees before bdc.  Also the snap throttle appears to be about right.  Thanks for the response.

All four cylinders identical and the ignition seems to be occurring at the right place and the 200 psi at snap throttle appears to be in line with Motor specs.

No codes, vehicle came in for an oil change and the customer mentioned it seemed low on power but attributed that to being a new engine.  I drove it, seems fairly normal in first and second gear but wont get out of it's own way after that.  I can get cam and crank with ignition but that's be Monday.  There is no sensor on the exh cam.  The question is could it simply be normal?  The marks are in alignment but the intake cam is rotated farther than the exhaust at top dead center.  Thanks for the reply.

Hi Mike,

Welcome to the forum. Not sure if this is a strategy issue or not. If you think the PCM is controlling the phaser operation and advancing the intake phaser. I would disconnect the solenoid to keep oil pressure out of the phaser and retest and see what your results are.

Looking up specs for this engine I see the max compression is to be 213 psi and the low of 156 psi. In the markup I did you are at 92 psi. Your running compression at closed throttle I can except of  90 psi. The WOT is at 200 psi. This is possibly a lil low. For a three cylinder engine I would think the compression may be a little higher on the snap

Now as other have suggested. Do a cmp, crk. primary and WPS. Set the scope up to 500 ms/div at 6 ms sample rate and take a few frames for us.

Also, Rich mentioned scan data. Good idea. Post up the snappy data for us as well.

Also, read the thread on the forum here about doing a breathing test. Derreck did a heck of a job on his class presentation. You will find this in the Group therapy part of the forum. Very useful info there.

If you have question navigating the site just ask.

Here is a couple markups I did based on the info provided.

KarlW wrote on Jul 5^th, 2015 at 3:42am:


The cranking speed had me questioning it as well Karl. It is one of the reasons I wanted an ignition event.

Not sure but it may be an Atkinson cycle engine which may explain deep exhaust expansion, but then it doesn't explain low compression

Who's our Toyota experts here?

https://en.m.wikipedia.org/wiki/Four-stroke_engine