The cylinder #3 is black and #4 is slightly black while #1 and #2 are clean. Spark plugs have been replaced but to no effect. I swapped the coils on the spark plugs but no difference either I believe, also did a valve adjustment and will recheck #3 and #4 again soon. It's been a few thousand km between tests for each change performed.

Any idea what to check for? I don't have a compression checker so I could do that next I guess.

Civic coupe 1.7L Si (Canadian).

 

The white you see doesnt actually mean its clean, the white indicates a lean condition the black is normal. You should see if the ignition is adjustable if not you could have dirty injectors causing it to run lean on those two cylinders.

 

I couldn't check the compression even though I have the tester because it is a hose type and I wouldn't be able to get it into and out of the engine block (actually got stuck the first time). I already did the valve adjustment a few days before this work and not seeing any improvement in the situation which is why I took that picture. Anyway it'd be nice to just see what the compression was like before and after the adjustment but it's too late now.

I replaced the engine to exhaust manifold gasket since I had the exhaust manifold off to replace the gasket between the exhaust manifold and the exhaust anyway. I then pulled the 4 injectors and had them tested at an injector testing company, KW Fuel Injection, in Waterloo for $25 and they checked out to be good. I reused the o-rings with a little engine oil because I couldn't get a good set to match the 2 different sizes of the top/bottom of the injector and so far there is no observable leaks.

When I reinstalled the injectors I swapped the order in which the came out (I marked them on removal) so that 1-2-3-4 became 3-4-1-2 (swapping the left half with the right half of the engine's injectors) to get a complete mismatch and confirm which injector isn't working. That is swapping the position and not the wires btw.

After a week of driving the car about 1000 KM the situation looks better. I haven't pulled off the exhaust manifold again to observe it but I can see from the spark plugs the situation looks better with the spark plugs for those 2 cylinders no longer turning black and all 4 are looking good.

 

I got you, it could be the #1 and #2 are running lean when they shouldn't be. But it was way too rich and coating the spark plugs, even though our engines run slightly rich, I could smell lots of fuel on the plugs which where new and totally blackened on #3 and not so much on #4 which I take as not so good news because 3 of 4 looked good with #3 looking really bad. If all 4 had been similar I'd have left it as it was but having the difference caused me to do some investigation As it turned out all the injectors are good (spray pattern, CC) and not leaking either. I guess to really know I'd have to see what a good car looks like for this 1.7L and 250000 KM (155000 Miles).

I don't know if there is a bad valve seal on that #3 cylinder, if it is it isn't serious yet because I don't think that I'm burning through much oil at all but just have to monitor it.