whats the correct way to do a compression test? do you crank it only five times or crank it until the pressure doesn't go up anymore? what is considered a full crank?


i would think you would crank it until the pressure doesn't go up anymore to get the full psi, but then i heard you only crank it 5 times...so whats the correct way to do it? i get a better reading if i crank it until the pressure doesn't go up anymore.

 

You want to crank it until the gauge stops going up.

Keep in mind that you never want to be on the starter for more than 6-8 seconds at a time, and you want to let it cool down a little too.

 

thanks

 

Usually 10 cranks, 720 degree rotation of the crank will provide the maximum psi per cylinder. Make sure you do the test on a cold engine, you get much lower readings when the engine is warm or full temp.

 

 

why do you get lower readings when you're engine is cold?

 

I've seen the opposite, I've seen warm engines give higher readings, presumably because of piston expansion and oil on the rings.

Also, I have found that personally it takes only 6 cranks or so to get full pressure, not 10.

Your mileage may vary though, of course.

 

what is consider a full crank?

 

"rrrrrRRRmmm"

Just go out and turn the key until the damned gauge stops going up. You're making this way too difficult.

 

One big thing that I just learned over the weekend is that you need to have the car at WOT while cranking it over. For so long I was only getting like 150psi in all 4 and I thought that was pretty low with 9.2:1 pistons then I read in the Acura service manual that it needs to be at WOT did that and pressure rose to like 185psi

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 30psi Teg &raquo;</TD></TR><TR><TD CLASS="quote">One big thing that I just learned over the weekend is that you need to have the car at WOT while cranking it over. For so long I was only getting like 150psi in all 4 and I thought that was pretty low with 9.2:1 pistons then I read in the Acura service manual that it needs to be at WOT did that and pressure rose to like 185psi</TD></TR></TABLE>

exactly, WOT and the engine needs to be warmed up all the way. why would u want to compression test a motor cold....do u drive your car with your motor cold?(other then the first 5 minutes of course )

it needs to be warmed up for full piston/ring expansion, even on N/A applications

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote"> Make sure you do the test on a cold engine, you get much lower readings when the engine is warm or full temp.</TD></TR></TABLE>

Err.. huh?? I always got better numbers on a fully warmed block than on a cold one..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">. Make sure you do the test on a cold engine, you get much lower readings when the engine is warm or full temp.</TD></TR></TABLE>

I didnt even see this... NO. the engine must be warm to ensure proper ring and cylinder expansionand besides that small cracks when the motor is cold open up when it is warmed. I had a blown headgasket and cold the compression test was fine but hot and I was way off.

 

geez guys, leave boosted hybrid alone. Im sure it was a typo He could school 90 percent of this board.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by intekragsr &raquo;</TD></TR><TR><TD CLASS="quote">geez guys, leave boosted hybrid alone. Im sure it was a typo He could school 90 percent of this board. </TD></TR></TABLE>

lol thats soo tru....im sure it was a mistake...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by intekragsr &raquo;</TD></TR><TR><TD CLASS="quote">geez guys, leave boosted hybrid alone. Im sure it was a typo He could school 90 percent of this board. </TD></TR></TABLE>

Chill out, nobody was mean to him or anything. Someone has to correct the error, or it's going to be wrong whenever someone digs this post up in the archives.

If he has a problem, he can bring it up with whoever. Until then, stop trying to police us.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kpt4321 &raquo;</TD></TR><TR><TD CLASS="quote">

Chill out, nobody was mean to him or anything. Someone has to correct the error, or it's going to be wrong whenever someone digs this post up in the archives.

If he has a problem, he can bring it up with whoever. Until then, stop trying to police us.
</TD></TR></TABLE>

Im not trying to police anyone. Seems like your taking the job. Its obvious you cant see past the sarcasm, or the " " I inserted.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kpt4321 &raquo;</TD></TR><TR><TD CLASS="quote">
If he has a problem, he can bring it up with whoever. Until then, stop trying to police us.
</TD></TR></TABLE>

C'mon, its not that big of a deal..no one is "policing" here....

 

I do both "cold" and "hot" compresion test. Why? Because you can spot particular problems by performing both test.

Best method is to disconnect the distributor harness, block the throttle open and then test the cylinders in firing order. I also never crank more than 10 times.