Did a compression check. Thoughts?

[beyondloadedSE]

As some of you have seen or heard, my engine burns oil...well something is burning oil. I thought it was oil dripping down into the spark plug holes from bad valve cover gaskets, but ive since fixed that and the problem still persists. I generally have to add a qt of oil every 300 miles or so. Its burned oil since day one when I fired it up. In my opinion, it has slightly gotten worse though.

I did a compression check this weekend and here were the results:

Cylinder 1: 120 psi
Cylinder 2: 120 psi
Cylinder 3: 120 psi
Cylinder 4: 125 psi
Cylinder 5: 100 psi
Cylinder 6: 120 psi

Im not really sure what to think about the cylinder with 100 psi. Not extremely terrible, but again, its lower than the 10% difference that everyone says it should be with in. I should have done a compression check the day the engine fired up, so I could have known if this is a new problem. At this rate, im hoping the turbo seals on the turbo are bad and thats what been causing the oil consumption.

To me, my hp/tq numbers do seem to be down, unless the non svt cams are just robbing me of power. SZ 05, put down 364 whp, 410 wtq with a pull to 4,700 rpms. Stazi read the boost at 16 psi. Could have been higher..who knows. He was the only witness. This year, I make 354 whp, 350 wtq @ 14 psi with a clean pull. Not really sure what to think.

Anyone have any ideas what might cause a cylinder to lose about 20-25 psi of compression? Cracked ringland? Would this cause that much oil consumption? Any thoughts are welcome.

[fastcougar]

Anything below 170 is something to start worrying about. Looks like maybe you got the wrong piston rings or maybe the machine shop didn't measure the pistons before boring and simply "bored to spec" and the pistons where "on the small side" of the spec

[Keyser]

Jim was your throttle body open when you did the compression test? It can make a substantial difference.

[fastcougar]

Jim was your throttle body open when you did the compression test? It can make a substantial difference.

How so ... most gauges build "peak pressure" over multiple compression strokes when both valves are closed. How I ran my tests:

1) Remove spark plug and screw in compression tester
2) Pull connector from coil pack
3) Pull fuel pump relay/fuse
4) Crank engine for 10 seconds
5) Take reading

My tester has a peak hold function and when I'm done, I simply jot down the reading, press the button to releave the pressure in the tester and then move onto the next cylinder.

[Keyser]

If you suck all the air in the intake manifold out, and the blade is closed, will it not lose momentum during cranking? On a 2JZ engine it can make a 20psi difference.

Edit: I believe Terry Haines made the same reference in the old forums as well.

[warmonger]

As some of you have seen or heard, my engine burns oil...well something is burning oil. I thought it was oil dripping down into the spark plug holes from bad valve cover gaskets, but ive since fixed that and the problem still persists. I generally have to add a qt of oil every 300 miles or so. Its burned oil since day one when I fired it up. In my opinion, it has slightly gotten worse though.

I did a compression check this weekend and here were the results:

Cylinder 1: 120 psi
Cylinder 2: 120 psi
Cylinder 3: 120 psi
Cylinder 4: 125 psi
Cylinder 5: 100 psi
Cylinder 6: 120 psi



Im not really sure what to think about the cylinder with 100 psi. Not extremely terrible, but again, its lower than the 10% difference that everyone says it should be with in. I should have done a compression check the day the engine fired up, so I could have known if this is a new problem. At this rate, im hoping the turbo seals on the turbo are bad and thats what been causing the oil consumption.

To me, my hp/tq numbers do seem to be down, unless the non svt cams are just robbing me of power. SZ 05, put down 364 whp, 410 wtq with a pull to 4,700 rpms. Stazi read the boost at 16 psi. Could have been higher..who knows. He was the only witness. This year, I make 354 whp, 350 wtq @ 14 psi with a clean pull. Not really sure what to think.

Anyone have any ideas what might cause a cylinder to lose about 20-25 psi of compression? Cracked ringland? Would this cause that much oil consumption? Any thoughts are welcome.

A cracked ring land would definitely cause about that much loss and burn lots of oil. That is what mine did and my compression was probably 30psi lower in those cylinders.

Even with 8.5:1 compression I'd expect it to be higher anyway. I'd think 150ish maybe?
Well anyway, it can still make decent compression and burn oil.
I think at 10:1 on my engine my compression was all in the 170-180psi range.

The first stroke would hit probably 120 the second bring it up to 150 and the third or fourth would hit towards 180. This is done as Jim said with the throttle open.

If you didn't test yours that way then maybe you should try it again that way and compare.

[Y2KSVT]

How I ran my tests:

1) Remove spark plug and screw in compression tester
2) Pull connector from coil pack
3) Pull fuel pump relay/fuse
4) Crank engine for 10 seconds
5) Take reading

My tester has a peak hold function and when I'm done, I simply jot down the reading, press the button to releave the pressure in the tester and then move onto the next cylinder.

This is essentially the same thing we did with Jim's compression test. I don't know if he pulled the fuel pump relay/fuse, but I don't see that making any difference. Sure enough, we tested that one cylinder twice, and it wouldn't go any higher than 100psi. All others were in the 120 range.

Mark

[Keyser]

I hate compression tests anyway. Do a leak down a find out for sure.

I believe the cam will make a significant difference in compression numbers, but for reference, my factory spec on my 8.5:1 engine is 125-165 cold.

Which brings up another point. Was the engine hot Jim?

[fastcougar]

Doh! Forgot about you having 8.5:1 CR and would account for lower readings across the board.

[beyondloadedSE]

I hate compression tests anyway. Do a leak down a find out for sure.

I believe the cam will make a significant difference in compression numbers, but for reference, my factory spec on my 8.5:1 engine is 125-165 cold.

Which brings up another point. Was the engine hot Jim?

Yes, the engine was hot...hot enough to burn my pinky finger on the rear valve cover while trying to pull off the spark plug wire.

I guess I'll have to give it another go with the TB open this time.

I suppose I should do a leak down test instead too.