Fuel Pumps 101: Dirty Fuel Is an Enemy

It was déjà vu all over again. Not two days after a reader asked if we recommended he replace the fully functional aux fuel boost pump during his Lycoming IO-360 engine swap (we weighed in saying to check with the manufacturer, but that failures are rare), the aux boost pump on our Van’s RV failed after less than a year and 100 hours in service. That got us thinking about on-condition replacements. So for clarity we asked a couple of busy shops how many pump failures they see in a given year and the answer was generally “not many.” But every mechanic warned the best thing you can do is inspect them often and keep the fuel that pumps through them clean.

How Many Pumps?

Of course that depends on the airplane. Some stone simple gravity-fed fuel systems on carbureted engines might not have any pumps, while fuel-injected models likely have both an engine-driven primary pump (usually mounted on the engine’s accessory case) and an aux boost pump. If the engine is carbureted, the electric aux pump is a backup if the engine-driven pump fails, which explains why you generally turn the pump on for takeoff and landing. It gets more complex on models with aux fuel tanks where you can move fuel around by cross-feeding tanks.

Unless the pump fails early on, shops we talked with said it’s very likely that the typical engine-driven pump on a common Lycoming IO-360 (as one of many examples) will go far beyond engine TBO, but many pumps are replaced based on time in service and per manufacturer guidelines. Preventive upkeep could be worth it—fuel pump failures can leave you stranded, especially if your engine requires one for priming during startup. The Facet electronic pump for our Rotax engine showed signs of failing during flight, creating an attention-getting burning odor followed by what we believe was high current draw, and then wild spikes in fuel flow, with a drop in fuel pressure. While troubleshooting, the pump sometimes wouldn’t run at all or ran at a much reduced output. We swapped it out with a newer version of the Facet that has a slightly higher output and noted perfect pressure, flow, and lower electrical draw.

Filtering

The other good news is that fuel pumps generally don’t require much service between swap-outs, but they can be a source of leakage and that’s a big problem. Hit the manual and learn where the fuel pumps are located in your bird. Smell fuel? Point your nose in that general direction, while looking for leaks. For years, fuel pump overhaulers and manufacturers have warned that sucking debris through a pump does it no favors for longevity. And it’s easy to mix up debris during maintenance, especially when working with old fuel tanks and aging fuel lines. Flushing the system is key.

“My shop installed a big-screen engine and fuel display, having to drain and fill the tanks several times when they struggled to get accurate readings from old sensors, and within five hours of flying, the engine-driven pump failed,” the owner of an old Mooney told us, admitting that the fuel bladders on his plane weren’t exactly new. Neither was the pump, replaced at the last engine overhaul 10 years prior.

Whether you had fuel system work done or not, an important task during annual inspection should be to check the fuel screens and filters. You don’t want debris anywhere in the fuel system, including in pumps, gascolators, carburetors, transducers, and fuel injectors. Some experimentals and LSAs have limited fuel filtration, and it might be worth installing an inline filter before the pump. If you burn unleaded pump fuel and roll your own fuel farm, make certain the fuel remains clean and fresh by storing it properly. We’re curious if others have issues with the ethanol in pump fuel and what safeguards might make sense.

Eyes and Ears on ‘Em

Digital engine and fuel displays are good tools for keeping an eye on the health of the fuel delivery system as a whole. Their precise measuring capability with digital values also makes it easier to spot drops in fuel pressure and fluctuations in fuel flow. For external aux pumps, pay close attention during engine priming, noting if it takes longer than usual to generate fuel pressure. A failing pump might sound different, too, because faulty bearings might make a screeching sound when the pump is running. And as mentioned, check for leaks. This is obviously a no-go failure. If you smell fuel while priming the engine, investigate it before launching.

If you have to replace a pump, the choices are usually limited to the manufacturer of the one installed by the OEM, which was approved as original equipment. There might also be aftermarket replacements with PMA or STC to replace the original. Work closely with your shop for the right replacement, and as with many replacement parts, prices for fuel pumps are all over the board and also vary by condition. It’s worth comparing factory new versus overhauled pricing because there might be a narrow spread, with more warranty for a new one.

Aircraft Spruce is one of many sources for a good variety of exchange fuel pumps, offering Weldon, Dukes, Precision Airmotive, and Hartzell to name a few. It sells a PMA’d pump for the PA-28-161/181 series for $487 and with a one-year warranty. The engine-driven pump for Lycoming 360-series engines is around $950. McFarlane Aviation is another source, with an engine-driven pump for a Lycoming IO-540 priced around $2,500, plus a $700 core charge. At press time, many of these pumps had a two-month delivery time.

Your shop might save downtime and dollars by sending pumps to third-party overhaulers, and mechanics we talked with said using a high-quality overhaul facility usually means getting the pump back in a condition that’s essentially as good as new. One source that came up in our discussion with shops is North Carolina-based Consolidated Fuel Systems, specializing in the overhaul of Lear Romec fuel pumps on Lycoming engines (standard turnaround time is 14 days), plus fuel injection systems on Continental engines. The company has PMA approval for replacement components no longer available from OEMs. Hartzell Aviation is another, offering overhaul and new replacements.

Once the pump is overhauled, don’t underestimate installation effort because even though the pump is flow tested and set to meet the manufacturer’s flow specs during the overhaul process, there’s a good chance the fuel flow will have to be tweaked once it’s back on the plane.

As for preventive shotgunning or not, for some, there may not be much wrong with on-condition fuel pump replacement especially if you monitor its health, but sticking with the manufacturer’s replacement interval (and keeping the fuel filters clean) might boost your confidence in its reliability and if you’re lucky, avoid a failure at the worst possible time.