Low Compression in one cylinder only
 

2003 civic lx 1.7L, 187,000 miles. The CEL light came on. Scanned it and got a misfire in cylinder #3 code.

Pulled the plugs, #3 looked slightly more oily than the others. All four were white on the tips and electrode. These plugs are NGK 169Iridiums and have 17,000 miles on them.

Compression test results:

#1 210 dry
#2 220 dry
#3 135 dry
#4 220 dry

A few drops of oil in #3 increased it to 140, but no more.

Compression test from 17,000 miles ago when the plugs were replaced just for comparison:

#1 204 Dry 222 w oil
#2 210 Dry 227 w oil
#3 205 Dry 207 w oil
#4 210 Dry 230 w oil

Switched #1 and #3 coil just for the hell of it, cleared CEL and it has not come back on in 20 miles. Idle is slightly shakey but not too noticeable.

Car has 187000 on it. #3 cylinder seems to be going south. What do you guys recommend?



Some more relevant history about the car:

Head Gasket; No problems here:
I've been keeping an eye on the coolant. The radiator remains full and the reservoir is not overflowing. No coolant leaks, heater works perfect. Head gasket was replaced 62,000 miles ago. No problems with coolant level in radiator since then.

Oil Useage:
I've had the car since it had 48,000 miles. It never used a drop of oil until about 125,000 miles when I switched to full synthetic. Oil consumption has steadily increased. It now uses a quart every 1200 miles.

Re: Low Compression in one cylinder only
 

why try to fix what isnt broken?

why pay more for synthetic when your previous oil was doing fine?

these are things i just dont understand,

burning a quart every 1200 miles is a heck of alot, my engine wouldnt burn that much in 25,000 miles

Re: Low Compression in one cylinder only
 

Stupid f****n synthetic!!! Why did I switch????? Arrghhh!!

Re: Low Compression in one cylinder only
 

Check valve clearances.

Recheck compression.

If no improvement: Leakdown tests.

Possible valve issue on #3?

Re: Low Compression in one cylinder only
 

Ok will do, I'll check and adjust the valves and report back.

I did check and adjust them about 20,000 miles ago. It's entirely possible I messed up and left an adjustment screw or two loose.

Re: Low Compression in one cylinder only
 

Here is an old picture of the head immediately after removal when I did the HG 60,000 miles ago.

I just noticed #3's exhaust valves are darker in color than the others. Not sure if that was a sign of impending trouble that I failed to notice at that point.

Re: Low Compression in one cylinder only
 

Dang, you have the head off already?

.......

EDIT: Nevermind, just now saw 60k ago.

Re: Low Compression in one cylinder only
 

Synthetic oil has nothing to do with problem. Did you replace HG 60K ago from overheating. Hopefully, it's a too tight exhaust valve. Think you would hear too loose and a too tight intake would be noticed in intake system. Those little lock nuts do not take much for torque and its probably easier to strip one then leave loose.

Re: Low Compression in one cylinder only
 

I agree, blaming synthetic oil for a problem without having any idea what caused it makes no sense.

I also question your wet compression reading for #3. A "few drops" may not be enough oil to determine if the rings are the cause or not. Most people say 1 to 2 teaspoons.

Re: Low Compression in one cylinder only
 

Just checked the valves. The intake valves were a tad too tight. I had too much drag using the .007 feeler gauge so I readjusted them. However, they were similarly tight on all four cylinders, not just #3, so i'm leaning towards a bottom end problem.

Leak down test next. I'll have to buy an air compressor. Is 100 PSI enough?

Re: Low Compression in one cylinder only
 

Not unless or until further testing points that direction.

Note leakage % if using a real leakage tester, and note where air escapes to. Leakage into the crankcase is always present, you have to judge by comparing between known good cylinders and suspected bad.


"A few drops" might not have been sufficient quantity do perform that test.
A tablespoonfull instead?
Use too much and it falsifies readings very high, or if you don't spin it over with the plugs out several times first can hydrolock the engine and bend a rod. (Someone who posted here long ago skipped that important step, and may have cost himself an engine)

Re: Low Compression in one cylinder only
 

Update: I don't have a leak down tester but I was able to preassurize #3 with a slightly modified compression testor hose. I used 100 PSI.

On a warm engine with #3 at TDC compression stroke, NO air leakage could be detected anywhere. BUT as the engine cooled down and I repeated the test, air started leaking down past the rings into the crank, I could hear it clearly in the oil fill hole.

I then tested the remaining good cylinders at this and they all leaked into the crank but #3 was the "loudest" leak which I guess makes sense because it has the lowest compression (135, the rest all around 205).

Next test resulted in a very strange observance. This was done the next day after I drove the car then let it cool down for an hour. This time I removed all 4 plugs first then placed #3 at TDC compression and applied 80 psi air to it. It leaked again, but this time I saw white smoke being pushed out of number #1's plug hole!! Wtfff??

I can only guess this smoke was remnants of blow-by still inside the crank. The pressurized air probably leaked past #3's rings, pressurized the crank and #1 happened to be low enough that blow by escaped through. I never knew #3 and #1 are linked in this manner.

Anyway, looks like I have some ring issues with all 4 but #3 is the worst. Not sure if it's the oil control rings or the other piston rings.

I'm doing a marvel mystery oil soak in all 4 right now.

Do you hear noice at intake or exhaust port, side (mufler, air box ) ?

Re: Low Compression in one cylinder only
 

Nope, checked all these locations. Nothing. Then rotated the crank so that exhaust valve opened, just to see what it would sound like. Similarly "forced" a leak into the intake. It was pretty easy to hear the difference. I'm pretty certain at this point the valves are good.

Re: Low Compression in one cylinder only
 

Brief glimpse, gotta run

Huh? It wouldn't come UP through the rings on #1 but none of the others, and anything that went into the crankcase would exit through the valve cover vent tube or open oil cap long before trying to worm its way UP a full set of rings. Unless there are huge honkin gaps in the rings, which isn't supported by the compression readings on anything but #3.

Probably was just fuel vapor, there wouldn't be any smoke available on a halfway cooled engine.

A little valve leakage from the pressurized cylinder (#3) could cause what you saw to happen....seems like the exhaust valves would be partway open on #1 while all valves on #3 are supposed to be closed.



I posted yesterday somewhere, you need to screw 3 spark plugs back in while pressurizing a cylinder looking for valve leakage. Air leakage past any valve during a test can and will escape through other cylinders that have open valves, and that might be why you didn't notice anything at the tailpipe or throttle body. Gotta plug up the wide open holes with the spark plugs.

I sometimes strap a blue glove over the tailpipe and TB throat, then see if either glove tries to inflate when air is applied to cylinders.

Re: Low Compression in one cylinder only
 

Now I feel dumb! Lol! This sounds like a much more plausible explanation. It sounds like I might have a leaky exhaust valve on #3. Also seems to confirm that the intake valve on #3 is ok, (or at least better sealing than the exh valve), else I would have seen that same fuel vapor smoke coming out #2, since #2's intake valve should be partly open when #3 is at compression TDC.

I'll repeat the test with remaining plugs in this time and listen carefully for a leak at the exhaust pipe.

Re: Low Compression in one cylinder only
 

Duct tape big sammich bag to the tailpipe ...a leak should make it inflate like a balloon....maybe slowly if leakage is slow but it would be visual confirmation nonetheless

Re: Low Compression in one cylinder only
 

Its the exhaust valves on #3.

I duct taped a samich bag onto the tail pipe, plugged the remaining three cylinders and pressurized #3. The bag inflated.

The picture of the head I posted earlier shows that #3's exhaust valves are kinda burnt looking so not too surprised I guess.

Is a new head next or is it the same to get new valves in this one?

Re: Low Compression in one cylinder only
 

I can't tell you prices. Ask at your local machine shop how much the valve job will cost, figure probably at least a pair of valves along with it.