The Unabageler

when I took off the head nothing looks out of the ordinary. I have no clue why my compression is low on 3 cylinders.

symptoms: detonation and backfiring. Friday, twice on my way to work the engine cut out like I wasn't getting fuel or spark. My gas pedal felt very heavy. Restart the car and things were mostly fine. I got to work, took out the plugs and saw #2 spark plug lost the electrode and was backing out, carbon buildup all over my #2 coil. Replaced the plugs. On my way home, car cut out once more. Get home and it smells like burning oil. Let the car sit all weekend. Tuesday morning I did a compression check and #2,3,4 were 160-175. Removed cylinder head, all valves look normal, pistons look normal, cylinder walls are smooth but the sleeves on #1 and #4 are starting to show minor signs of wear (65k engine with lots of track time and a few overrevs)...but nothing major that would be causing compression leak.

Should I go ahead and drop the oil pan so I can check my piston rings? This is my first time taking an engine apart so any troubleshooting advice you guys can offer would be excellent and most appreciated.

ultimate lurker

1. What was the compression on #1?

2. Did you do a leakdown test?

3. Did you try adding oil to the cylinders to see how much the compression improved?

Its often hard to see if a valve is sealing properly. Doesn't take much of a dink to screw up compression. The fact that a plug was backing out is not good news, but if you're compression is down on 3 cylinders, something else may be going on.

UL

krazik

Compression was:

Cyl 1: 210
Cyl 2: 155
Cyl 3: 160
Cyl 4: 170

No leak down test was done.

s-duces

was the each cylinder getting proper air and fuel supply?

s-duces

if so check the injectors... too much fuel the plugs wont spark too little fuel the plugs will burn out

The Unabageler

s-duces, i think you failed to read my post.

ultimate lurker

W/O a leakdown test its hard to say if the valves were damaged. The fact that three cylinders are down tells me it is probably something to do with a misshift, but even that is still a WAG.

Putting oil in the chambers before a compression test will usually raise the compression numbers. Cylinders with worn rings will come up more than those with good rings. If the three down cylinders got closer to the good cylinder, I would have pointed at ring issues, but putting the head back on for a compression test is a bit of a PITA.

UL

The Unabageler

I have had a misshift and a separate mechanical overrev in the past 3 months. no engine trouble after the misshift (my clutch absorbed it all and broke) but this trouble started coming up after an overrev (downshifting at the track, but with no brakes i let out the clutch a little early).

The Unabageler

the piston heads look great, so my last two guesses are valves or rings. i'm going to replace all the valves now anyway since i have it all taken apart, but that still leaves the question of the rings. taking off the head wasn't hard at all, but dropping the oil pan etc sounds like a bitch that i'd rather steer clear of.

I should also note that the symptoms while driving were intermittent and I heard no knocking or ticking out of the ordinary. Idle was rough (go figure, only three plugs ), but then i replaced the plugs and it smoothed out.

The Unabageler

anything else I could be checking while i have the head off and waiting for new parts? head gasket will be here tues or wednesday...i haven't called joe yet about the valves, probably do that tomorrow.