Compression Test Result. Bad or Good ?

[The_one]

Hello Guys,
I am back with the compression test result. I did the compression test today (7/24/2006) @ 8:30pm with both the dry and wet (add oil). I followed the same procedures mentioned at the VFAQ website.

Results (From Left to Right):


Dry: 133-135psi, 130psi, 130psi, 130psi
Wet: 140psi, 140psi, 140psi, 140psi

I don't know the 10psi variation is bad or good? Your inputs are welcome.

* I am approximately 5,000ft above sea level (Denver)

Edit: Changed title. -oldman

 

[2gGSX]

The good news is that all your numbers are close to each other. The bad news is they're low. The extra 10 psi is not significant enough to indicate ring failure from what I've seen on other cars, but you do have a very tired engine. A leakdown test will give you more information.

 

[diablos991]

Though it is true that you don't have ring falure, they are definitely worn.

What prompted you to perform a compression test?

 

[The_one]

The good news is that all your numbers are close to each other. The bad news is they're low. The extra 10 psi is not significant enough to indicate ring failure from what I've seen on other cars, but you do have a very tired engine. A leakdown test will give you more information.[/QUOT

From your experience, what do you think are the possible factors that cause my engine to output such a low psi ?

 

[The_one]

Though it is true that you don't have ring falure, they are definitely worn.

What prompted you to perform a compression test?

Here is my story
http://www.dsmtuners.com/forums/showthread.php?t=234655

 

[garrett21]

A question i had about doing a compression test is should the engine be hot? warm? or cold? If any one KNOWS a exact answer please let me know. Thanks.

 

[diablos991]

The engine should be at normal operatin tempurature. If it isn't your numbers will be inaccurate.

 

[The_one]

A question i had about doing a compression test is should the engine be hot? warm? or cold? If any one KNOWS a exact answer please let me know. Thanks.

I did my compression test when the engine was warm. Better charge your battery before you perform the test

 

[diablos991]

Well based on your previous story, I would recommend a boost leak test. Have you performed one yet at 20psi?

 

[The_one]

Well based on your previous story, I would recommend a boost leak test. Have you performed one yet at 20psi?

Tomorrow I will do the boost leak test at 15-18psi. What do you think that cause my engine to have low psi result?

 

[diablos991]

There are alot of factors(mainly wear and tear), including headgasket wear, valve wear, ring wear, and camshaft wear. Incorrect timing can also play a factor.
Your next step towards solving your problem should be the boost leak test. I wouldn't worry about 20psi on the leak test hurting your engine.

 

[oldman]

Tomorrow I will do the boost leak test at 15-18psi. What do you think that cause my engine to have low psi result?

If you truly performed the test with the car fully warmed up, throttle fully applied and battery fully charged, I would double check the results with another known good tester or compression test another car with your tester. In most cases when numbers are low but consistant across all four cylinder, the cause is the tester or testing procedures.

 

[The_one]

If you truly performed the test with the car fully warmed up, throttle fully applied and battery fully charged, I would double check the results with another known good tester or compression test another car with your tester. In most cases when numbers are low but consistant across all four cylinder, the cause is the tester or testing procedures.

I like your idea Oldman, i will perform a compression test on my bro's 97 gst and compare the result

 

[The_one]

There are alot of factors(mainly wear and tear), including headgasket wear, valve wear, ring wear, and camshaft wear. Incorrect timing can also play a factor.
Your next step towards solving your problem should be the boost leak test. I wouldn't worry about 20psi on the leak test hurting your engine.

Ok, I will do it tomorrow.

 

[The_one]

If you truly performed the test with the car fully warmed up, throttle fully applied and battery fully charged, I would double check the results with another known good tester or compression test another car with your tester. In most cases when numbers are low but consistant across all four cylinder, the cause is the tester or testing procedures.

I don't know this sounds logical or not? Let's say if it's a bad tester than it shouldn't response to the wet compression test at all. But i don't know i should perform the test on my bro's car to make the evaluation.

 

[diablos991]

It could still be a bad tester. The tester may just give out lower readings than it is supposed to.

 

[oldman]

I don't know this sounds logical or not? Let's say if it's a bad tester than it shouldn't response to the wet compression test at all. But i don't know i should perform the test on my bro's car to make the evaluation.

A bad tester usually means it leaks or the gauge is off, both cases will still respond to a wet test. Sure there are many things that will cause low compression, I just think that, with rings out of the way, the probability of every cylinder having similar degree of damage is fairly low. The only other possibility is that the timing belt is off enough to lower compression but not enough to bent valves.

 

[The_one]

A bad tester usually means it leaks or the gauge is off, both cases will still respond to a wet test. Sure there are many things that will cause low compression, I just think that, with rings out of the way, the probability of every cylinder having similar degree of damage is fairly low. The only other possibility is that the timing belt is off enough to lower compression but not enough to bent valves.

My bro did his compression and his result was 130 psi on all 4 cynlinders and his car is running and in good condition too. Also, feels more powerfull than mine. I think something wrong with the boost test device

 

[oldman]

Don't assume, next step would be to get a free compression tester rental from pepboys and retest.

 

[The_one]

Don't assume, next step would be to get a free compression tester rental from pepboys and retest.

Ok i will do that tomorrow or later this week,

thanks