bad compression

[Alex7747]

So a couple days ago i did a compression test and it came out 110 a cross the board .. my question is, what are some tests to find the problem? i have (at idle) 20 psi of vacuum. is that normal..if i have such high vacuum and low compression?
i tried to perform a leak down test but I'm not really sure on how to even get a reading?.
I was going to do a wet compression test to check the rings but i heard somewhere that if the oil is poured into the cylinder and it stays on the piston (i have the stock 2g pistons so their like bowls) the readings would be point less..
so I'm looking on advice on how to diagnose my low compression . the car still pulls okay but i would really like at least 160 psi. so i need help...
oh yeah i read that foam in the coolant could mean a bad head gasket? how could i check for this? (the bad head gasket, i have foam in the coolant).

Thanks ahead of time
oh and one more thing, when the cars at idle and i remove the oil filler cap i can feel a lot of air coming out if hold my hand over the hole. any thoughts?

 

[awdjosh]

Well you should double check your compression again with a different compression gauge to confirm if the first results are right. With it being 110 across is alittle weird as it normally is off on a couple cyclinders or all over the place with numbers.

 

[gusu]

You have 20 PSI of boost or you have -20 inhq? -20 is a totally normal number.

I think you did the compression test wrong some how. Bad gauge?

 

[awdjosh]

Blowing a head gasket on all four cyclinders I don't even think it would run haha

 

[Tyeler18]

Normal engine wear will yield even numbers on all 4 cylinders. My 172k 6 bolt had 100psi across the board, all from normal engine wear. If the headgasket blew you will have odd numbers between cylinders GENERALLY. Is their oil in your coolant? How many miles on the motor. Other than the foamy coolant your compression numbers sound normal for a higher mileage 4g.

 

[rlacasse1]

Go buy a leak down tester and do a leak down test on it and that will show you exactly what is leaking.

If you have muddy looking oil or coolant then it could be your head gasket that is bad.

You can try pulling off the radiator cap and seeing if it shoots coolant out when you crank it, that would be indicative of a head gasket. But since you have even compression across the board I would say it is your rings. When you do a leak down test if you get a lot of air flowing out of the oil fill cap then that is a good sign your rings are shot.

 

[Calan]

You can try pulling off the radiator cap and seeing if it shoots coolant out when you crank it, that would be indicative of a head gasket.

Coolant "shooting out" while just cranking would be indicative of the most monstrous and strangest head gasket issue in history.

A few air bubbles while idling would be much more likely.

*********


http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html
http://www.dsmtuners.com/forums/articles-engine-fuel/336535-do-you-have-blown-head-gasket.html

 

[BogusSVO]

Was the engine warm when you did the compression test?
Did you pull all 4 spark plugs whan you did the test?
Was the TB fully open when you did the test?

Also check your time belt and make sure all time marks line up properly.

 

[skatershawn]

About the oil cap, crank pressure is normal, you will see some venting through that or the pcv, ect.
However to much at idle may be signs of bad valve seals or the like, which can cause low results in a Compression test.

Retest your compression, make sure the car is at normal operating temps, pull all plug, do one at a time and make sure you have the gas paddle all the way down (throttle body valve 100% open) while doing the 5 cranks! (FYI incase you didnt know)

Once you do that again and if you get low results I recommend you to do a leak down test to pin point the loss of compression!


Edit:
I love it when the Wisemen post while i'm typing haha!

And thanks to Calan, I was looking for that link to your Write-up(Great Write-up BTW), I just read it yesterday night as I have inconsistent readings and was planning to do a leak down test!

 

[Calan]

I love it when the Wisemen post while i'm typing haha!

According to my browser, Bogey and I both posted around 9:00am; you posted at 10:13.... and I thought I was slow at typing!

And thanks to Calan, I was looking for that link to your Write-up(Great Write-up BTW), I just read it yesterday night as I have inconsistent readings and was planning to do a leak down test!

Thanks. I'm glad you find it useful.

 

[skatershawn]

According to my browser, Bogey and I both posted around 9:00am; you posted at 10:13.... And I thought I was slow at typing!



Thanks. I'm glad you find it useful.

haha.. ok well I had the window open then got caught into my work! (FYI i'm at work!) shhhh!
And I never refreshed the page, so sorry about that!

 

[Calan]

Just bustin' your chops.

 

[Alex7747]

well the engine only has about 1500 miles on the rebuild thats why I'm confused.. i didn't hone the cylinders though, but they still had some cross hatching.
the oil and coolant arent mixed at all. so i don't know if its the head gasket. what would it mean if the coolant is foaming?
I'm thinking its the rings or i need to hone the cylinders.
My compression tester is brand new so i don't know if its bad or not. but I'm sure its working.
ill try to find a leak down tester and do a leak down test.

You have 20 PSI of boost or you have -20 inhq? -20 is a totally normal number.

I think you did the compression test wrong some how. Bad gauge?

sorry I meant i have -20 inhq(idk if thats right?). but the reason i asked if it was normal is because if i had bad rings, would it still have good vacuum?

 

['97boostinGST]

^^^
Vacuum is not affected by compression. Before I got my car done I had compression readings of 90,130,150,160 and vacuum still read -20 Hg.
What exactly do you call a "rebuild" if the block was not honed?
Was the car at full operating temp and plugs out like already mentioned?
Did you slowly break in the new motor or just drove it like whatever?

 

[Alex7747]

^^^
Vacuum is not affected by compression. Before I got my car done I had compression readings of 90,130,150,160 and vacuum still read -20 Hg.
What exactly do you call a "rebuild" if the block was not honed?
Was the car at full operating temp and plugs out like already mentioned?
Did you slowly break in the new motor or just drove it like whatever?

it spun a rod bearing so i got a new oil pump, new crank, pistons, main bearings, rod bearings, and all the gaskets.
the car was at full operating temps. all the plugs were out. the fuel system was not connected.
i broke the motor in the street bike way. i did a couple of 3rd gear pulls and slowed down real fast. then i just drove it like i would normally drive the car.

Was the engine warm when you did the compression test?
Did you pull all 4 spark plugs whan you did the test?
Was the TB fully open when you did the test?

Also check your time belt and make sure all time marks line up properly.

the engine was at operating temps. the plugs were all out. the tb was closed the first time i did the test and i got about 110across the board then i retested it with the tb fully open and i got the same readings. 110 a cross the board.

 

[Gasolinebaptism]

Did you have your foot to the floor while cranking during the compression test?
This cannot be stressed enough.

 

[Alex7747]

Did you have your foot to the floor while cranking during the compression test?
This cannot be stressed enough.

yes the throttle body was FULLY open on the second test.

 

[Boostinsideways]

How many miles on teh rebuild? Its possible the rings are not seated yet.

 

[Gasolinebaptism]

Is it smoking? If not then I wouldn't blame the rings.
And did you use conventional oil and not synthetic?

 

[Alex7747]

How many miles on teh rebuild? Its possible the rings are not seated yet.

about 1500 miles

Is it smoking? If not then I wouldn't blame the rings.
And did you use conventional oil and not synthetic?

no theres no smoke. i used conventional oil in the first 1000 miles but now its synthetic.

 

['97boostinGST]

it spun a rod bearing so i got a new oil pump, new crank, pistons, main bearings, rod bearings, and all the gaskets.
the car was at full operating temps. all the plugs were out. the fuel system was not connected.
i broke the motor in the street bike way. i did a couple of 3rd gear pulls and slowed down real fast. then i just drove it like i would normally drive the car.

Hmmm...you slowed down "real fast" as in you stepped on the brakes to slow down?
Your supposed to let the RPM's drop, without braking!
I did this method for about 1k miles and my compression sits at a perfect 170 across. Now I'm at 1500 into the build and STILL using conventional oil. Im not going full synthetic into the 3k miles.
Did you perform any oil changes throughout the breaking in process?
If so, how many?

 

[Alex7747]

Hmmm...you slowed down "real fast" as in you stepped on the brakes to slow down?
Your supposed to let the RPM's drop, without braking!
I did this method for about 1k miles and my compression sits at a perfect 170 across. Now I'm at 1500 into the build and STILL using conventional oil. Im not going full synthetic into the 3k miles.
Did you perform any oil changes throughout the breaking in process?
If so, how many?

it wasn't super fast but yeah after i accelerated i slowed down using the brakes.
i changed the oil out at about 50 miles, then 500 and then recently like at 1400.

 

[Anubis_4_99]

in my opinion, you need to pull the motor apart again, and properly rebuild it. that means new rings again, and honing the block like you should have done the first time.

expecting good numbers from a block you do no machine work to just isn't realistic.

 

[Alex7747]

in my opinion, you need to pull the motor apart again, and properly rebuild it. that means new rings again, and honing the block like you should have done the first time.

expecting good numbers from a block you do no machine work to just isn't realistic.

yeah i think so too.

 

[rlacasse1]

Coolant "shooting out" while just cranking would be indicative of the most monstrous and strangest head gasket issue in history.

A few air bubbles while idling would be much more likely.

*********


http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html
http://www.dsmtuners.com/forums/articles-engine-fuel/336535-do-you-have-blown-head-gasket.html

Uh, not quite. If you have a blown headgasket, it will SHOOT coolant out of the cap.

Example's:

Buddies civic had coolant dripping off the ceiling of my garage after he cranked, not started, it with the cap off.

My s-10, coolant all over the engine bay and hood after cranking, not starting, it with the cap off.

That is just a few of the many that I have seen do this.