5.0 engine compression test - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 7 Old 05-20-2019, 06:25 AM Thread Starter
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5.0 engine compression test

blew a intake gasket, and did a compression test.... average was about 100psi per cylinder... any thoughts?

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post #2 of 7 Old 05-20-2019, 06:57 AM
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Leak down test next

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post #3 of 7 Old 05-20-2019, 07:54 PM
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compression test is a relative test


you compare all holes

as said, leak down will give you a better idea of sealing power

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #4 of 7 Old 05-20-2019, 08:05 PM
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Those numbers are low.Is it a high mileage motor?? If its leaking coolant into the oil,repair the intake gasket asap before driving.I had an Edelbrock RPM that was leaking for a few weeks and eventhough I done an oil change 2 or 3 times in those few weeks,thats all it took to eat my bearings down to copper.The dreaded rod knock and 0psi oil pressure at operating temp at idle,began in that 2 to 3 week period too. Unfortunately it was my only vehicle at the time so I didn't have a way to just park it until repairs could be done.BTW - I was working 16 hours a day 7 days a week,so I literally had 0 time to replace the gasket.So don't let it slide.During the compression test,did you have the throttle body plate fully open,was the engine at operating temp and did you do a wet test afterwards??

Short story: I was on vacation in PC Beach Fl years ago and my lx began to run like **** on the way home.It burnt 1.75 tanks of fuel from Tn there and almost 4 tanks on the way home.Done a compression test and 7 cyl had 165psi,but 1 had 90psi.One of the valvespring locks had popped out,but even with something as bad as that being wrong,it still had 90psi,so I would definitely do a leakdown test to see if the rings are suspect or possibly the valves/valvetrain.
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post #5 of 7 Old 05-20-2019, 09:52 PM
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low compression on all holes may indicate something, may be the throttle wasn't open

wouldn't put too much into compression numbers, unless there is a spec it should be, but i am sure its not stock

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #6 of 7 Old 05-21-2019, 06:22 PM
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Leak down tester are for checking the barrel valves on Top Fuel cars.
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post #7 of 7 Old 05-22-2019, 03:45 PM
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Quote:
Originally Posted by Mark O'Neal View Post
Leak down tester are for checking the barrel valves on Top Fuel cars.
man that thing is a life saver.. tuneup and everything was right on when i followed the setup advice i got from alkydiggers... car runs like a champ now...
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