Rough engine and low EGT on #2 just after t/o. Any ideas?

[ao.frog]

Hi gang.

Today, the wifey and me loaded up the -7 for a 3-day trip to Sweden, but we didn't get far: start, runup and takeoff-roll normal but at 500', we both felt a slight vibration and I noticed the EGT on #2 was approx 650*F.
CHT on #2 where at the same level as the others: about 400*F.

I turned back towards the field and entered downwind.

The vibration got slightly worse when reducing power to about 15'MAP on downwind.
The #2 EGT continued to show beetween 600 and 650, varying slightly with power.

There where also a few pops heard, and to me they seemed to come from the exhaust system.

The pops continued during base and final, both on low powersetting (15 MAP) and idle.

After taxi inn, I tried to do a mag check but the engine sounded rough when I advanced power from idle, so I only did a quick mag check at 1500 RPM before shutting down.
The roughness where present at both mags, when tested separately, as well as on "both".

After shutdown, I pulled the cowl and checked the P-mag timing: both bang on.

Then it was time to call it a day, accept the fact that the great weather forcast for the next few days, where not to be spent flying in Sweden.

My plan is to check the compression as the next step. I'm thinking that this must have something to do with cyl 2. Maybe sticky valves?

The engine has about 41 hrs TT, I'm still using mineral oil and running it hard.

I'm certainly no engine expert so I'm wondering if anyone have some advice regarding what to check to determine the cause?

[sailvi767]

Check the easy stuff first. Carefully check the spark plug leads and plug boots. Make sure nothing is loose. Then pull the plugs and check or replace them. With a 650 degree EGT I think that cylinder had gone cold and the CHT did not have time to start dropping. If no ignition issues then check the injector for a clog. After that start getting into the harder stuff.

George

[hlangebro]

Check for induction leaks on the intake tubes, both the hose and the upper clamp

[Ralph Inkster]

Also check for broken exhaust flange, would cause low EGT & near immediate fouling of plugs.

[Neal@F14]

Originally Posted by hlangebro

Check for induction leaks on the intake tubes, both the hose and the upper clamp

...and that one of the little hex-head plugs threaded into the intake port hasn't fallen out (on the lower side of the cylinder head, where a fuel primer line would screw into if you had a primer). Had that happen on a friend's Piper Cherokee who'd just got a freshly overhauled engine installed... the engine shop forgot to tighten those plugs, the primer was only connected to two of the cylinders, and the other two cylinders had plugs. After landing we found one remaining plug only finger tight and the other plug fell out sometime during the first test flight, making a huge intake leak and it ran very rough and backfired a lot.

Also, if you happen to have one of those mechanical push-pump type fuel primers, and if it happens to be only connected to that one cylinder, make sure the primer knob is fully in and locked or else it will run super rich as it's allowed to freely suck all the fuel it can thru the primer line and pretty much kill off any power that cylinder would've been making and foul the spark plugs. Don't ask me how I learned that one

[brad walton]

I will be interested in what you find because I have had the same thing happen to my Superior IO-360 on several occasions. #2 cylinder drops to 650 degrees and it runs rough. Mine has occurred during LOP operation and once when I cut the throttle abruptly while in cruise flight. I switched the plugs with the #4 cylinder and still had it happen. No sign of intake leak. Slick mags timing is good and no obvious problem with the wiring. Mine is intermittent and usually only for 15 seconds or so. I have performed the ignition system stress test (LOP in cruise and switch off one mag, then the other) and nothing obvious on the graph to indicate a problem. Maybe the exhaust valve is hanging up?

[sailvi767]

Originally Posted by brad walton

I will be interested in what you find because I have had the same thing happen to my Superior IO-360 on several occasions. #2 cylinder drops to 650 degrees and it runs rough. Mine has occurred during LOP operation and once when I cut the throttle abruptly while in cruise flight. I switched the plugs with the #4 cylinder and still had it happen. No sign of intake leak. Slick mags timing is good and no obvious problem with the wiring. Mine is intermittent and usually only for 15 seconds or so. I have performed the ignition system stress test (LOP in cruise and switch off one mag, then the other) and nothing obvious on the graph to indicate a problem. Maybe the exhaust valve is hanging up?

I have had the same thing happen when descending LOP. What is happening is the mixture gets leaner as you descend and you reach the point where that cylinder can't ignite the fuel charge. Next time it happens richen the mixture without touching anything else and I think you will find it goes away instantly. It's normal and nothing is wrong.

[PaulR]

Sounds a little like a stuck exhaust valve to me. Had it happen on a PA28 many moons ago.

[RV10inOz]

The most likely cause is an induction leak as mentioned already. Hose clamps, sump joint or the gasket under the head.

Primer plug is another sneaky gotcha but not as common.

To get an EGT back down at 650dF you must have a very big leak otherwise the EGT would be high.

You may have a fuel nozzle blockage. And it is running so lean of peak it is almost shut down. Do not rule that out.

[Lars]

If everything else has been ruled out and the engine happens to be an older Superior 360 with roller cam, then it could be a stuck lifter (note that in this case it'll be an automotive roller lifter, not a Lycoming type with removable plunger). This happened to me, and it was not easy to diagnose. Much time spent staring at engine monitor datalogs.