I want to cry... compression

[Nanan]

My car has been running great for a long time, guess it was to good to be true. Today on my way home from work it started running rough like a piston was missing. I pulled the plugs and all but number 3 looked good. Number 3 looked dark black with a bit of white ash on it.

Compression test:
#1 = 170
#2 = 170
#3 = 130
#4 = 170

Wet test:

#1 = 175
#2 = 175
#3 = 160
#4 = 175

The head was rebuilt ~20k miles ago so I expected ok compression across the board.
Well it looks like Ill be tearing apart the engine after finals next week to see whats gone wrong.

 

[rowlex]

My car has been running great for a long time, guess it was to good to be true. Today on my way home from work it started running rough like a piston was missing. I pulled the plugs and all but number 3 looked good. Number 3 looked dark black with a bit of white ash on it.

Compression test:
#1 = 170
#2 = 170
#3 = 130
#4 = 170

Wet test:

#1 = 175
#2 = 175
#3 = 160
#4 = 175

The head was rebuilt ~20k miles ago so I expected ok compression across the board.
Well it looks like Ill be tearing apart the engine after finals next week to see whats gone wrong.

sucky, when my car does that im just gonna try to re-ring it

 

[psychlow]

Sucky....

White ash usually indicates you're running lean or too hot. It might be black now from misfiring....

Sounds like the rings based on the wet test.

 

[Nanan]

I am guessing that the #3 injector is going so the car has been running lean on #3. Its likely that my exhaust valves and rings are burnt.

 

[92awddsm]

I have seen this before and Im sure you didnt burn a piston or valve with that high of compression. Before you tear it down, get some mccc and run through the engine. The reason I say thiis is because I have seen the rings get gummed up and stick in the piston. After a good cleaning, compression went back to where it is supposed to be. In one case, it was so bad that I had to pour a little atf into the cylinder and let it sit over night to free up the rings. It is worth a try in your situation and only cost a few $. Thats alot better and cheaper than a tear down and worst case senario, it doesnt do you any good.