Something I've noticed...

Before each flight I run the engine on both pumps to make sure they both work. I haven't yet switched over to the back-up pump in flight, but after landing on the taxi in, if I switch to the backup pump, the engine quits. 

The pump works, but there must be air in the line I'm guessing. It's not there before flight, but after something must be holding up the fuel.

When I restart the engine, I can switch between pump 1 and 2 all day long with no issue. It's just that initial switch after landing.

Any ideas?

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Mark,

Are both of your pumps manually switched, or is one controlled by the ECU?

Did you perform SB 2019-02?

Any update on this?

Jimmy, SB 2019-02 was not done on this engine so I'm holding off on flying until I order the parts and complete it. But, I don't think this SB will fix the issue I'm having. But I'll complete it and test it. If I'm still having the same issue then I'll contact the good folks at UL Power and ask for their analysis. I'll post the results once I test it. 

Mark, that sounds kinda interesting...curious as to what you find.

Almost sounds like the standby pump is having air drawn into it over the flight duration, then vapour locks when selected on. This sometimes happened with standby pumps in the industry I worked in.

Interested in what UL says.

Hey Mark, while I was doing some flight testing the other day, I did multiple switching of the pumps; preflight runup, inflight and postflight during taxi.  No apparent interruption of fuel to the engine - kept on running smooth without a stumble of an sort. I do have the SB 2019-02 install on the engine (350iS).  Just another data point for you....

Ive had the parts on order from Wicks for a couple of weeks to complete the 2019-02 SB, but they were on back order. I just received an e-mail yesterday that the parts were shipped out so I should have them in a day or so. So once I complete the install, I'll hope that it solves the problem.

Mark,

Noticed a similar issue with my engine. I switched in cross country flight today and had a brief, very brief, moment of silence before switching back to pump 1. Tested again while circling over a local dirt strip, again silence. Switched while slowing down on runway, silence. Parked in front of the hanger, switches fine. I am going to swap filters, test, and then go to next idea. Maybe next time in flight if it fails to switch I will be able to wait and listen for pump noise before restarting engine. Maybe.

Ralph

N750RP

All,

While testing for leaks after replacing the filters I noticed that the two pumps came up to pressure in about the same amount of time, however they sound different from each other while operating. Do the pumps sound the same on yours? When and if the winds here drop down I will flight test the filter change, not holding out much hope that is was the filters causing the problem.Thinking about ordering a new pump come Monday.

Ralph

All,

Good news! Went up for a test flight tonight and switched fuel pumps. At first there was silence, but then if I waited long enough...the second pump would come up to pressure and the engine would restart. The wait was 5-15 seconds? Seemed longer. When switching while taxiing the lag was long enough that the engine would die and require use of the ignition starter to fire up. 

The winds aloft were 30-40 mph tonight but smooth. Good flying weather, flying around a point would have been tough.

Ralph

Hey guys. I’m watching this discussion with interest as I have the same engine/pumps as you two. Sounds like you both have a one or the other pump circuit. Wondering if installing a separate switch for each pump, allowing the standby pump to be selected on before shutting down the running pump, would fix the problem? Wouldn’t help in a real time running pump failure but at least be able to have a smoother transition for the planned or partial failure scenarios. I have installed 2 switches but am not quite at the engine test run point yet.

John

John,

The question is, is there a problem? Dual fuel pumps are there in the hopefully rare case where one fails. How often does that happen? If the pumps have a known life scheduled replacement might be an excellent solution to the weight penalty of a second pump. Next, rather than a complicated switch system, adding switching and testing pumps as part of preflight would appear to reduce some concerns of a lag on switching over during climb out. The other common way of addressing the issue is to run both pumps during takeoff or landing. I lost a fuel pump in a 172xp during climb out and having a second pump to switch to did not save me from a forced landing. When flying really low and the engine quits you do not have time to trouble shoot, you are to busy  flying the plane. The conclusion is that there may not be a clean simple solution of this possible issue.

Ralph

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