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How to do a compression test.

Keegzzz

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Possible head gasket leak or blown, just need to know exactly how to do a compression test and what p.s.i and kpa I'll be looking for in a 98 vt.
 

IRON8

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170, i think.. remove all spark plugs, screw in the compression reader? keep the throttle wide open through the whole process, turn key and crank it 5-6 times... you should reading about 170 but mainly you just look for a level reading from all cylinders
 

Brett_jjj

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The ecotec minimum compression reading should not be less than 690 kPa (100psi). And the lowest reading on any cylinder should not be less than 30% of the highest reading on any cylinder. You really need a workshop manual for a VT. The manual says,
Engine at operating temperature.
Remove spark plugs (obviously).
Remove fuse number F25 from the engine compartment relay housing.
Fit the gauge to number 1 plug hole.
Crank the engine over at least seven compression strokes, and watch the gauge. The compression should build up quickly in a healthy engine. Low compression on the first stroke followed by gradual increasing pressure on the following strokes indicates worn piston rings. Low comnpression on the first stroke, which doesnt build up on successive strokes indicates leaking valves or head gaskets or cracked head etc. Record the highest reading obtained.
Repeat on remaining cylinders. On cylinders that read low, add a teaspoon of clean engine oil to the cylinder through the plug hole, and then retest, if the compresion now reads normal, the rings/bores/pistons are worn.
 
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Jxfwsf

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or another quick easy test


i would highly advise making sure the radiator cap is off before connecting the air line, ignore him saying being low on coolant is ok, probably is for that engine but in the newer engines there should be no air in the cooling system at all..
 
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Brett_jjj

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Id say its the main EFI power fuse, im pretty sure they would say to remove it so the EFI doesnt fire the injectors as the engine is cranked over.
 
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