engine compression results Options

[LewFX]

I decided to try a engine compression. So i got a free loaner from autozone. got home. and the results are...

1: 150
2: 150
3: 135-140
4: 155

i know 150 is good, but what about the 135?

This post has been edited by LewFX: Mar 24, 2007 - 4:34 PM

[alltracman78]

Well, first off

Did you
have all 4 plugs out?
have the TB wide open?
Crank all 4 cyl the same amount of times [4 is recommended]?

The most important thing with a compression check is that all cylinders are close to the same number.
Usually 10 - 15 PSI difference is considered the limit.
What number you use depends on who you talk to, and how picky you want to be.

You can put a tablespoon of oil in the #3 cyl to see if the rings are worn.
If they are, the reading will come up considerably [it will come up some regardless].

If this yields nothing, you can either leave it as is, or do a leakdown test.
That's a bit more complicated, and you will need shop air. you can't just to it in your driveway with a gauge [unless you have an air compressor hooked up].
Doing this will tell you exactly where the cylinder is leaking from.

Keep in mind carbon buildup in the cyl can effect the readings also....

[LewFX]

Did you
have all 4 plugs out? no
have the TB wide open? no
Crank all 4 cyl the same amount of times [4 is recommended]? yes

[alltracman78]

Ah.

Then you are best off redoing the test.
You can have someone hold the throttle open, or wedge it open.

[LewFX]

ooookay, test 2...throttle open
1: 115
2: 125
3: 120
4: 120

put small amount of oil in each cylinder...now she smokes up a storm, i mean allot and smells bad.

help!

reminds me when you put sea foam in and its smoking like mad, thats whats going on here

This post has been edited by LewFX: Mar 24, 2007 - 7:26 PM

[alltracman78]

The smoke is fine, and normal.
The oil will burn out.

Interesting that all went down. I don't know what to tell you there. Something else must have changed....
However, they are all closer, with a 10PSI difference across the board.

You didn't need to put oil in all 4, we were just going to see if it made any difference in cyl 3, which had the low compression.
Also, those pressures seem a bit low, especially with oil in the cylinder....

Why don't you drive it around and burn off the oil and try it again to see what it has?

This is if you are really worried about your engine.
IMO, unless you have a specific problem, there really isn't a need to do this....
How far you want to go is totally up to you....

[playr158]

why would you want to open the throttle?

[alltracman78]

So the engine can breathe.
It makes it easier for it to suck the air into the cylinder.

[Bitter]

did you disable the fuel system? gasoline will wash oil off the cylinder walls and give low readings. also did you check on a hot or cold engine? this test should be done with the engine at operating temp.

[alltracman78]

Ah yes

I knew I wasn't mentioning something, but I couldn't remember what it was....

Disconnect your crank sensor. This will cause the ECU to not see the engine turning over, so it won't deliver fuel or spark.
And yes, it needs to be done on a hot engine.

[hurley97]

so don't freak out when your CEL comes on afterwards. that happened to me and I sort of freaked out for a while. reset it and its fine

[LewFX]

first test was done with hot engine, second i let cool down but warm up for 5 minutes

[alltracman78]

You want it fully hot.
Let it get up to operating temp. This might have been why the readings were lower....

Also, you can pull your EFI fuse instead of disconnecting your crank sensor.
Either will do. You will have to pull the fuse regardless to clear the codes [or use a scanner]. Easier to acess than the sensor connector too.
I do the crank sensor out of habit. Alot of newer cars have throttle by wire, so you need the ECU powered to open the butterfly valve.

[LewFX]

o well, car seems fine, just curious about the compression...already took the tester back