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Compression Check?

99prixgt

99prixgt

club of used to own a gp
Today I was fiddling around trying to get a reading for compression. This is my first time doing this. I have a very simple needle gauge that connects into the spark plug hole. I was cranking the motor by hand for a while (big pita) and the most the gauge read was below 30psi. I then tried the next cylinder and it did the same thing. Am i not using the gauge correctly? How is this done? Would the reading be off if there isn't a t/b and some vacumme lines are un-done?
 


for reference my gauge looks like this

CompressionGauge.jpg
 
you dont crank the engine by hand, you unplug the ignition module, cuts spark and fuel and you crank it for about 5 sec. that hose has a schrader valve correct? you will need one so it holds the reading for you
 
minichopper6hp said:
you dont crank the engine by hand, you unplug the ignition module, cuts spark and fuel and you crank it for about 5 sec. that hose has a schrader valve correct? you will need one so it holds the reading for you
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Yes it does have that schrader vavle. Someone told me to crank it by hand :o. Ill try cranking it, would it matter if i don't have a throttle body and some vacumme lines are un-done?
 
why would you crank it from the inside of the car? that would turn the motor over and you wouldnt get a solid peak reading...
 
Bio248 said:
why would you crank it from the inside of the car? that would turn the motor over and you wouldnt get a solid peak reading...
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what?! thats how you do a compression check. it has the schrader valve there to hold the max reading.
whoever told you to crank it by hand is wacked out
 


i have DONE it by hand. mine doesnt have a valve on it so i HAVE to do it by hand and hold it at TDC to get the reading.
 
i have done it by hand and by the starter and the results where night and day. the readings that i took on the starter where much higher than the ones done by hand. my gauge also does not have a valve on it but the gauge it self saves the highest reading then i need to push a button to release the pressure. One of the times i spun it by hand i was only seeing 30psi and it turned out the timing was off. i had the crank key way at 3oclock and not 2 oclock on the RM timing set
 
I was seeing below 30psi and i didn't touch the timing, only thing was i removed the harmonic balancer and it ran fine before i took the motor apart. Did i do the compression check wrong?
 
try spinning it with the starter and see what you get for pressure then. now where you getting below 30 on all cylinders or just 1??
 
you guys think im dumb but the proper way to do a compression check is with the starter. I dont pay $30k to go to a well known automotive school to get false information
 


Im with minichopper6hp
we used a remote starter hook up when we checked compression and let it go for about four to five "puffs" with the ignition disabled And fuel pump relay fuse pulled
We had 3 clesses where comperession tests were taught.
And thats from 3 college instructors with over 80 combined years exp
 
like i said. i HAD to do it by hand because of the gauge i was using. no one says you guys were wrong, that is just the only way i knew how to do it.
 
You will never get an accurate reading doing a compression check by hand. I have never heard of such a thing.
 
gixer2000 said:
try spinning it with the starter and see what you get for pressure then. now where you getting below 30 on all cylinders or just 1??
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I started with the #5 cylinder when it read below 30, then i moved to the #3 cylinder and got basically the same thing, then i stopped because i figured i wasn't getting anywhere, I didn't crank as many times on #3 because I thought i was doing it wrong.
 


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