Cold Cylinder on New Engine

Mark Dickens · #1 10-27-2016, 06:33 PM

So, I and a buddy are at the airport this afternoon and decide to conduct a taxi test. At start up, everything is smooth as butter, but toward the end, my #4 cylinder basically went off line...very low CHT and EGT. We ran the engine up to 1800 and were able to get the CHT/EGT on #4 to come up, but as soon as we reduced throttle, it went away. I'm thinking clogged injector.

What say the experts?

Carl Froehlich · #2 10-27-2016, 06:58 PM

As this is a first run problem I recommend you look for less traditional causes. For example, the symptoms you discribe could be explained by the engine sucking in a bolt that gets suck under the intake valve holding it open. Look also to a loose intake pipe on #4 that is letting in air.

If you have a borescope you might want to look into #4 and its valve seats.

Injectors are easy to clean so do that. As I've seen this exact problem from a tiny piece of crud in the spider keep that on the list.

Good luck,
Carl

Carl Froehlich · #3 10-27-2016, 07:01 PM

I forgot to add - to check for a clogged spider do the shot glass test. Do the flow test at idle and at power. If #4 has less flow you have your smoking gun.

Carl

Mark Dickens · #4 10-27-2016, 07:06 PM

That was part of the plan for tomorrow. Got the AFP manual open right now looking at that procedure. I'll do the easy stuff first and go to the harder stuff progressively. It wasn't a "first run" issue per se as it has been run probably 6-8 times for different reasons. I did a full power run up the other day to check static rpm (~2150, which Catto says is the target for the prop I have) and #4 was the hottest cylinder. Something happened in our taxi test this evening to change that.

Weasel · #5 10-27-2016, 07:28 PM

I had a dead cyl at idle. Was hard to see but micro piece of something yellow in the fuel divider.

For reference the slot is ~0.003"

lr172 · #6 10-27-2016, 08:36 PM

I am with weasel. Your symptoms point to a problem condition only at idle and intermittent. Flow divider is high on the list for that symptom, especially with newly installed fuel delivery components (a great source for debris)

Larry

Snowflake · #7 10-27-2016, 08:53 PM

Maybe something even more basic... Check that the CHT and EGT probes are properly connected to that cylinder.

tim2542 · #8 10-27-2016, 10:20 PM

Good advice so far, but I'd add a quick test: pull the prop thru 2 revolutions and make sure you're getting a good "squeeze" or compression out of all 4 and you don't have a dead hole from FOD in the engine or worse.
If any doubt do a leak down test.
Tim Andres

Mark Dickens · #9 10-28-2016, 04:45 AM

All great advice and will do today! I'll report back!

Mark Dickens · #10 10-28-2016, 02:24 PM

Turned out to be some crud in the injector nozzle. I pulled the #4 injector and cleaned it with some acetone. There were two tiny bit of crud. One looked like it could be a tiny bit of sealant and the other was a tiny black fiber of some sort. Anyway, I put all back together and ran it up. All cylinders normal now. Thanks again for the advice! I'm very relieved it was a simple solution.