Ran great until it didn't

Ran great until it didn't - cold EGT and CHT at low RPMs

I recently finished my -7A and started flying, which has been enormous fun. Lycoming O-360-A4M out of a 2002 Piper Archer that was wind damaged and had 1100 hours since OH in Aug 2014 (flight school plane).

After the 3rd flight, the EGT and CHT would drop off on the #4 cylinder below about 1400 RPM. We went through the following to get to the root cause:

* Induction leak?
-- Replaced induction tube gasket at the #4 cylinder. Tightened all clamps and torqued all bolts. No help.
* Both plugs fouled?
-- Pulled plugs, cleaned, gapped, checked resistance. All good. No help.
* Mag problem?
-- Mag check at 1700 RPM seemed normal.
* Worn cam lobe?
* No issues with #3 cylinder, which shares the same intake lobe.
* Valve sticking?
-- Borescope showed no signs of issues with the valve movement or bore.
* Idle mixture too lean?
-- Richened idle mixture at AFP servo. Improved idle but not the issue.
* Compression issue?
-- Compression checked was 72/80 (1100 hrs on this cylinder)
* Not enough fuel getting to the cylinder?
-- Blew out the injector line. No help.
-- Checked flow to cylinder with fuel pump on. Bingo. No fuel at idle and a dribble at full throttle, full mixture.

Swapped out the fuel divider and all was well again. Mine will go back to AFP for IRAN.

Raymo said:

After the 3rd flight, the EGT and CHT would drop off on the #4 cylinder below about 1400 RPM.
-- Checked flow to cylinder with fuel pump on. Bingo. No fuel at idle and a dribble at full throttle, full mixture.
Swapped out the fuel divider and all was well again. Mine will go back to AFP for IRAN.

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Glad you solved your problem, but from your description I infer that everything was fine above 1400 RPM, and yet you say that fuel flow was found to be only a dribble at full throttle. Am I missing something?

Erich

erich weaver said:

Glad you solved your problem, but from your description I infer that everything was fine above 1400 RPM, and yet you say that fuel flow was found to be only a dribble at full throttle. Am I missing something?

Erich

Click to expand...

It was getting enough to run lean and seemed fine (EGT and CHT on the rise) in the short test runs we did between troubleshooting steps.

Have seen one AFP fuel distributor that the same problem occur as yours. It had been in use for 8 years or so, the fittings going to the lines or the fuel pressure, (don't remember which), had dissimilar metals corrosion and plugged 2 of the fittings going to the injectors. Simply cleaned the crud out of the inside of the distributor hsg and changed to a different material on the fittings.

Raymos issue was puzzleing. At altitude things seemed normal and normal temps, especially the first couple of hours of flight. Then all of a sudden it literally wouldnt run at idle, and above that the temps would stabilize, but it certainly seemed to be down on power. Ray borrowed another AFP flow divider and the engine perked right up. I'm sure Don and Kyle will find something wrong.

Good head scratching troubleshooting by Raymo and Dennis.
Tom