How do i do a compression test?

[predator]

I want to do a compression test on my old crappy daily driver.. just to see how much life is left in it.

I've got a compression tester, but have no idea how to use it??

Do i just stick in one of the cylinders (remove spark plug and stick in) and start the car up??

Or do i just stick it in and it will it give me a reading while the engine is not running?

Anybody who has slightly more of a clue than me (not much) of how to do it, please let me know

[BHDave]

Stick it in a plug hole and disconnect the coils so she doesn't start, then crank it on the starter. Hopefully you have a gauge with a peak hold function. Don't know what it should read though

[sherlock_nzl]

Remove all spark plugs, I would also remove ignitor moduel plug to stop the sparks, hold throttle wide open, crank over 6 times, take reading, and do the same to all of them. pressure not that important as all gauges read different, most important is not having different pressures (eg, flatter battery lower pressure)

[wrxhoon]

sherlock is right , i hope u have long stem on your compression gauge to rech the plug holes .

the engine should be hot and crank at 300 rpm .

u dont say what engine it is but here is a guide.

rb20e 1.23 mpa ( limit .93)rb25de 1.26 ( limit .96)rb25det1.2( limit .90)and rb 26dett 1.18 (limit .88) variance limit .10 mpa

crank the engine until the pressure does't go up anymore ( usualy a few seconds ) then record the reading it may be in psi on your gauge. 1 mpa =138 psi apr.

if u r pressure is down on 1 or more put some oil in the cil crank it a little then check pressure again if it goes up to normal it means u have worn piston rings , broken rings or chipped piston in that cil. if it doesn't make any diff then its leaking valve .

i hope that helps u in someway and as sherlock said dont wory if u r readings are low , maybe slow cranking speed or the gauge .

as long as they are all the same its good .

if they are all the same then put a little oil in the cil and try again if the reding is the same again its all good ( its unlikly that all valves are leaking the same amount .

[predator]

Thanks for the very useful info.. this is actually for an old car (1987 XF Falcon..4.1L ), which has no such fancy thing as coil packs and things. The info provided will be useful for checking the compression though in that one. I have a factory workshop manual so I guess I can find the correct factory figures.

May also try on my RB25DET Skyline also.. i *think* the stalk is long enough but I know what you mean.