300z engine compression test one cylinder very low - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

*brett* · 08-03-2016, 08:17 PM

#1 cylinder 110 psi
#2 cylinder 160 psi
#3 cylinder 180 psi
#4 cylinder 160 psi
#5 cylinder 180 psi
#6 cylinder 150 psi

I just bought the car it has 194k miles on it. im actually surprised with the pretty good PSI on most cylinders. the engine was apart when i bought it so i never was able to start it. the previous owner said there was an engine knock. im assuming valve tapping since i see thats common with these. would that be a reason cylinder 1 is so low?

wabogabo · 08-13-2016, 01:37 PM

It could be a couple of things, valves might leaking for low compression on cylinder #1. also it might have overheated but the gasket is still holding up somehow which highly doubt it. To determine if the engine has a rod knock, try to rotate the motor by hand from the crankshaft bolt to see if turns 360 degrees. If your having trouble rotating the motor it can be rod knock or seized up.

Good Luck

kruked · 08-15-2016, 11:32 AM

Doesn't matter. You have more than 15/20 psi difference between all cylinders. Strip it naked and rebuild it.

Juan[email protected] · 08-15-2016, 12:28 PM

Quote:

Originally Posted by kruked

Doesn't matter. You have more than 15/20 psi difference between all cylinders. Strip it naked and rebuild it.

not necessarily,

was the compression test done cold or warm? had the car been driving prior to this or sitting for a while? it could be a number of things. did pouring a small cap of engine oil in the cylinder make the compression numbers go up or not?

I've seen JDM motors give compression numbers that were all over the place. (90-155 differences) after install and getting driven on / cleared out of the deposits report back with solid numbers. so if you can give us some history on the car and the exact conditions in which you did the compression test we can give you a better answer as to what you can do to properly diagnose your situation.

wabogabo · 08-15-2016, 01:20 PM

Quote:

Originally Posted by [email protected]

not necessarily,

was the compression test done cold or warm? had the car been driving prior to this or sitting for a while? it could be a number of things. did pouring a small cap of engine oil in the cylinder make the compression numbers go up or not?

I've seen JDM motors give compression numbers that were all over the place. (90-155 differences) after install and getting driven on / cleared out of the deposits report back with solid numbers. so if you can give us some history on the car and the exact conditions in which you did the compression test we can give you a better answer as to what you can do to properly diagnose your situation.

Yeah also you can do a wet compression by putting oil in the spark plug holes, if compression goes up that means the rings are starting to go bad

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08-03-2016, 08:17 PM	#1
brett Leaky Injector Join Date: Feb 2011 Location: Howell, NJ Age: 32 Posts: 105 Trader Rating: (6) Feedback Score: 6 reviews	300z engine compression test one cylinder very low #1 cylinder 110 psi #2 cylinder 160 psi #3 cylinder 180 psi #4 cylinder 160 psi #5 cylinder 180 psi #6 cylinder 150 psi I just bought the car it has 194k miles on it. im actually surprised with the pretty good PSI on most cylinders. the engine was apart when i bought it so i never was able to start it. the previous owner said there was an engine knock. im assuming valve tapping since i see thats common with these. would that be a reason cylinder 1 is so low?

08-13-2016, 01:37 PM	#2
wabogabo Join Date: Jul 2011 Location: San Diego, CA Age: 31 Posts: 46 Trader Rating: (0) Feedback Score: 0 reviews	It could be a couple of things, valves might leaking for low compression on cylinder #1. also it might have overheated but the gasket is still holding up somehow which highly doubt it. To determine if the engine has a rod knock, try to rotate the motor by hand from the crankshaft bolt to see if turns 360 degrees. If your having trouble rotating the motor it can be rod knock or seized up. Good Luck

08-15-2016, 11:32 AM	#3
kruked Nissanaholic! Join Date: Feb 2012 Location: someone's sisters' pants Posts: 2,288 Trader Rating: (37) Feedback Score: 37 reviews	Doesn't matter. You have more than 15/20 psi difference between all cylinders. Strip it naked and rebuild it. __________________ I like my bikes how I like my b¡tches...naked! 2014 Triumph Street Triple