DaleB
Well Known Member
It seems that any time I get over 7500 MSL, I get a "FUEL FLOW HIGH" alarm. It's particularly annoying because it comes and goes, meaning I silence it and a few seconds later it's back again. Over and over, during climb and level cruise, with the D180 erratically indicating anywhere from 8 or 9 to well over 10 GPH fuel flow. Obviously there is not really 10-plus GPH flow. No gas smell in the cockpit, no evidence of overflow, no flames or explosions.
It happens with the unleaded, ethanol-free MOGAS that I normally run. It happens with Swift 94UL. Today it happened after I'd just added 15 gallons of 100LL to the last remaining 5 gallons of 94UL. It's happened in winter with OAT well below freezing, and today with OAT at 8500 MSL of around 10 C. The only constant seems to be, 7500 MSL or higher. I haven't tried drastically reducing throttle, but I'm typically running 5200 - 5400 RPM at most.
If I pull the fuel pump fuse, the alarm immediately stops, fuel flow indications return to a normal value of 5.5-6.5 GPH, depending on throttle, and all's well. When I put the fuse back in, it may go back to the constant bouncing alarm -- or on rare occasions not, although the indicated fuel flow always goes up a little (no change in EGT or CHT, just higher fuel flow indication). If I descend to 6500, all is well with no alarms. Fuel pressure stays within the green range at all times... on the low end with no boost pump, on the higher end with it on but always in the green. CHT and EGT don't vary with the fuse in or out.
My indicated fuel use from the D180 is reasonably close to actual usage after most flights. The "k" factor could use a little tweaking for better accuracy, but it's not THAT far off. And if I stay below 7500 MSL, I never see the fuel flow alarm.
Ideas, folks? I'm just about out of them. Have not run this past Van's yet, but will in a week or so if a root cause and/or solution does not become apparent.
It happens with the unleaded, ethanol-free MOGAS that I normally run. It happens with Swift 94UL. Today it happened after I'd just added 15 gallons of 100LL to the last remaining 5 gallons of 94UL. It's happened in winter with OAT well below freezing, and today with OAT at 8500 MSL of around 10 C. The only constant seems to be, 7500 MSL or higher. I haven't tried drastically reducing throttle, but I'm typically running 5200 - 5400 RPM at most.
If I pull the fuel pump fuse, the alarm immediately stops, fuel flow indications return to a normal value of 5.5-6.5 GPH, depending on throttle, and all's well. When I put the fuse back in, it may go back to the constant bouncing alarm -- or on rare occasions not, although the indicated fuel flow always goes up a little (no change in EGT or CHT, just higher fuel flow indication). If I descend to 6500, all is well with no alarms. Fuel pressure stays within the green range at all times... on the low end with no boost pump, on the higher end with it on but always in the green. CHT and EGT don't vary with the fuse in or out.
My indicated fuel use from the D180 is reasonably close to actual usage after most flights. The "k" factor could use a little tweaking for better accuracy, but it's not THAT far off. And if I stay below 7500 MSL, I never see the fuel flow alarm.
Ideas, folks? I'm just about out of them. Have not run this past Van's yet, but will in a week or so if a root cause and/or solution does not become apparent.