Erratic Fuel Flow at LOP

John Collier · #1 11-21-2014, 04:33 PM

Seeking advice/experience with fluctuating fuel flow when operating LOP. I balanced my nozzles a couple of years ago and had good success operating LOP. Recently, my fuel flow is indicating anywhere from 8 gph to 6 gph after I set the mixture. The EGT is unstable and I can tell the engine is not running smoothly...my guess is because the fuel flow is indeed inconsistent.

I'm planning on cleaning the nozzles and looking at the divider.

My typical cruise altitude is 8500 to 12500.

The OAT has cooled off considerably in the Southeast...I understand a higher fuel flow would be required based on a lower density altitude...but would that contribute to this problem?

What am I missing?

Geico266 · #2 11-21-2014, 07:14 PM

Can you describe your system?

John Collier · #3 11-21-2014, 08:19 PM

Mattituck IO-360
Dual PMags (timed correctly & monitored with EICommander)
Precision FI (balanced nozzles from Airflow)
Dynon Skyview

rvmills · #4 11-22-2014, 01:53 AM

John,

If you have individual EGT readouts, are you currently seeing one or more cylinders going LOP early? I've had two cylinders that leaned before the rest, and once those cylinders get too lean, I could hear and feel the roughness, and noted the FF drop more rapidly per twist (or partial twist) of the mixture knob. Not sure if that is what you are seeing, but injector cleaning seems like a good troubleshooting step. Good luck!

Cheers,
Bob

John Collier · #5 11-22-2014, 05:49 AM

I do have EGTs for each cylinder. When I first balanced the nozzles the EGTs peaked within 20 degrees across the cylinders. Now, I can't get consistent peaks. One attempt will have a 30 degree spread...another a 10 degree...another a 50.

My real question is why I don't have consistency on fuel flow. The EGTs don't stay at a solid reading...cylinder EGTs are +/- 20 degrees as the fuel flow fluctuates. My fuel flow has varied up to 2 gph after setting the mixture for LOP.

I believe if I could get the fuel flow to stabilize after I set the mixture...my LOP operation would be fine.

Also, the fuel flow is stable ROP and the engine runs great.

Maybe a higher being is trying to tell me to stop running LOP

AlexPeterson · #6 11-22-2014, 06:19 AM

John, perhaps you have a fuel flow indication problem that shows up at those flow rates. Others (Pete - what was your experience?) have found that the little window inside the transducer gets clouded or otherwise obscured, giving erratic readings. The roughness may just be that you are running more lean than you believe. If the 2 gph variation were real, that is a lot, and enough to take you from LOP to ROP.

Just a thought.

John Collier · #7 11-22-2014, 06:53 AM

"If the 2 gph variation were real, that is a lot, and enough to take you from LOP to ROP."

It does take me from LOP to ROP....or I have to lean so much that the engine gets very rough. The 2 gph was the extreme i've seen since the OAT cooled off...but 1 gph fluctuation is common.

I'd thought about the transducer being inaccurate...but I'm using the Dynon's LOP feature and watching the EGTs peak. At peak to LOP...that is when the fuel flow gets weird.

RV10inOz · #8 11-22-2014, 06:58 AM

Check for intake leaks first.

John Collier · #9 11-22-2014, 07:33 AM

Thanks Dave.

The manifold will be my first check. Then I'm thinking I need to look at the size of my nozzles as I might be bringing the fuel divider into the equation at low fuel flows. That makes sense in my mind...as the problem only shows itself at approx 7gph fuel flow.

thanks!

Pmerems · #10 11-22-2014, 07:55 AM

John,

I posted a week or so ago about an erratic flow rate at LOP. I had never an issue with my D180 install but I upgraded to Skyview and just completed a long cross country and had fuel flow swings +/-.3 without any noticable engine performance changes.

My fuel usage was off as well. I still have not done investigation to do but it only occurred at LOP @9.5k but did settle down. My fuel totalizer was accurate with the D180 system but apparently not was the Skyview.

250+ hours on my bird and loving it. I am glad you kept your RV8. I have pictures of your bird off my wing hanging in my office. That camo paint scheme attracts a lot of attention.

Shotgun moved to CO flying 16's with the COANG. I am helping another C17/T6 pilot with his 7. Hope to get it flying at the end of January. He just accepted an AZANG KC135 job in Phx. I must be scaring all the Arizona AF RV guys away.