Well how nice!

G

gixxer750

2jzget comingsoon!
Mar 30, 2005
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I was changing my plugs today, and I decided to do a compression test, since I haven't in about 5000 miles.

Well, I start at the back, TB open, turn over 3 cranks. Number 6 is at 165. 5 is at 164, 4 is at 166, 3 is 165.... Then I get to cylinder 2. 90 PSI on cylinder 2. It came up to 85 on the first rotation, and went to 90 on the second. The third rotation of the engine it didn't change. Hmmm...

I go ahead and do number 1 and get 166. So then I go back and do number 2 again. I crank it over about 10-15 times. It is Still exactly 90. That is kind of strange I think, so I add a tablespoon of oil. It only comes up to 106.

Does this sound like a ring problem, or maybe something else. I'm going to borrow a leakdown tester this week and check that. I'm thinking maybe a valve clearance is off or something. Adding oil should have done more that that I would think. I mean, it only changed 16 psi, and in the past when I have done oil on cylinders in cars it changes the readings 40-50 psi....


Thoughts on this?
 
Nick M

Nick M

Black Rifles Matter
Sep 9, 2005
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Adding oil only changes cylinder pressure if you have a sealing problem in the cylinder itself.

There may be nothing wrong with it. You could have a spark plug hole that is slightly damaged. If you confirm that it is 90 psi, you should have felt it driving. If you didnt, you are getting a false reading for some reason.
 
aljordan

aljordan

LEADED FUEL ONLY
Jul 14, 2005
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Nick M said:
Adding oil only changes cylinder pressure if you have a sealing problem in the cylinder itself.

There may be nothing wrong with it. You could have a spark plug hole that is slightly damaged. If you confirm that it is 90 psi, you should have felt it driving. If you didnt, you are getting a false reading for some reason.
Click to expand...


FWIW.. I have 2 cylidners low on compression. 2 and 5 or something like that. POint being, they aren't next to one another.

Anyway... If I didn't do a compression test on this motor, no way would I have known it had a problem. Runs absolutley flawless otherwise. THese weak cylinders are at 100 and 120. The others are 145-147.
 
D

Doward

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Jan 11, 2006
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It's in the valve :) Probably a worn guide, or a valve that isn't sealing correctly. I'd do a leak down test, to be certain :)
 
N

NDBoost

Guest
so what is the proper way to do a compression test?

When i did mine i just left all plugs in and went through each cylinder 1 by one replacing the spark plug each time i moved to the next cylinder. I left the Throttle alone etc im assuming it wasnt right..
 
G

gixxer750

2jzget comingsoon!
Mar 30, 2005
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Mississippi
this was also a fairly cold compression test. Car had been sitting for two hours or so.. It takes time to clean the oil out of the center spark plug valley ;)

I've noticed this engine has a miss cold that goes away when warm. I may pull number 2 plug when it is at operating temp, and see what I get.

The engine pulls strong, and put down 341 whp last dyno.... It runs fine once warm, but always has the miss when cold. It is not burning any oil, the plugs were all beautiful(autolite 3923s) after 5000 miles. I'm pretty sure its not the HG, as I am getting no white smoke, no coolant loss, no water in the oil. If I rev the piss out of it from under the hood, I don't even get any blowby from the PCV system... It has to be a valve issue. I'm wondering if I need to check my clearances.
 
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