These compression numbers ok ?? -
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post #1 of 3 Old 07-17-2011, 01:20 AM Thread Starter
Web Wheeler
1998 ZJ 
Join Date: Aug 2010
Location: Virginia
Posts: 5,548
These compression numbers ok ??

Ok i did compression test, as i've never done it b4 on my 5.9 and these were my results. With a warm motor i tested it dry and then squirted oil in there.

#1. 160, with oil 167

#2. 150, with oil 155

#3. 164, with oil 167

#4. 165, with oil 168

#5. 163, with oil 169

#6. 163, with oil 168

#7. 164, with oil 166

#8. 160, with oil 165

Is this ok ? Number 2 seems low, but it didnt Jump anymore then the others did with oil in it. I checked it twice to make sure. I dunno number 2 has me a little worried because its like 10-15psi lower then the others.

Btw i disconnected the ignition oil, and move the wires away from the coil itself. I didnt have the engine on WOT tho.. read that after i did this.. Is this ok ?

One thing i noticed was when reading #2 which is the one closest to the ignition coil the engine was sputtering and shaking and the light in the engine bay was flashing.. I have no idea why it did that on #2 and not the rest. Could it be because the coil is closest to #2 ? Should i try it again and maybe remove the coil from the engine all together, cause it acted like it was actually trying to start

Candymancan is offline  
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post #2 of 3 Old 07-17-2011, 04:45 AM
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1995 ZJ 
Join Date: Jan 2011
Location: Alexandria
Posts: 695
Its within the acceptable range, what I did though was yank the fuel pump relay since that's much simpler. All you need to do is prevent it from starting. WOT should prevent it from starting since its gas pedal is connected to the throttle body, but unless you have an assistant you might not be able to crank it and watch the gauge while holding the throttle open.

Acceptable range is usually 10%, so that isn't outside of the specs.

Calm. C.

If a week goes by without needing to replace something, pinch me because I must be dreaming.
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post #3 of 3 Old 07-17-2011, 02:53 PM
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1995 ZJ 
Join Date: Dec 2010
Location: Norman
Posts: 2,348
Those numbers look good to me, I personnally like to see no more than 10% difference as mentioned above, but even 20% would be considered ok. The reason for cranking at WOT is to allow as much potential air into the cylinders as possible. Cranking at WOT also disables the fuel injectors via PCM, it is a "clear flood" strategy. I usually just unplug the coil just so ign sparks dont fly around.
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