IO-360-A1A Cold Cylinder Past Idle

[drone_pilot]

Today when running my engine, the #4 CHT and EGT matched the other cylinders at idle. When running the RPM up to around 1100, the #4 CHT and EGT drop off to basically nothing. Pulling the throttle back to idle the #4 CHT and EGT come back to normal temps along with the other cylinders. The engine is very rough when the temps drop off so very clear the #4 isn't firing.

The only thing I can think of is a clogged #4 injector. Does this sound correct?

With all of the fuel filters, etc, what would clog an injector?

[Carl Froehlich]

In the order I'd trouble shoot:
- Ignition, harness and spark plugs
- Stuck exhaust valve
- Bad/dirty injector
- Spider crud problem

Carl

[PilotjohnS]

I would also look at the sensor, maybe a loose wire or bad sensor?

[drone_pilot]

I don't think it's a sensor as the motor is running rough and both EGT and CHT sensors on the same cylinder are affected by low readings that would correspond to a dead cylinder.

[BillL]

It could be something complicated, but it is easy enough to check that injector, then move to more complicated possibilities. Still thinking fuel, the spider could have a speck in it too. Might have to measure some flow on the injectors too - just to complete the "low fuel" possibility .

Hard to think both mags are weak on the same cylinder or one bad plug and bad mag on the other.

Please post your findings.

[drone_pilot]

Okay. I couldn't stand it so went out to airport to check the injector. One thing I forgot to mention is that it's a new build, so it hasn't run but a couple of hours.

I removed the tube at the divider for cylinder #4 and got a cup full of fuel when running the boost pump. I removed the tube at the injector and got another cup full of fuel. I removed the injector and found it was plugged. Took a fine piece of safety wire and ran thru the injector. It appeared to be a few particles of black rubber fuel hose, which makes sense because a guy at the airport made me a fuel hose from the mechanical pump to the servo. There are so many filters in the line that I don't know of another source that it could have come from.

Since I found debris in the injector, I went back to the flow divider and took it apart. Sure enough, two more small particles of what appears to be black rubber. I ran fuel thru the divider while disassembled after removing the particles. I blew the injector and flow divider regulator stem (whatever it's called....the part connected to the diaphragm) with compressed air and verified all was clean before reassembling. I ran out of time but I am going to remove the other three injectors and verify that they are not contaminated as well. The injectors are tiny and it doesn't take much to plug them.

I did fuel flow testing about two weeks ago so I am also wondering if I got some crud in the lines while disassembled. I'll be watching carefully for a while to make sure everything stays clean.

[PCHunt]

I've never had an injected engine, but I seem to remember reading somewhere that you should never run a wire through an injector. Is this correct, or am I "mis-remembering"??

[rv8ch]

Originally Posted by PCHunt

I've never had an injected engine, but I seem to remember reading somewhere that you should never run a wire through an injector. Is this correct, or am I "mis-remembering"??

According to Lycoming, you are correct:

http://www.lycoming.com/sites/defaul...%20Nozzles.pdf

Originally Posted by Lycoming

CAUTION
Never use a sharp tool such as a wire or pin to clean out a nozzle. Damage to the inlet and outlet fuel restrictors could result which would change the fuel flow.
Do not immerse packing rings, at any time, into the cleaning fluid. The rings may swell.

[BillL]

Personally, I would deem it acceptable for discharge of obvious plugging debris, but never to do a routine cleaning for accumulated varnish.The wire end should be rounded from the cut, smaller than the orifice, and straight. Don't ram it back an forth. I have very tiny drill bits ( primarily for acetylene torch tips) and use the dull end, and don't force it. Skill and common sense applies, as with many delicate operations.

[ColoRv]

This sort of debris is common on new builds. It should be the first thing checked if a cylinder goes cold.