compression test numbers

[truker]

hello everyone: I'm doing a compression test on my 98 mounty 5.0 and I need to know where the numbers should be for a good or bad reading? Thanx Truker

 

[koda2000]

i would say around 160 pounds and each cylinder s/b with 10% of the others. don't forget to have the t/b open during the testing. if a low cyl comes up with a squirt of 30 weight oil = bad rings, if no dif = bad valves.

 

[Maniak]

hello everyone: I'm doing a compression test on my 98 mounty 5.0 and I need to know where the numbers should be for a good or bad reading? Thanx Truker

From what I have found in my searching of EF, the "minimum" # is 100psi

The big question is, are they even?.. If you have 1 or 2 cylinders that are lower than the rest, that is much worse than all of your cylinders being low-ish..

Part of the issue with looking for a "normal" compression # is it is dependent on atmospheric pressure. If your at sea level your going to get higher #'s than if your at 3500 ft

~Mark

 

[koda2000]

From what I have found in my searching of EF, the "minimum" # is 100psi

The big question is, are they even?.. If you have 1 or 2 cylinders that are lower than the rest, that is much worse than all of your cylinders being low-ish..

Part of the issue with looking for a "normal" compression # is it is dependent on atmospheric pressure. If your at sea level your going to get higher #'s than if your at 3500 ft

~Mark

Florida is about as close to sea level as you're gonna get...

 

[Maniak]

Florida is about as close to sea level as you're gonna get...

True...

Was just pointing out "normal" numbers for 1 person can be different than another..

I ran into that when I was checking vacuum on the 460. I was chasing low vacuum until one day when I was talking with Lunati and they asked my elevation. I was missing 3+ inches of vacuum because I was > 3500 ft in elevation.

~Mark

 

[truker]

Thank you Koda, should I pull the fuse on the fuel pump or disconnect the coil pack? I'll send you a message with the results in one or two days, by the way I can't figure out what the abbreviation: t/b means?

 

[Maniak]

Thank you Koda, should I pull the fuse on the fuel pump or disconnect the coil pack? I'll send you a message with the results in one or two days, by the way I can't figure out what the abbreviation: t/b means?

t/b is throttle body.. put a brick on the gas pedal when you do the test so the throttle plate is open.

~Mark

 

[koda2000]

t/b is throttle body.. put a brick on the gas pedal when you do the test so the throttle plate is open.

~Mark

yes, remove the fuel pump fuse or relay first. note: less than 160 lbs isn't necessarily bad, it's more important that the readings be close to one-another (w/10%).

you need to have the throttle body (t/b) open so air can be pulled into the engine easily to get good compression readings. i guess a brick on the gas pedal will do the job.