Last week after starting my PA24-250, I felt it was running a bit rough at idle and checked the JPI. #2 EGT was off-the-scale cold, while other EGTs were appropriately warm. I slowly increased rpm and at around 1200 rpm #2 began to register some temp but was still much lower than the others. I tried leaning and switching mags but it made no difference. Continuing to increase rpm up to about 1800 brought #2 up to normal and even with the others and operation felt smooth, but reducing rpm back to idle caused #2 to plummet off the scale again. At that point I was concerned about a possible stuck valve so shut it down.

Downloading the JPI data confirmed the EGT did what it appeared to be doing, and that during this 4 minute engine run the #2 CHT rose less and much more slowly than the others. Since then my mechanic has checked #2 compression (78/80), verified the valves appear to moving normally, borescoped the cylinder and valves, pulled the valve cover and performed the Lycoming Mandatory Service Bulletin 388C procedures, changed the oil and filter and checked the filter element and oil screen (oil analysis results still pending), with no abnormalities found. The engine has about 300 hrs since Mattituck major, Oil is Aeroshell 80 Plus with Camguard and had 25 hours on it, OAT at the time was 30F but the airplane was just pulled out of a heated hangar where it is always kept at about 60F. I haven't had the opportunity to start it up again, but am concerned that no explanation for the #2 anomaly could be found. My IA consulted with some guru in Tulsa who said stuck valves are more likely to occur when the engine is hot, not when relatively cold like this one, but...?? Is this the typical "Lycoming morning sickness" of a sticking valve (with no evidence of sticking now) or something else?

Have any of you seen this sort of thing or know what it would be due to? Any help or advice will be appreciated.
John Johnson

Hi John:

Sounds to me that cylinder is not getting its fair share of fuel from the carb or proper spark. I suspect your AI has checked the intake tubes for tightness so if all intake leaks are ruled out
and all the other cylinders are relatively even.... by even I mean not cold and not hot EGTs, carb engines are not so even with idle EGTs...... My suggestion is to check out the ignition wires
and spark plugs to that cylinder. During the run up do you get an EGT rise when testing both mags on the number 2 cylinder?

Good luck,
Gary

Gary, the EGT rose with increasing rpm on left, right, and both mags, so mag selection made no difference in EGTs. It appeared to be related to rpm more than anything related to spark distribution. Seems to me if it were a spark generation problem it would have to be affecting both mags on same cylinder simultaneously, or both #2 plug wires or both #2 plugs - any of which would seem improbable in those scenarios. Also, I can't see where engine rpm should affect those issues.
John

John: You are right, doesn't sound like a spark problem if you are getting the Egt rise from both mags during runnup.
Now that you have ruled out the compression and have no issues with valves... I would go back to looking for a manifold leak to that
clyinder. The lycoming trouble shooting manual points out the various places to look, including the following:
3. Induction air leak at one of the
following locations:
a. Hoses and hose clamps.
b. Cracked intake pipes.
c. Bad gaskets.
d. Loose flange bolts.
e. Loose plugs in intake port of
cylinders.
f. Fuel drain valve not seating
properly.
3. Check previously mentioned
locations and tighten or replace as
necessary.
3. Solution is self-explanatory.
After these are checked out.. my opinion is to go flying at cruise power for 45 mins or so and see if that clears up the problem.

For general info here is the link for the manual. http://www.lycoming.textron.com/support ... -Guide.pdf

Hope it helps,
Gary

Thanks a lot, Gary! I hadn't seen that Trouble Shooting Guide, so that should prove very helpful, even for future porblems. I'll check those issues out.
John

Your Welcome John.I hope you can pinpoint the problem without pulling your hair out.
Let us know what you find.

Gary

Gary, I flew from Springfield MO to Aurora IL this AM, 2.5 hr en route, with absolutely no indication of trouble. I'm just now getting ready to return to SW MO, and if this flight's as uneventful, I guess the problem will likely just go undiagnosed. Maybe Pat was right about a lead ball or some such causing transient valvle sticking. Again, thank you and everyone else for all the help!

John