compression test results

[fiveOcalypsO]

ok, i am going to try to explain this in as much detail as i can. i have a 1993 lx 5 liter mustang with 133,000 miles on it. i gave it a compression test this weekend and the highest number was 140 and my lowest was 130 with other numbers varying in between. i know this is ok because that is well within 25% i mean it's even inside of 10%. i did the testing on a warm engine and by taking every spark plug out one at a time and replacing it with the tester, i have since learned that i should have taken them all out. I know that there are lots of variables but i want to know if anyone can give me a rough estimate on how much of a difference i could get in my numbers if i would have taken all of the spark plugs out. oh and my battery wasn't fully charged either, i have a lot of problems with it, and i read that this can be a factor for compression test numbers as well. any ideas or information would help me out

 

[7upstang91]

I'm not really sure. I thought that you were supposed to take them out one at a time. sorry.

 

[fiveOcalypsO]

ok well i guess i really don't care i just thought that 130-140 seemed kind of low, and i've been reading on here that most people don't care as long as they're within that certain percent, but i would like to know what a kind of compression numbers a brand new 5 liter would give so i can kind of compare it to mine. i do have a lot of miles, but i would just like to see where i'm at and what i should be worrying about.

 

[Wallzy]

I would say that your fine; not one cyl is conciderably low. I am under the impression that you have the stock camshaft in the car - which if you didn't may be another reason...but sometimes the cam timing or lifters may have an effect on cyl psi. For instance if your timing chain was lose/stretched over 133,000 miles the cam timing would be off - this would cause the cam to be retarded compared to where it is intended to be opened and closed. Another possibility is that your lifters are not remaining pumped up when the car is being turned over due to being worn. This can change the duration seen on the valve, reducing overlap but changing when IV & EV are opened and closed - ultimatly can effect the cyl psi. Hope that this helps,

Walz

 

[7upstang91]

I have heard that you want to be 130-150. You are right there I wouldn't worry at all.

 

[fiveOcalypsO]

thanks guys