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compression test????

Hi i have a 1989 mustang gt with a 302 it has 104,000mi on the engine and i was wondering what the compression is supposed to be... thanks, steve

Re: compression test????

Please read the Sticky at the very top of the Blue Oval Lounge.

Moved to the Windsor Power Forum.

Re: compression test????

About 125 to 135 psi cold after about 10 cranks with the TB open.

Re: compression test????

120 is OK. But what is the variance between cylinders. That is more important. 10-15 % is about all you should have.

Re: compression test????

???? how do you tell

Re: compression test????

Measure each cylinder. The high and low readings are what you compare.

Re: compression test????

Remember that this test should be performed with ALL of the spark plugs removed from the heads and the ignition coil primary harness disconnected (I usually stick a small light bulb into the socket to act as a load for the ignition module). It may also be advisable to pull the fuel pump fuse so that your cylinders aren't getting drenched in gasoline. :eek: Also, remember that after performing this test "dry," you might want to add two tablespoons of motor oil to each cylinder, right before taking another compression reading. If the pressure raises dramatically, it means that your rings are worn.

I second Gearhead's notion that the balance between the cylinders is what is important. Typically more than 10% variance, and it's time for a rebuild. Perhaps you should purchase a service manual for your vehicle, as most of this information is contained therein.

FWIW, 120psi seems awfully damn low. Are you sure your gasket on the gauge's hose is sealing properly, and that you're opening the throttle fully?

Re: compression test????

When I did my compression test on my 200,000 mile 5.0 I didn't know about opening the TB, or cranking the motor ten times, I only did it about 2-3times with TB closed, but i did remember to unplug the fuel pump, and I still got an average reading of 125psi, all I can say is God bless Mobil 1.