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so i desided to do a compression test on my 4.6L in my auto class and i got some puzzling results. presuming cylinder #1 is on the passenger side, cylinders 1-4 showed and average compression of 145 psi, normal. so i start testing the drivers side, thats when it gets weird, the cylinders would work there way up to 145 psi, but when i stopped cranking the psi would drop to zero. my car has never had a misfire problem ever. i even tried another tester with the same results.my instructor said it may be a blown head gasket. so any thoughts.
 

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We need to know the pressures on each cylinder, not just an average before we can provide any help.

And IMHO screw a compression test. Do a leak down test on each cylinder and find out what is really going on. Compression test are mainly to see if you have a cylinder that is completely dead.

I highly doubt you have a blow head gasket since the car is running fine. And even if it is, your pressures would be low on two adjacent cylinders, not a whole bank.

My WAG: The pressure release mechanism on the test set(s) is(are) leaking.

But just my opinion. :thumbsup:
 

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^^^ What he said..

On my compression gauges there is a small schrader valve almost like the ones in tire valve stems. Either the schrader valve is stuck open or the pressure release is stuck open like 94DD was saying. Once upon a time, my valve got stuck open. Since then I have been replacing the valves with tire ones and they will work for doing a few cars and then get stuck open again. Good luck and I hope you figure this out. It is very strange that two compression gauges would give you these problems, but if you were reusing the "adapter hose" that screws into the head, thats where the schrader valve is.
-Rob
 

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It's from the fuel the injecter were spraying it washed the rings down u have a dumb teacher hate to say it but 4.6 do not blow headgaskets I've seen them lift under boost but never cause any problems, so do not worry about the proper way would have been to kill the fuel pump

Robert
 

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well my teacher worked on fleet police vehicles so he does know what he's talking about.
That doesn't answer whether or not you or he killed the fuel during the test. I've done work on the local police vehicles too, yet I'm not about to claim that I know what I'm talking about just because of that.
 
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