Interesting Situation

[Derek]

IO-360, A4M, AFP FI

Whilst in the run up bay, just about to do my mag checks the engine developed a severe miss, Cylinder 3's EGT and CHT both dropped away to zero.

At approximately 1,000 rpm and with a bit of leaning i could get the Number 3 CHT up to about 150 degrees however if i tried to advance the throttle further the CHT would fall away to zero.

I shut down and restarted, immediately after restarting I noticed No. 3's EGT went straight up to about 1200 degrees way ahead of all the EGT's, meanwhile No. 3's CHT remained low.

I?m no expert, but here is my list of possibilities in order of preference.

1. Blocked injector
2. Induction leak
3. Stuck valve.

[Jesse]

First thing to try is turn your mags off and pull the prop through 4 compression strokes by hand. If they all feel about the same, then they all 4 are getting compression, so likely not a stuck valve. A clogged injector sounds very possible, running that cylinder so lean (high EGT) that it's not making much power (low CHT). An induction leak doesn't sound like it would do this if you are injected. Carbureted might look like this from a big induction leak.

[Derek]

Hi Jesse, thanks for your reply.

I removed No.3 injector nozzle and found a very small piece of debris stuck inside. This piece of debris is approximately 50% of the size of the nozzle exit hole. Its unique shape is the only reason that it hadnt passed right through.

Anyway ive removed the debris, checked all the other nozzles and went for a fly, all good. My engine is back to performing the way it always has been.

At this stage I dont know what the piece of debris is or where it came from.

[BillL]

Excellent diagnosis - listed in probability order, and successful. How in the world did something that big, get that far in the system?

Well done, thanks for the learning experience.

[Derek]

The only thing I can think of "out of the ordinary" is that a few days earlier I completed my first annual inspection, during this process I removed and cleaned the fuel filter. Its possible that the piece of debris was introduced into the fuel system at that time.