These compression numbers ok ?? -
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > These compression numbers ok ??

Zone Offroad Body and Suspension Lift Kits, Brackets, DiscJeep Wrangler Framless, Bowless, Trektops 92-95 YJ, 97-06 Baseline 4x4 Lifetime Warranty 4340 Chromoly Axle Shaft Ki

Unread 07-17-2011, 01:20 AM   #1
Registered User
1998 ZJ 
Join Date: Aug 2010
Location: Virginia
Posts: 4,525
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

2013 6.2 V8 Camaro SS 9k miles
1998 5.9 V8 ZJ 180k miles
1998 4.0 I6 Laredo ZJ 227k miles
Candymancan is offline   Reply With Quote Quick reply to this message
Unread 07-17-2011, 04:45 AM   #2
Registered User
1995 ZJ 
Join Date: Jan 2011
Location: Alexandria, Virginia
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.
TheHalfWit is offline   Reply With Quote Quick reply to this message
Unread 07-17-2011, 02:53 PM   #3
Registered User
1995 ZJ 
Join Date: Dec 2010
Location: Norman, OK
Posts: 2,307
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.
jnicewan is offline   Reply With Quote Quick reply to this message

Quick Reply

Register Now

In order to be able to post messages on the forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools

Suggested Threads

Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. is not in any way associated with Jeep or the Chrysler Corp.