Spider

[md11flyer]

Hello:

After an extensive idle period while many upgrades were done, panel, jpi engine monitors, rams yoke control columns, interior, annual etc,
I have a diff of about 500 degrees at idle with number 4 being cold. When the engine is run up to 2200 rpm the egt climbs up to match the others. Then after a few seconds
the egt rises further about 200 degrees above the others. The compression on that cylinder 2 weeks ago was 79/ 80... 2 cylinders were mid 70's, and 1 at 68/80. Compression was taken
after engine was sitting for about 5 months. Pulling prop through confirms there are no dead clyinders... all about equal compressions..(by feel)
A mag check confirms that both spark plugs are firing (slight egt rise on both plugs when doing the check).
I also notice that at idle the manifold press of that engine is about 2 or 3 inches differrent from the left engine.
A visual inspection and retorquing the clamps on the manifold tubes indicates they were tight.
A check of the manifold check valves shows they are working properly. (can suck air from the hose and blowing into the hose you hear the tell tale click and the valves are shut)
The removal of all injectors and servo fuel screen.. all squeaky clean.. cleaned the injectors with MEK and fuel screen with avgas and blown dry.
Never have water in the fuel...stored in hangar and sumped regularly
Fuel selector sumps also always squeaky clean when taken off for cleaning.
During full power run up both engines are matched regarding fuel flow and manifold press. I was light so I couldn't prolong the run up beyond a couple of seconds. ( tires were sliding)

On return to the hangar with engines at idle the egt dropped off again on number 4 cylinder and the occasional back fire was heard.
My guess is that even though there is no indication of contamination in the fuel system there might be something going on with the spider.. maybe rust partially blocking the
port to number 4 cylinder..( Low fuel flow at idle and at higher power settings higher EGT..indicating leaner mixture.)

My first question is, can you open up the spider in the field and check for contamination? Or does it have to go to an overhaul shop?
Second Question is, Has anybody had this problem as well?

Any thoughts and suggestion are appreciated.

PS Now that I think about it this problem has probably been happening for some time now... always did have a rough idle on this bird
and now with the JPI I now know where the problem lies.

Gary

[skipsouthernsky]

Dear Gary,

I am assuming that what you are calling the spider is actually the flow divider. If so, I don't know from your information if that part of your fuel injection system is what is causing the symptoms or not. From your description, it is a distinct possibility though. Yes, it is possible to take the flow divider apart and clean it out and inspect it inside, although to the best of my knowledge, not FAA approved. The inside consists mostly of a spring and a rubber diaphram. The cap comes off with just a few screws. On the other hand, Aircraft Spruce sells a generic (approved) overhauled flow divider for $190. In this case you have to take a picture of the one you are removing and keep all the plugs and such (mounting brackets) so that they can be installed in all the same places on the overhauled flow divider. It is really pretty simple. There is some core charge which is most likely to be refunded upon receipt of your old core.

You might want to check on how long it has been since the last flow divider overhaul. Longer than twenty years?. Maybe the rubber diaphram is deteriorating. At any rate, not a really expensive item.

Sincerely,
Skip Dykema

[md11flyer]

Thanks for the reply Skip.
Yep a little loose on the terms. I was indeed referring to the flow divider. When I get back to the hangar I will
just swap the flow divider from the left engine and if that cures the problem will pick up an overhauled one from Spruce to replace the defective unit.

Gary

[md11flyer]

Follow up to the problem.

It was indeed a faulty flow divider. I swapped the 2 flow dividers and the cold cylinder and associated rough running, and uneven manifold pressure
also swapped to the otherside. Another advantage to having 2 engines!
Because of the inexpensive replacement overhauled unit I didn't bother taking the faulty flow divider apart to see what the problem was. My guess is a small obstruction in
the internal of the divider.

So there it is for anybody that has this problem in the future after cleaning the injectors and lines check out the flow divider.

Cheers,
Gary

[N3322G]

Thanks for posting the problem resolution so we can all learn. So far, our twin's issues like this have always been corrected with injector cleaning - wouldn't have thought of the flow divider without your experience.

[John Wasserburger]

Hi Gary,

I had a similar problem with the flow divider due to the aircraft sitting for a prolonged period of time. I had to take it apart several times and blow the spider lines out with air. This would work for awhile, then I would have to do it again after about 10 hours. After the third time, everything worked fine and I am about 100 hours flying with no issues.

John W.