300zx z32 93 compression test

[nathanmoris]

Hi i was wonderin what the heck is going on here..

I did a compression check and did what the book told me to do..Disconnect spark plugs and remove alldisconnect fuel pump relay and remove pressurewhen testing press pedal to open throttle body and off you go..

when doing this i get..passanger side.. 200psi, 215psi, 190psiDSrive side.. 190psi, 210psi, 180psi

the book says nor is 186 and can only be off by 14 between cyclinders..I have white smoke coming out of my tail pipe so i pretty sure that i need a new head gasket thats whats everyone telling me... but i was trying to see which one if not both but i dont get these readings... am i doing something wrong thanks for the help...

[evildky]

when doing a compression test it's better to wire the throttle open so you have a consistant opening, as for the readings, the standard reading is 186 psi, and the minimum reading is 142 psi, with a max difference os 14 psi, now, what brabd is your tester? how accurate is it? if you have a cheap one or maybe just an old one thats maybe been dropped a few times, lets assume it's just a bit off, we'll assume your highest reading is 186 and each other reading is39 psi lower that your readings, that would put your lowest at 141, which is of course just below the minimum, so it's safe to say you have a problem f some sort, you might even want to get ahold of a new gauge to verify before you tear into it

you can give each low reading cylinder a squirt of standard engine oil and reteat to see it the redings improce, if the readings improve you have scarred cylinder walls and or bad rings, either way you need a rebuild, if there si no improvement then you have a head, or headgasket problem, eaither way the heads gotta come off, it's always a good idea to have a machine shop give them a onceover, to be sure they're not warped, esprecailly if you've gotten it hot

further more, typically when a HG goes, you get lots of white smoke, a littel at start up can be normal, especially when it's cold out, but huge clouds of white smoke mean your burning coolant and need a HG, and sometimes you'll find your oil gets milky as can leak coolant into the oil, this can damage your bearsing and kill your engine quickly

and just to be extra sure, have you recently done anything to the car like a timing belt? getting a tooth off can give you some wierd readings as well

[nathanmoris]

hi thanks for the help..

i have tried to different compression gauge and get the same thing... ill try putting some oil in the cyclinder to see if i get a differnet reading... and as for any jobs that i recently did only injector replacements.... Do i need to remove both heads or do i only need to do the one with the low compression and it is smoking alot so its coolant burning thanks for the help jon

[tg]

if you're in there anyways, you'd might as well change both since the other is probably not far behind.

There are alot of common parts that need to come off to service the head, so for the little extra work, and a cheap head gasket, you'd be best to do them both and have a look at your cylinders while you're at it.

[evildky]

yeah if you gotta pull one it's cheap insurance to do both, be sure to have a machine shop give them a once over, you can address any leaking valves, or valve seals in addition to mating surface