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Thread: Compression Test: PSI differences?

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Posts: 1-10 of 16
2008-05-03 15:22:29
#1
Compression Test: PSI differences?
After doing a compression test these are the numbers that came up. And I'm wondering why there is such a difference between them all.

When doing this.. I warmed up the car, Pulled the fuel pump fuse, let the car run to stall, pulled the 1st plug out, hooked up the gauge, held gas pedal down, turned the crank until gauge didn't raise anymore.

From there left the 1st spark plug out and went down the line. When I got to #4 all other 3 plugs were out. And in #4 is where I got the highest PSI..

Any idea why? Here are the pics.. You can see the differences.

155-165-160-170







2008-05-03 15:41:09
#2
Aren't you supposed to pull all of the plugs and then test the compression so there is little resistance from the other cylinders?
2008-05-03 15:49:37
#3
sr20de motor?
2008-05-03 15:52:39
#4
Standard is 185 psi with a min. of 156.
2008-05-03 16:01:47
#5
Originally Posted by silvia1320
Aren't you supposed to pull all of the plugs and then test the compression so there is little resistance from the other cylinders?


This I didn't know..

Originally Posted by GT2871RBLUBIRD
sr20de motor?


Yes

Originally Posted by 91grayDET
Standard is 185 psi with a min. of 156.


So then it's with in specs? But why such different numbers?
2008-05-03 16:23:34
#6
Yeah it's the spark plugs. Pull them all out and I bet you'll get pretty even numbers across the board.
2008-05-03 19:21:43
#7
Just thought I'd post this since it's still handy from the other thread haha. Even if you got those differences with all the plugs out they still fall in the FSM difference specs (well 1 Psi off but):

2008-05-03 19:56:48
#8
So then I'm good no matter what the numbers are as long as they fall in the 185-156 range?
2008-05-03 19:59:14
#9
Originally Posted by Sentrixx
So then I'm good no matter what the numbers are as long as they fall in the 185-156 range?


As long as they are 156-185psi and no more than 14psi different from each other.
2008-05-03 20:05:52
#10
It would be barely out of spec, which wouldn't really be great. I'm confident, however, it would test much better with all of the plugs out.
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