Just Cant Stop (even at full lean!)
 

This is pertaining to an IO360-A1A injected engine with the RSA fuel servo.

I think Gremlins broke into my hangar. I just performed a routine oil and filter change after installing silicon rocker cover gaskets and a new oil quick drain. I touched nothing else. Before re-installing the cowl I ran the engine and allowed the oil to heat up in order to check for oil leaks. After reaching 170 degrees, I pulled throttle to idle and mixture to full lean to stop the engine. The engine wouldn't stop! It just kept on purring like a kitten. No real roughness, etc. Without giving it a lot of thought, I just switched the magnetos off in order to kill the engine. My first thought was that the lean cable came loose somewhere and lost adjustment.

I checked the linkages along with the local IA. Everything looks good. When lean is pulled, the lever on the fuel servo goes all the way to the stop. A fair amount of fuel (more than usual) drained out of the sniffle valve from the sump. It had to be a fluke! Went to restart engine. It was very hard to start (which is unusual for my experience with this engine. Remember that I killed it by grounding the magnetos so fuel was still going into the cylinders since I cant get shutoff at full lean). Once started, and smoothed out, I pulled lean and saw EGTs go up. I then pulled full lean and it kept right on running. I killed the engine this time by shutting the fuel off.

I had AirFlow Performance Overhaul my servo and basically replaced the full injection system with new parts and lines, restrictors, etc. back at the start of the year.

Am I missing anything here or is this a call to Airflow to troubleshoot? I am not aware of any additional adjustments for Idle shutdown other than making sure the lean lever on the fuel servo goes all the way against the stop.

Your input is appreciated!

Ben

Sounds like a servo problem, a call to Airflow for an RMA is probably your next step. Is there a finger filter at the fuel inlet? Could be worth checking that first. Could the idle mixture lean/rich adjustment turnbuckle have moved?

There is a finger filter in the fuel inlet side of the servo. I?m not sure I understand how that would affect the idle cutoff on the engine. The turnbuckle is all new from Airflow and has the spring catch in the star wheel. To my understanding, that only affects idle mixture. Is it possible it could be set too rich to allow proper cutoff? We have been having 105 degree days since the last part of May and better than 6000 feet density altitudes.

The AFP servos that I am familiar with rely on a purge valve for fuel and engine shut off. Leaning does not completely shut off fuel flow and may or may not shut down the engine.

Erich

The idle mixture (star wheel) does not affect ICO (idle cut off) using the mixture control. The mixture control valve is upstream of the idle valve and should override any idle adjustments.

To test the ICO, disconnect the outlet from the servo and place this line into a container. Move the mixture control to ICO, then engage the boost pump and see how much fuel you get, if any, out of the outlet line. The maximum allowable is 5cc/minute, about a slow drip, any more and you may not get engine shut down.

The old style, Brass valve can be lapped to get a better seal. The new style, anodized Aluminum valves should not require this.

The purge valve is optional on the FM-150 but required (I think) on the FM-200 and larger servos.

This could be a stuck flow divider or a servo problem but I would suspect the latter. A call to Don will get you on the path to resolution.