compression test. Not Good!!!!!!!!!!!!!

[91talon27]

I did a compression test today because my car hasn't been running good. I got #1-110 #2-130 #3-130 #4-130. The spark plug that came out of #1 the electrode is bent and the center insulator around the electrode is broken and missing. I am planning on pulling the head on Saturday or Sunday to see what all is damaged(needs replaced) and what I can save. I may just start from scratch and do a complete rebuild. Ie: Pistons, Rods, crank turned, block bored, new Arp studs everything. I haven't decided yet depends on what all is damaged I guess.

 

[talon187]

sounds like you have bent valves if you broke part of the spark plug make sure you resurface the head i would also use a mitsu 4 layer metal headgasket and remove balance shafts as well

 

[xveganxcowboyx]

Get a leak down test before rebuilding. It could be that the bottom end is in fine shape and it's just the head that needs work. In that case you'll save yourself a tom of time and money just having the head rebuilt.

 

[haioku-rocket]

Or a little getto trick that usually works for me.. squirt a little 20-50 oil down the cylinders, then test again. If it goes up a significant amount then you know you atleast have blow by and need a rebuild/rehone because the oil helps seal the rings on the bottom end. If it doesn't go up then chances are you are leaking out of the headside. This is not a 100% guaranteed method but has worked for me in the past. If you have access to a leak down tester then disregard and do it the right way.

Good luck.

 

[1992awdlaser]

Putting oil in the cylinders will always make the compression numbers go up. The oil will sit in the dish of the piston which will create lesss space for the air to occupy. Less space=higher compression ratio=higher compression

 

[snooopy365]

Putting oil in the cylinders will always make the compression numbers go up. The oil will sit in the dish of the piston which will create lesss space for the air to occupy. Less space=higher compression ratio=higher compression

yes... and with bad rings your just blow the oil through the rings.. so this test works well!

 

[1992awdlaser]

yes... and with bad rings your just blow the oil through the rings.. so this test works well!

Like I said, that so-called "test" will always make the compression numbers go up.

 

[snooopy365]

## not using a lot oil! you should use a few drops nothing more so add a few drops of oil with a syringe, than do the compression test.
do that with all cylinders.

normaly it should look nearly the same as before (without oil), if the numbers are higher at any cylinder than before (about 0.5-1Bar higher) ## rings are blown.

if the cylinders are still not near to euqil than ## head is the problem or the rings arn`t existing anymore.

 

[dsm-onster]

I've done this on several occasions and have been mystified myself at first. But, your compression will ALWAYS go way with the wet test.

If you personally go out and do a wet test on your car right now it will fool you into thinking you need a rebuild unless you know the factory specs and limit for compression psi. Mine is freshly rebuilt and broken in, so is my brothers. The compression reads in spec for both. Both show up to 30 psi or more after dropping in just a teaspoon of oil, albeit it will be over factory specs and these are 1g pistons originally showing 155 across the board.

The test doesn't work very well at all for dished pistons.

91talon27, the bits of the sparkplug MAY have scored the block. Did detonation occur? Usually, it's worse in the number 1 cylinder, from my experience. You could have dodged a bullet like me and the piston ring lands cracked, but no block damage.

Which maf are you running? a 1G maf? If so, I guarantee you're overrunning it. This will lean you out enough to melt stuff.

 

[91talon27]

I am running a 2G maf with a keydiver chipped Eprom.

 

[JusMX141]

I always used the "wet test" only to determine whether it was the valves or the rings that were not sealing properly- NOT how worn out the rings were.

Prior to rebuilding my girlfriend's Sunfire last spring, you could dump as much oil into the cylinder as you wanted and #2 still read 90psi.....which is how I diagnosed the head to be at fault and not the rings.

 

[dsm-onster]

^^^good point. The fluid will just squirt out of the leaking valves, if the valves are bent.