Ok after my compression test I seem to have low numbers. Trying to figure out if I have head gasket grief. Took each plug out, started it and tested numbers. All are between 50 and 90 pounds. Seems awful low to me. What should the numbers be? 1998 F-150 with 4.2l engine.

 

Minimum 100 psi and only 15% difference between cylinders. Normally a reading of 150 is not unheard of. Me thinks you have a worn out engine.

You do a compression test by pulling ALL plugs out and hold the throttle wide open, NOT with the engine running, disable the fuel and/or ignition system.

 

If those numbers are correct how the hell does it even make it out of the driveway. What kind of issues are you having, how many miles on the motor, what is your maintenance been telling you? Put up some pictures of what your spark plugs look like.

 

Ok. I will get some pictures up. Apparently I am not doing the test right. I will do it again the way explained above and see what those numbers are. Thanks gang!

 

#1. 100+ pounds
#2. 40 psi
#3 40 psi
#4 > 100 psi
#5 > 100 psi
#6 > 100 psi
The passenger side rear of engine has really low compression.

 

Blown head gasket or cracked head.


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