Rough idle with aux pump on

Dear community!

Situation:
When my engine is running (1000 rpm) and i switch on my auxiliary fuel pump, rpm decreases, engine running very rough, dark exhaust gas, fuel flow increase.

Conclusion:
Mixture gets way over rich!

Solutions:
...................


The whole story:
I recently did the first engine run. Went perfectly except the thing mentioned above.
Engine is a ECi Titan IOX-360 with dual P-Mag. It starts perfectly, runs smooth as silk through all RPM range. Fuelflow and pressure are all good.
I have an Airmotiveengeneering (AE) fuel injection system that came with the engine.
Fuelflow tests were all good.
Aux pump on, engine not running, mixyure rich, fuelflow at the FUELPUMP and VAPOR SEPARATOR ASSEMBLY was 170 Ltr/hr or 37,4 gal/hr.

Aux pump on, engine not running, mixture rich, throttle wide open, fuel pump at the spider (AE fuel manifold valve assembly) was 84 Ltr/hr or 18,5 gal/hr.

After the first engine run and the issue with the rough idle i repeated the tests with the same results.
I added another test.

Aux pump on, engine not running, mixture cut off, .....BUT......
fuelflow at the spider was 12 Ltr/ hr or 2,6 gal/hr !!

That seemed strange to me!

Of course, aux pump off, no flow at all.

During the engine runs the engine quit immediately when mixture was pulled to cut off (aux pump not running).

I figure that the aux fuel pump makes so much pressure to force fuel through no matter what!

Question:
Anyone encountered the same thing?
Anyone have advice for me how to deal with it?

What is fuel pressure at idle, aux off? Aux on? Should be a few PSI different but not a big increase.
Did you confirm Mixture control cable adjustment for Lean Mixture cut off is at it's full off stop?
Did you set the Idle mixture adjustment on the servo linkage?
Did you set idle speed? or did you get it to idle below 700rpm?
Idle cut-off testing, aux pump off, at idle, and you gradually pull back on the mixture knob, do you get a 50 rpm rise before engine dies?

With engine off testing, and getting fuel flow numbers like that, I hope you have a drain hole to get rid of the fuel puddle at the servo entrance!

Good luck with the testing/adjusting.

I don't know anything about that FI unit, but a bendix should handle pretty high fuel pressures without issue. Have you confirmed fuel pressure with the pump on? Given it is a new unit, possibly the ball in the relief circuit is sticking, causing high pressures. Those pumps can produce well over 100 psi at low flow volumes, without an operating relief.

Larry

Problem most probably solved

Today i ran the engine again to check all numbers like fuelflow and fuelpressure.
All were in limits and the engine was smooth as it can be.

I re-read the installation and operating manual and stumbled over two paragraphs.

First one differentiates between high pressure (22-28 psi) and low pressure (5-8 psi) auxiliary / boost fuel pump.
Second one defines the operating procedures. High pressure pump is only used to purge and prime the engine prior start and in case of mechanical pump failure (?emergency? that is). EXCESSIVE OPERATION WILL FLOOD THE ENGINE.
The low pressure pump MAY BE OPERATED CONTINIOUSLY DURING TAKE OFF, HIGH ALTITUDE OPERATIONS AND LANDING.

I consider the behaviour of my system as completely normal!
I also consider the low pressure fuel pump as optional.

Case closed?

ECI had an option for that system way back when, same basic design that a continental has. Sounds normal.

Thanks Walt, it is always helpfull when someone supports your way of thinking.

It is in fact an ECi System and i ordered it “way back then”.

Only thing i do not understand is this:
I do have a vapor return line with the same diameter than the supply line.
The flow capacity of both lines should be equal.
Why is (mixture) “cut off” still letting fuel flow further up front?
Why isn’t all the fuel from the aux boost pump going through the vapor return line back to the tank it comes from?

I would suggest you do some reading up on the TCM system to get a better understanding of your systems operation. I'm no expert on TCI systems but I believe with your fuel pump running in 'HI' (you don't have a 'Low') you are simply overpowering the normal mixture idle cut-off.
Typical idle unmetered fuel pressure for those systems is somewhere around 6-7 PSI (they use a positive displacement pump so output pressure varies with RPM).