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Engine Diagnosis

232 Views 3 Replies 3 Participants Last post by  BB98GLS
Hello i have a 2004 Regal LS it has the N/A 3800 Series 2 L36, the last owner abused it

I was going up a Pennsylvania mountain when the trans burnt up on me.
swapped a new one in, started it up and i got smoke blowing out the tailpipe, i pull the engine got it on a stand
and i do a compression test.

Compression test showed all cylinders ranging 55-70 PSI
did a wet compression test and got identical results.

did a Leak down test and realized i suck at it, the measurements didnt help but i had the pistons at the top position and heard hissing coming from both the dipstick and intake throttle body. i only tested cyl 2 4 6 with same results

ive had no mechanic experience before this and learned a lot but this has me stumped and praying the thing isnt toast.
if anyone has information or any advice anything is appreciated.
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Not sure why you went thru the headache of pulling it for compression test, but it may have a couple blown head gaskets, if there was a heat issue from not being maintained up to snuff before that mountain driving. Also might've bent valves if you over-revved it real bad, which isn't a super difficult operation, either.

It'd be about $100-200 in gaskets/bolts/fluids to get them off, clean it up, check that they're flat, and reassemble. Gives a chance to make sure you het the aluminum AC Delco lower intake gaskets. Go slow and look up notes on assembly (new head bolts... torque specs/patterns for heads/intake... Teflon for lower intake bolts, RTV at corners of valley, etc.)
I can help you with the Leak Down Test. I have done over 500 leak down test in my shop over 30 years. What seem to be the problem? A Leak Down Test is one of the best test to see how well combustion chamber area holds cylinder pressure. You are using air pressure at Top Dead Center during this test. I set the pressure for 100 Psi. Make sure you have a big enough air compressor to supply constant air flow for the test. I would say, that it is about better test than a compression test because you have it on the engine stand. YES, it best to have the engine hot operating temperature between 180 - 210 degrees to make the test accurate. This is vital for both compression and leak down test.
Since the engine is out of the car your best choice is the Leak Down Test. Make sure the oil cap is on when proceeding the test. SINCE the engine is on the stand, remove upper intake manifold and both exhaust manifolds. This will eliminate all air leak mistakes and simplify the procedure. Make sure the block is filled with water/ coolant to the opening of water outlets / intake thermostat housing. During the test, it will help you with leaking head gaskets by having air bubble coolant outlets or head gasket areas.
Take your time, make sure the cylinder you are working on is at top dead center ( TDC ). Air is going to always leak out of the dip stick tube ( blow by the piston rings ). REMEMBER the engine is cold. Air leaking out of Intake port could mean a bent or bad valve valve or seat. Same deal can happen to the exhaust side ( exhaust port ).
Leak Down Tester that I use has two gauges. One measure air line working pressure and the other cylinder air pressure. Their are many types in the industry and I don't know what you are working with. Their is many YouTube videos on Leak Down Test procedures. Watch a bunch of them and don't get discouraged. TAKE YOUR TIME in doing this test. It may save you a lot of money and you will know what wrong with the engine!

Best of Luck !! Bernie 😎
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This time around do ALL the cylinders! Just remember if you are not at top dead center with the piston, the air pressure will push the piston down. 100 psi of line air pressure with 100 psi reading gauges is a no brainer to use. On a cold Leak Down Test you want no more than 30 % leakage on a cylinder test....
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