Did Compression Test: Please analyze my results.

[Grandmaster]

EDIT: This is with a stock motor in my 93. No mods to the motor itself as far as i know.
Hey guys,
Well about 2 months ago i bought a compression tester from autozone and i've been putting it off and putting it off, so today (Christmas) i decided to stop being lazy and geterdone. Thats love right there, full compression test on Christmas day, with equal length headers

Here are the results:
#1: Quickly built up to 150, bro was watching the guage, said it took like 4 strokes then stayed around 150ish.
#2 Quickly built up to 145ish.
#3 same as number 2.
#4 3 strokes to 135, then onto 145 and stayed there.
#5 3 strokes to 125 then onto 145
#6 only climbed to about 125 over the seven strokes.
#7 the same
#8 Built quickly to 135 and hovered.

I dont know anything about what these numbers SHOULD be. Each cylinder was done with 7 strokes like the haynes manual said. Being Christmas, and being the pain it is to deal with the spark plug area with equal lengths, i didn't take the time to squirt oil in and recheck etc. ALSO: The haynes manual said to run the car to normal temp, which i did, before doing the test. But it took me so freaking long to get the plugs out and perform the test, by the time i got around to 5,6,7,8 the headers weren't even hot. Could this be why that side read low? Other than the motor not being at normal operating temperature, i cant think of anything i did wrong that might have altered the results. Are these numbers close to right? PLEASE analyze these the best you can and let me know what they mean and what i should do to fix them if they are wrong. THANKS!!!

 

[Grandmaster]

oh btw the car runs GREAT, doesn't smoke or anything like that, runs terrific, i was just doing this to check up like for future reference before i decide to boost it or something.

 

[JadeFalcon]

Not too bad at all, around 140 is great for that motor, has about 120k on the ticker?

 

[79'293stang]

sounds kind of low to me i had low compression dished pistons on my old engine and it made 170 plus or minus 10 all around

 

[90mustangGT]

I think your right, the number's gradually dropped as the engine got cooler for the most part. I would have only pulled one plug at a time and let it run a little between each cylinder test. Even though the results you got were off a little, they were all within the 25% mark of each other. 70psi is the minimum compression required to combust the fuel-air mixture. Those numbers are quite good, I wouldn't worry about your engine too much. I wouldn't bother adding oil to the cylinders because that is only nessasarry when you get bad compression. If you did and added oil and the numbers went up it would be an indication of bad rings vs. just a valve or head gasket problem.

 

[Grandmaster]

PHEW!!!
I cant thank you guys enough! <bows>
I would have only removed one at a time if i knew i could, the haynes manual said pull em all out lol. Doh, live and learn. Now that i know that i might recheck the 6,7,8 some time and make sure its at good temp, but not today or tomorrow, my arms hurt bad enough from scraping around as it is. Thanks a lot,
any more analysis is welcome.
-grand
EDIT: In reply to jadefalcon, i'm not sure how many miles. The odometer is in the 60s, but i've got 3.73s with a stock speedo gear and there's no telling how long its been like that. So yeah, 120k is possible, but there's no telling.

 

[Fox Saleen 163]

I would have only pulled one plug at a time and let it run a little between each cylinder test.

In order to do a proper compression check ALL plugs must be out of the engine. Also, the TB has to be wide open. I didn't know this either until I decided to read the directions that came with my compression gauge.

 

[TheUser]

yeah, might not want the motor to start while doing the compression test lol...mine said to remove all plugs too

 

[Fox Saleen 163]

Well, you're also supposed to remove the coil wire. So if it still starts after that, you car is possesed.]

 

[SR86]

Did the car have a block heater? The block heater side will have lower compression, due to the block heater restricting coolant slightly, and that side running a few degrees warmer, letting the pistons expand a little more, and over the years, that causes more wear.. Not a big deal, and most people dont' notice it, but my engine builder pointed it out to me..

 

[jerry beach]

I think your right, the number's gradually dropped as the engine got cooler for the most part. I would have only pulled one plug at a time and let it run a little between each cylinder test. Even though the results you got were off a little, they were all within the 25% mark of each other. 70psi is the minimum compression required to combust the fuel-air mixture. Those numbers are quite good, I wouldn't worry about your engine too much. I wouldn't bother adding oil to the cylinders because that is only nessasarry when you get bad compression. If you did and added oil and the numbers went up it would be an indication of bad rings vs. just a valve or head gasket problem.

I have always heard the spec is within 10% on all cylinders. I have pulled plugs one at a time and started the engine each time. Netted the same results and didnt hurt anything. Mine were 165-175psi at 105,000mi.

 

[Mavrick]

I have always heard/been told that aslong as your cylinders are around 20% within eachother, they are fine.