Did a compression test on my 88 Celica

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Results turned out better than I expected. The engine was fully warmed, then shut off for close to an hour. From left to right, I got 202, 185, 205, 208. I wonder why number 2 would be as low as it is? All 4 spark plugs looked clean with no unusual wear, except for some oil on the threads of the plug from the first cylinder. I plan on replacing them with a set of NGK v-power plugs when I get a chance. I was going to change my oil today too, but I couldn't get it up on my wheel ramps because the plastic bumper lip thing would catch on the ramps before the car was fully up on the ramps.
 
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quote:
Originally posted by 55: Results turned out better than I expected. The engine was fully warmed, then shut off for close to an hour. From left to right, I got 202, 185, 205, 208. I wonder why number 2 would be as low as it is? All 4 spark plugs looked clean with no unusual wear, except for some oil on the threads of the plug from the first cylinder. I plan on replacing them with a set of NGK v-power plugs when I get a chance. I was going to change my oil today too, but I couldn't get it up on my wheel ramps because the plastic bumper lip thing would catch on the ramps before the car was fully up on the ramps.
My guess is you have some carbon buildup in your combustion chambers. Unless you're running 10:1 or better compression ratio, 200+ psi sounds high.
 
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That looks pretty good. I don't have a manual for your car so I don't know what its compression is supposed to be, but I suspect #2 is a little low rather than #1, #3, and #4 are all high by almost precisly the same amount. However, it's still within ~10%, so that's not terrible. I wonder if folks here would suggest trying Auto-rx thinking that the rings on #2 are a little carboned up and a cleaning would even the compression out? I've never used Auto-rx.
 

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Originally posted by bulwnkl: I wonder if folks here would suggest trying Auto-rx thinking that the rings on #2 are a little carboned up and a cleaning would even the compression out? I've never used Auto-rx.
That was exactly what I was thinking, if only shipping costs weren't so high. I'm hoping that when I fill the oilpan with GC, and with some 'spirited' driving, it might break up some of the carbon that could be sticking the ring pack, and giving such a high compression reading. I believe the 3S-FE engine had a compression rating of 9.5:1, or something around that.
 
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I don't believe sticking rings will cause higher compression. It is carbon buildup within the combustion chamber- on the piston and head decreasing the chamber volume- which will cause higher compression. If it were carbon in the rings, such as sticking rings, then they wouldn't seal and you'd have poor compression. In one of my carb books I thought I remember reading that cylinder pressure had to be below 200 psi for typical gasoline engines (assuming 93 octane) otherwise it's too high and would preignite. If anything your 185psi cylinder is probably close, the others have some buildup. Would be cool if you could pull the head and verify. In any case, a dose of seafoam or other top end cleaner is in order, and not necessarily autorx in the oil cause that won't clean carbon out of the combustion chamber. I also remember reading here, molakule or Patman I think posted, of using a Lube control mix as a soak to dissolve carbon that worked pretty well?
 

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Yes, I remember reading something along the lines of either an LC or a Seafoam piston soak. I'd like to give that a try.
 
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I would remove the plugs from the engine cold. I would then add 2 onces to each cylinder. Then put a 19mm socket onthe crank bolt and turn the engine over by hand a few time. Let it sit over night. Crank by hand again then reinstall plugs. Fire the beat up and watch the white smoke fly out the exhaust! I would then add the 16 once flush dosage of LC to the oil and run for 15 minutes! Then drain out the old oil. Add fresh oil and 4 onces of LC. Then from here on out add 2 onces every 1000 miles! Now if you like you go the Auto-Rx route as well it surely will not hurt!
 
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