IO-540 Morning Sickenss or ?

I am having rough starts on a Lycoming IO-540. sometimes it is a real bear to start and sounds like it isn't running on all cylinders. Once it gets into the higher (1500 rpm) range it seems to smooth out. The compression has always been good (78/80) and is run a lot every month. After cleaning the injector nozzles it seems to run better but still not how it should. One opinion offered was that it is the fuel control unit but nothing to support why. I really hate to throw a new control unit at an unknown. Another odd quirk is that when leaning in cruise in the higher altitudes (7-9,000 or so) the fuel flow will show down to about 0 on the manual fuel flow indicator.

Any ideas?

What kind of problems would a faulty fuel control unit offer?

What would problematic fuel divider act like? Is it possible to have "morning sickness" and always have great compression on the cylinders.

Most times the compression tests are done cold and the engine has about 800 hrs. on it. It is generally run to about 60 hrs. per month and the oil is changed at 50 hr. intervals.

I had a similar morning sickness issue with a T206H. Startups were easy but it would idle rough and sometimes sputter during the run-up prop cycle. The clue was that it only happened on the first run-up of the day and would not occur when the engine was already warm. Symptoms would also diminish if I let the oil temp get above 120 before the run-up. I have recently upgraded systems to include data logging which will tell the real story, but in my case an oil change and running a bit leaner (hotter) seems to have cleared up some of the crud in the valve guides.

Hope this helps but in this case the problem appeared to be running too rich a mixture at extended low to mid power settings. Two other pilots and I were running a best power setting when we should have been running the recommended setting halfway between best power and best economy.

Try looking at EGTs during the rough running period to attempt to isolate a single cylinder issue.

Could be a sticking valve, a bad Mag, or a bad/failing plug.

As to the fuel Servo, there is a Lycoming mnadatory SB on certain model fuel servos which might have a faulty fuel diaphram. Not sure exactly what the problem it causes but you might have the symptoms. Anyway here's the link to the SB which will tell you if your servo is affected.

http://www.lycoming.com/support/publications/service-bulletins/pdfs/SB596.pdf

I forgot to mention that at low idle rpms regardless warm or colder it always seems like it has a slight miss.

I have been looking into the mag. The left mag drops about 50 more than the right but it is still within specs both sides. There is also the possibility of an impulse coupling problem as the one on it is riveted but I don't think that would cause any problems after the initially start and run up.

We check the plugs routinely every 100 hrs or so to clean and test on the bench but I may just check them out again. I am leaning toward the valves. We have also replaced 2 of the muffler packs within the last 100 hrs. and I am thinking the baffling on the only one we didn't change might be part of the problem. Lots to figure out. I am looking into the fuel servo issue now.

I also don't have an EGT monitor other than a single reading. I may try the cayon method or just a handheld infared thermometer to see if any of the cylinders are hotter or cooler than others.

Without an engine monitor and knowing what you are looking at, you are shooting in the breeze. Sure you will eventually track it down but it takes longer, more frustating and costs you heaps.

These little boxes along with the correct knowledge and understanding are hard to beat.

First of all if it is a relatively late moderl engine it should not be "morning sickness", so lets go through the simple things first.

Plugs. These MUST be checked every 50 hours. Sure there is no rule about it but the facts are despite anecdotal comments to the contrary gapping and resistance checking every 50 is how to kep them optimal. So 0.016-0.018" for gap and sub 5000 ohms resistance. This will have a large impact on your performance all all powers especially LOP and on the ground at low powers and cold.

Next point, over priming? This along with the gunk that settles in the FCU on the diaphragm changes the weight of the diaphragm and every 500 hours this is worth a service. Not an FCU change.

Ground ops. Do you start it and shove the mixture all the way in and leave it there? Along with weakening plugs this will do it too. Stop doing that if you are. During start I never actually get to full rich and I would barely get to much past half way, then I am leaning back out to the point where RPM peaks and then leave it there, only increasing mixture for just enough fuel to do a run up, and then back aggressively lean, until take off.

Magneto's......how old? and are they timed correctly....and I mean are you 150% sure. Do not trust the local A&P, are you sure.

A read of the stickied Deakin articles in this forum are worth reading also.

PM me if you would like, although Walter Atkinson John Deakin Andrew Denyer and myself are teaching an APS class this weekend so it may take a while to respond.

All the best!

Recently I had a plug show a resistance change from 0.95k ohms to 395k ohms (yes 395000 ohms) over an operating period of just 42hours. Remarkably the symptoms were an initial misfire on a mag check but cleared and ran fine during the trip home.
The thing was I noted which cylinder and which mag gave the drop in EGT so knew exactly which plug to replace. The engine no longer ran just fine, it's youthful sweetness returned...

A low rpm miss could be bad intake gasket(s) look closely at your intake tubes just below the clamp flanges for fuel stains.

ohhhhhh yeah

Lycoming intake leakes are not unusual.

250 hours seems to be a good time to have an extra thorough check.

Not sure why I say that

o-540 miss on startup

Had a similar problem that took some time to track down on a 182RG with an O-540. Eventually after all kinds of things including a cylinder overhaul because everyone thought it was morning sickness, it turned out to be a lifter pump up problem. The lifter internals can be replaced without cracking the case, it's a multi-piece affair.

It was holding the exhaust valve open and the cylinder wouldn't fire.