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Trouble with tdc on cylinder #1.

J

jaxx83

New member
3800 series III engine non supercharged 2004 grand prix gt2. messing around with compression and leakage test of my engine. felt compression stroke on cylinder #1 by putting finger in cylinder #1 spark plug hole untill pressure was ported out/blowing on finger. turned crankshaft twice (one camshaft revolution) and verified i was on the compression stroke. i then ported 100 psi very slowly into the cylinder and turned the crankshaft manually farther into the current stroke / progression of strokes until the crankshaft / crankshaft pulley did not turn under the full 100 psi that i ported into the cylinder. now, i could not move the crankshaft / pulley either way from that spot without the pressure forcing the piston down. Have i achieved TDC of cylinder #1? Furthermore cylinder #1 & #3 failed compression test. #5 passed. however for all the lh cylinders (1-3-5) air was pissing out the intake at the point i described? Havent even tried rh cylinders. #5 tested good, i am doing something wrong.

(cant do pencil tricks, etc. even using a piston stop with graduations would be difficult as i cant even see the spark plug hole)(dont as far as i could tell make an actual piston stop peg tool/timing peg that is set for that specific engine. this is what i have used before)

HELP / SUGGESTION WOULD BE APPRECIATED...........
.....ABOUT TO SLAP IT BACK TOGETHER AND SAY FORGET ABOUT IT.
 


Why are you doing a compression test in the first place? What's going on with your car? To do a compression test I'm pretty sure you put the gauge on and crank the engine over and see what the gauge tells you.
 
high oil consumption per gm manual. car under warranty for a bit longer. diagnosis not covered. diagnosis estimate 800 bucks from non-gm local/small eng shop. performing leakage test also while spark plugs are removed.need to find tdc of cylinder #1. worked on recips in school we had a tdc peg. you find compression stroke, turn eng till piston hits tdc peg that was screwed into sparkplug hole and bam tdc of first cylinder in firing order. use degree wheel from there to get tdc of all pistons. dont make em for gm from what i found. they make generics, some people make their own. but only a true peg made for that engine is dead on. since gm doesnt make em, since the dealer was like wtf when i asked on the phone (that would be parts clerk and service tech) there must be another way. several online forums, etc. say about markings but i have seen none. have actual gm manufacturers maint. manuals to perform tasks. nothing stated about timing or how to achieve tdc with timing markings. only need to find tdc of cylinder #1 for sure. If the action i described in the 1st post (which im new so is under introduction cause i got no clue about this site yet) above is correct, obviously i have a problem. i am working on the vehicle to try and narrow down/diagnose myself as i cant afford pricy diagnosis or an iffy shot in the dark repair. boredom/learning plays a role as well.
 
to do a compression test don't you just screw the gauge on and crank the engine over and that gives you your compression? If you hear hissing into the intake try tapping on the valve springs and see if they seal up.
 
Basically. Must crank certain amount of times. Must get certain values on all cylinders and then with all cylinders in comparison to eachother. Leakage test requires porting air to the cylinder with piston at tdc and measuring the leakdown rate. It is at this point you can tell if your exhaust valve, intake valve, head gasket, and piston conditions depending on where the air is pissing out. Normal condition is no air. Both valves are closed on tdc and piston rings should have minimal if no blow by.
 


I believe it's standard for a dealer to diagnose and fix a problem under warranty. Especially if the work is deemed warranty work based on the diagnosis.

Anyone seperate shop that is suggesting a price of $800 to diagnose oil consumption is clearly buying you a large drum of lube before bending you over. This diagnosis shouldn't take anyone more than an hour of time.
 


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