I had my 03 Cobra sold until a compression test was done. The passenger side was 145-150. The drivers first two cylinders were inthe 135 range the third was 90 and the last was 60. I have no mods done to the motor. The car has 49k miles and sits for long periods of time. I try to start it when I remember. I took it to the Ford dealer. I was told that on the low cylinder the leak down was 50%and I need a new motor. The car runs strong and does not smoke or overheat. The check engine light is not on. The only thing I have noticed is that sometimes it cranks over a lot before it starts and sometimes when the cooling fan comes on the RPM drops like the car wants to die. I had the car smogged in September and changed the oil and filter.The aboved mentioned spinning and stalling were not noticed. Help?

 

was the motor cold when you did the test? if so that'll mess up the numbers since the oil isn't really making a seal with the rings. try idling the motor up to normal temps and then run the test again. also make sure that you're flooring it during the test, leaving the throttle body closed will give low numbers. it's also fun to scare your buddies by doing that, mean, but funny

on my old hondas their manual says once there's a 20psi variance between pistons then it's time for a rebuild. a 50% difference is huge and the motor should feel pretty weak compared to new at that point.

 

Just a suggestion.

You are in the 2005-2011 section of the forum.
You might get more help if you were in the 96-04 year section of the forums.