I recently replaced theree injectors. I had a misfire that was greatly improved by the replacement.

Before this swap I ran my mix at the clockwise extreme setting. This was better than any other setting, which caused worse running.

After the swap I am running my mix at the extreme counter-clockwise extreme. Any other setting causes increased missing.

I can state with fairly good confidence that I am missing on only one cylinder and not constantly, but steadily. Perhaps every other or 2 out of three.

When cold started, it runs much more smoothly. A miss on occasion but more on the order of 1 in 10. Still isolated to one cylinder. This worsens as the engine warms.

Obviously I need to resolve which cylinder. But I’m trying to understand what is going on here. I see that the mix affects the miss. So I assume it’s running near the edge of acceptable fuel air ratio.

My presumption before. The injector swap was that I had one injector not delivering sufficient fuel to fire, the O2 sensors saw the free oxygen in the unburnt charge and riches up the mix to fix it. Running my mix rich helped this cylinder and thus the correction was reduced or happened less frequently.

to be honest, I’m not sure which direction is lean vs rich. Experimental results and just based on improvement.

I plan to go through the injectors disabling one at a time to determine which is problematic this weekend.

Anyone have any input on this situation?

Thanks Warren, I do want to determine which one is still under-performing. Perhaps some debris in the screen. But all 12 are new.

I appreciate the method suggested. Sometimes it really is harder to pinpoint a miss on the V12. Pulling a whole bank out is a great idea. Did you start it on 6 too, or D/C the injectors once it was running?

I think I’m might pull the whole rail, connect up my test pump/regulator setup and signal generator. Run each one for 1000 cycles and do a volume check.

Cranked my fuel pressure up to 42psi this morning. Really close to proper idle. Closer that I’ve ever gotten. Need to buy an O2 analyzer and see where it’s actually at. I know there is a method of using the O2 sensors output to do so, but I can’t recall where I saw the method written up. EDIT:found it.