General Technical & Electrical General technical and electrical discussion for the Ford Ranger that does not fit in any other sub-forum.

Compression Ratio

Old 05-06-2014
Thread Starter
Join Date: Jan 2011
Location: Easthampton, Ma
Posts: 17
Compression Ratio

Can any one tell me what the correct cylinder compression should be on a 1999 Ranger 3.0
Old 05-06-2014
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Join Date: Jan 2014
Location: Vancouver, BC
Posts: 12,507
No, because there isn't one...................

A compression test has too many "tester" variables for the manufacturer or anyone else to put out a specific number.
Engine temp
battery charge(starter motor speed)
intake open or closed
all spark plugs removed(changes starter speed)

On any vehicle with a gas engine you should expect 150 to 180psi

But the point of a compression test is to test all cylinders at the same time, so variables are all the same, and then compare the numbers, they should all be within 10% of each other.

Higher compression is not always good, could be carbon build up.
Lower compression 120psi and down is never good.

3.0l has a 9.3:1 ratio, this is about the top for using regular gasoline, 87 octane, 3.0l like the 2.3l(9.2:1 and 9.4:1) would start pinging if fuel mix or EGR system was not perfect.

All that being said a new 3.0l should show about 175psi with perfect test parameters

Last edited by RonD; 05-06-2014 at 10:00 PM.
Old 05-07-2014
Thread Starter
Join Date: Jan 2011
Location: Easthampton, Ma
Posts: 17
Thank you Ron. I'm getting ready to do the test and wanted to know what to look for.
I'm all set.
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