If any of you have been following my other post, you know that my TPI engine is running rich. I was told to do a compression test
https://www.thirdgen.org/forum/Forum1/HTML/028419.html

Well, most of the cylinders were at 195, and highest was 210 and the lowest was 180. So basically they were spread from 180-210.

Someone said the readings were gonna be like 110. Why is mine so high? This good or bad news?

Thanks


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1989 IROC
305 TPI/A4

-just trying to keep it running

 

They are supposed to be within 10% of each other. The 210 and 180 is a little more than that, but its close. 110? Thats way too low. Just about any car should read 150 or more. I have a car that reads in the 190 range, so there is nothing unusual about the readings you got.

Sounds ok to me. Check the low one again just to see, you can try putting some oil in there and see if it comes up, but I wouldnt worry about it.

 

They look good to me.

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ASE Mechanic/Machinist/Smog Tech

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GO #3

 

thanks, so the bottom end is in relatively good shape?

 

compression test doesn't tell you anything about the bottom end. another test to get a better understanding of your cylinders,
valves and related parts would be to do a leak down test.

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ICON Motorsports

 

well can I atleast assume that the pistons are in good shape?

 

EDE is correct, a leak-down test is a more accurate method for checking the sealing ability of the rings (you'll need a compressor and leak-down guage), although I do not agree with his statement "...compression test doesn't tell you anything about the bottom end...". I believe that it does give an indication of the rings/valves, it's just not as accurate as a leak-down test. If I am wrong, please explain.

If QUICK's figures of 180-210 PSI are correct, I think that that would indicate the rings are sealing okay (although it is slightly outside the 10% range - you may want to recheck the lowest cylinder).

FYI, altitude will affect your readings from a compression check (not the leak-down method). I believe the factory gives the specification at sea level, but the reading will be less (I think it's 3% less per 1000 feet above sea level, but am not sure) at higher altitudes. 195 PSI at 4000 feet would equate to 23.4 PSI difference to the PSI at sea level (the air is denser at sea level) at the 3%/1000feet rate. The important thing is that each cylinder is within 10% of eachother. The difference in PSI at different altitudes is important only when you are comparing PSI figures to a specification (normally given for sea level).


[This message has been edited by Stuart Moss (edited July 29, 2000).]

 

I agree with madmax & engineboy, for a high-mileage engine those don't look too bad.

Several things besides the actual seal of the valves and rings affect them: the amount of carbon build-up in each cylinder; whether you had the throttle blocked wide open; and most importantly, the condition of the cam. A cylinder with a lobe worn more than another, or that holds less oil after the oil pressure goes away, will read higher than others while one with a lifter that holds more oil will read lower. If you have 2 adjacent cylinders that both read lower, it's head gasket time.

You may also find, if you have a bad injector or 2, that those cylinders will have more carbon buildup in them, and will read higher. An injector is cheap; you might want to get one and swap it into each cylinder and see if it makes a difference.

I can't see how anything to do with compression would make fuel injection run rich. I'd be looking at things like FPR, O2 sensor (I'd start there actually), and injectors. If you're not losing oil then your rings are pretty much OK.

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"So many Mustangs, so little time..."

 

Thanks to everyone who replied.

I feel a little better now knowing that those numbers are good enough

Thanks again
Jeff

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1989 IROC
305 TPI/A4

-just trying to keep it running