Injector problems

[Kevin Weidner]

We just got through with replacing all the rubber lines on our Twin Comanche, which I fabricated myself with new hose and the reusable fittings. Apparently there is a piece of dirt or rubber somewhere that I did not get cleaned out of the line well enough, because one engine is running very rough on 1 or 2 cylinders with a high fuel flow indication.

We cleaned all 4 injectors and checked the flow into some small paper cups out of the individual lines with them disconnected from the injectors. There seems to be slightly less flow on the #1 cylinder, but it happens to be the highest line, which might constitute less flow without the injectors hooked up for the resistance. We took that line loose at the flow divider and blew it backwards.

Is it possible that the flow divider is partially clogged causing this situation? Can you take the supply line loose and blow backwards through it?

I was hoping someone could point me in the right direction from here.

Thanks in advance.

[md11flyer]

Be careful about blowing air into the flow divider. You might damage the diaphragm inside. Also you just might lodge any debris in another place inside. Just take the 4 screws out and remove the diaphragm and spring and clean the inside thoroughly. It doesn't take much to clog up the small passages inside the divider.

Good luck,
Gary

[Kevin Weidner]

I think we will take the top off and hopefully the diaphragm won't tear when we separate the pieces. Where can I get a new diaphragm if I happen to damage it when it comes apart?

[md11flyer]

Not sure where you can buy the diaphram, but if you find you need another divider, Aircraft spruce sells the dividers for a reasonable price with your old as a core allowance. Unless the unit is ancient, it shouldn't give any problems coming out.

Gary

[Zach Grant L1011jock]

Kevin,
I would bet that something is gumming up the valving in the servo, not the flow divider. This is a pretty typical symptom for a servo problem, but it doesn't explain the high FF indication as that would imply clogged injector(s). You may have other issues going on here such as corrosion in the servo, and or floating debris, and or a disentegrating flow divider diaphram. These fuel issues are maddning, and unfortunately expensive because the true culprit is often very hard to nail down. Good luck!
-Zach

[Kevin Weidner]

We took the top off the flow divider this afternoon and found several pieces of the old rubber hose in the plunger inside of the divider. We took compressed air and blew through all of the openings with all the lines disconnected and put it back together and it runs normal now. The fuel flow is still about 15.5 gph on the gauge, compared to about 14 on the left at full power, but could this just be a gauge calibration problem?

[Kevin Weidner]

We took the cover off the flow divider and found several pieces of rubber from the old hose in the little valve inside of it. After blowing it out very thoroughly from every port and re-assembling, it runs like a champ. For some reason, the right fuel flow still shows 1GPH higher on takeoff and proportionately higher on other power settings. Is it normal for these gauges to read inaccurately? It runs great and the EGT's are at the same indication when the FF's read different.

[N3322G]

Kevin,

Had the same uneven reading. Replaced the really, really old transducers and now they read the same + or - 0.1 gallon.
there may be other causes for it but that was our experience.

[Zach Grant L1011jock]

Kevin,
If you have the stock fuel flow gauges, this is not uncommon. They are simply pressure gauges calibrated for fuel flow and pick off of the flow divider. I would certainly say 1 gph is close enough for govmt. work. It wont take long to get used to the new standard of where the ff should be. Even if they are accurate, the FF varience is within the specs for the engine.
Zach