Compression Issues
10-10-2009, 08:02 PM
#1
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Compression Issues So as I was testing the problems on the truck, I drove it down the street with the lack of power problem being way worse now and heard a few backfires, but they werent that loud. So out of curiosity I ran another compression test after pulling a few plugs to check to see how it was running. They are white as always, so I do another compression test and find that half the cylinders on both banks have low compression. The gauge bounces up and down between 65 and 75 and when you cut the engine off the gauge holds steady at about 84. I am guessing this would probably mean valves right? I did pull the valve covers again and oil is coming up, rods look fine, and so do the springs. Doubt it is the lifters too. And just an assumption, if I was losing compression due to rings, I would have a steady low compression reading correct?
10-10-2009, 08:58 PM
#5
You can find the trouble without the leak down tester..just pull all the spark plugs and find a way to attach a air hose from a air compressor with about 75 psi air. With the piston at tdc listen for air leaks in the intake , crankcase and exhaust.
10-10-2009, 09:16 PM
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I thought about that but I would have to get a regulator anyway rather than just throw air into the cylinders and I would have a gauge to watch too.
Stupid question too, but does the damper have a mark on it or do I have to pull the valve covers and check the rockers for setting TDC on each cylinder?
Stupid question too, but does the damper have a mark on it or do I have to pull the valve covers and check the rockers for setting TDC on each cylinder?
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10-10-2009, 10:02 PM
#8
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The LS1 factory-style balancers do not have timing marks, the crankshafts do not have a keyway for the balancers like SBC/BBC have, so the blancers just go on in any position. The LS1 firing order is 1-8-7-2-6-5-4-3 according to the Haynes Repair Manual.
10-11-2009, 06:51 AM
#10
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remove #1 plug and insert a rubber tube or something relatively soft but large enough to stop the piston. Turn the crank clockwise till it stops (this is easier with all the plugs out) and mark the dampner with a pencil. Now turn the crank counterclockwise until it stops and mark that position. The midpoint between your two marks is TDC cyl #1. Mark that with a pemanent marker or paint as TDC. Now turn the crank clockwise 1/4 turn and mark each 1/4 turn as 2, 3, 4. This way you will have TDC for each set of pistons through the firing order.
10-11-2009, 11:04 AM
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remove #1 plug and insert a rubber tube or something relatively soft but large enough to stop the piston. Turn the crank clockwise till it stops (this is easier with all the plugs out) and mark the dampner with a pencil. Now turn the crank counterclockwise until it stops and mark that position. The midpoint between your two marks is TDC cyl #1. Mark that with a pemanent marker or paint as TDC. Now turn the crank clockwise 1/4 turn and mark each 1/4 turn as 2, 3, 4. This way you will have TDC for each set of pistons through the firing order.