Fuel injection problem

[aaronk25]

Been having a issue since overhaul, that I attributed to low idle as the engine has killed a couple times on the runway after landing.

The fuel servo was overhauled a couple months ago at D&G supply in MI, and that's when the problems started.

I pulled the Edm-800 data yesterday and realized that both of my engine stalls on the runway were due not to low idle but to the fuel flow not reducing enough. It was stuck at 4gph, and severely flooded the engine.

When I descended after the long flight home from the mooney summit, which was a high speed, cruise power decent near VNE, to stay ahead of jet traffic, the fuel flow got stuck at 10.8gph when trying to reduce power power below 17" the engine stuttered violently then went cold, until I moved the mixture knob to idle cut off then back to normal setting.

As I understand it the fuel servo has impact tubes that measure high pressure air entering the fuel servo air against low pressure air in the servo to act as a "auto mixture" adjustment and part of this is a needle valve and diaphram.

My best guess is that this valve is hanging up, intermittently at whatever setting was used for a period of time during the decent which is why it hangs up at 4gph on normal approaches and higher values on faster approaches.

It also didn't give me enough fuel on a restart at a fuel stop on the way home which lead to a rough running taxi.

The only thing that gets the fuel servo working properly is if I move the mixture knob to idle cut off then back to rich.

I think doing this seems to get the needle/diaphram moving again.

I also noted fuel flow on take off at 16.5gph instead of the normal 18.5gph, pre-overhaul.

We removed the servo and D&G received it and said it bench tested fine and it was flowing 18.5gph for them.

I asked them to disassemble it as there is obviously something wrong and needs to be corrected. I was told that for $400 they would re-do the overhaul, but that since it functioned fine on the bench they weren't going to open it up, unless I paid them. They did note the low fuel pressure was at bottom of the lower end of the spec so they adjusted that.

I told them I didn't want to pay them again since i just paid them to overhaul it.

Does anyone have any idea if what the issue could be? Is my hypothesis close?

D&G seem to think the flow divider is the cuprite (of which they did not overhaul) but I don't understand how that could keep my fuel flow at 10.8gph when the throttle is closed...

We're gonna put it back on and try it but im guessing the problem is not solved.

Help....thoughts....recommendations for a different fuel servo shop?

[N201MKTurbo]

Have you adjusted the throttle stop and the idle mixture? It usually takes about 1/2 hour and about 5 engine runs to get it right. It has always cured the symptoms you describe.

[aaronk25]

Adjust the mixture so at fuel rich and 800rpm it is using 1.8gph, to which I lean to 1.3gph for steady state idle or during taxi enrichen a bit for power to go up hills. I think the idle mixture is dead on. The throttle arm is hitting the idle stop adjustment and idling at 800ish. WOT is OPENING all the way and hitting the stop too.

Literally the engine died on down wind on last landing due to fuel flow not reducing below 10.8gph. The engine just couldn't digest 10.8gph at reducing MP below 20"....as soon as I went to idle cut off and back to rich the fuel flow dropped to around 4gph, right where it should have been given I was commanding 15" of MP...

What could cause this excessive rich condition?

[Mike A]

When I got my 231 it had an engine-driven fuel pump that was freshly overhauled by D&G.  It ended up being the source of a lot of frustration for my first 6 months of ownership.

 

My engine had issues starting and operating on just the engine driven fuel pump after a few flights.  The mechanics went through the fuel system over and over again and the pump always returned as the issue.  This included putting the pump from a Cirrus they had in the shop on and running up the engine.  

 

I called D&G and sent the pump back for testing. They told me the same thing; that it operated fine on their bench.  They sent it back to me and it still did not operate correctly on the engine.  After some arguments, they agreed to send me a second unit to try.  Same result.

 

I stopped by TCM's booth at SnF to ask about the issue and they said they don't provide overhaul specs of their accessories to outside vendors.  I would suspect that Lycoming is similar.  I purchased a re-man pump from TCM and it worked perfectly the first time.  After some more discussions with D&G, they agreed to refund the purchase price that was paid by the previous owner and send me back a core in return for the two pumps they had sent me.

[KSMooniac]

I would agree that D&G is not doing something completely or correctly.  Suggest you try calling Aircraft Carburetor and Injection Services of Texas, LLC (214-358-2377) and chat with them.  That is Maxwell's preferred shop for the Bendix system and they just did mine plus my spare system.  I haven't run it yet unfortunately, so I cannot give you a good PIREP.

[Guest]

Send it back to Precision Airmotive in Washington, they're the manufacturer and not really very expensive.

Clarence

[aaronk25]

Send it back to Precision Airmotive in Washington, they're the manufacturer and not really very expensive.

Clarence

I would love to but they refuse to repair any servo that D&G supply overhauled because they don't buy "factory parts" from them.

The only option is to buy one of their servo for $1740 (my mechanics cost).

D&G supply is shipping me anther fuel servo on Monday to install. It appears they are taking the right steps and standing behind their work.

I am getting annoyed with the out of pocket cost of R&R the servo and shipping. If this exchanged servo fixes the issue, I will be out of pocket $850 r&r x 2 and shipping.

[RobertGary1]

When I had my fuel servo flood and kill my engine on climb out I sent it for overhaul. Came back and it did the same. Sometimes they don’t get it the first time. 

-Robert 

[Igor_U]

4 hours ago, RobertGary1 said:

When I had my fuel servo flood and kill my engine on climb out I sent it for overhaul. Came back and it did the same. Sometimes they don’t get it the first time. 

-Robert 

How long would you say for removal and replacement? Mu fuel flow on takeoff is around 16gph (seems to be somewhat higher before) and might need bench adjustment or OH...

 

[aaronk25]

So what ended up being the problem? Did Russ at D&G make it right.

The replacement fuel servo did work. The cost to r and r the first and install the 2nd one was on me, however in hindsight I could have done a better job in the preplaning and would have known this.


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[Shadrach]

29 minutes ago, nosky2high said:

Thanks for the update, the way this thread was left it appears that D&G was the culprit.

 I’m not so sure about that. I see nothing here that shows that there was any attempt to troubleshoot the original installation.

Edited December 4, 2018 by Shadrach

[RobertGary1]

1 hour ago, Igor_U said:

How long would you say for removal and replacement? Mu fuel flow on takeoff is around 16gph (seems to be somewhat higher before) and might need bench adjustment or OH...

 

What model engine? Pull power climb at low density altitude is 16-18gal/hr in IO-360. 

-Robert 

[Igor_U]

15 hours ago, RobertGary1 said:

What model engine? Pull power climb at low density altitude is 16-18gal/hr in IO-360. 

-Robert 

IO360-a1A in my '67 F. FF is 16.X gph at my home field 570' (it gets in high 15.X after few minutes of climb) and I remember being somewhat higher...

From what I see here, that's on lower end for our engines.