Mechanical Fuel Pump Recommendations

Hello All -

On my -10, running full rich during climb, I sometimes get the infamous low fuel alarm that so many others get. So I flip on the aux....no big deal.

If I run a bit lean in climb, then the mechanical pump keeps up with the flow rate. But I really prefer to run rich in climb (cooling, etc).

So, my question:

I have checked out the fuel system for leaks, etc....I did find one and fixed it (in the channel, downstream of the aux pump). The channel is insulated and cool to the touch. Basically, I don't think I have a heat issue or any leaks. I think the mechanical just cant keep up.

So, is there a more capable mechanical pump that I can install ?

Thanks,

Scott

I am not familiar with the infamous alarm you are referring to.

In order to answer your question, we need more information.

Particularly I am wondering if you are truly having a low fuel pressure issue. Are you injected or carb'ed and what are seeing for pressures on the engine driven pump?

This would be a good starting point.

CJ

Injuected.

A lot of -10 guys report issues with low pressure alarms during climb out, esp on hot days. I have learned to be ready for it, or run a bit lean in climb.

During cruise I run 12-13 GPH and 25-ish PSI with the mechanical. It works fine and does the job.

Only during the 25-26 GPH climb out do I occasionally get the alarm.

Could be vaporization at the inlet or it could be that the pump is just not able to keep up.

I'm not concerned about it. I am fine with running the aux in climb.

Its just a tweak that I am looking into.

If you consider that the same engine with the same mechanical fuel pump seems to do ok in other applications at the same fuel flows, then you need to look at what's different in your application. The most obvious possible cause (re-enforced by the fact that boost pump use cures it) is that the mechanical pump is being starved for fuel (trying to pump vapor).

Assuming that's correct, the next goal is to find out why. (Long runs; too-small lines; sharp bends; obstructions; air leaks; etc)

Not saying it's *your* problem, but it's worth noting that you can have air leaks in a fuel system that never leak fuel. One of my neighbors fought a randomly rough running injected engine for years before finally replacing his flexible fuel lines. Cured the rough running. IIRC, he found that if he did a 'soapy water' test (like we test our tanks) on the pressurized lines, he'd get bubbles on the outside. Never had a fuel leak.

FWIW...

edit: Forgot the obvious. What does Lyc say is minimum safe pressure? And. What pressure do you have your alarm set at? (Reminder: Low fuel is not the same thing as low fuel pressure. )

Hi Scott. I think you can afford to lean a little bit in climb. You didn't state at what altitude you were getting 24-26 gph ff, but my TCM IO550 300hp is about that ff at takeoff at 2000' msl. Just watch EGT (keep them about the same as TO) and CHTs.

I have not looked at the filter. It could need changing or cleaning.

I also have 9.5:1 compression, so, my fuel is higher than most (if only by a little).

The plumbing in the channel is completely standard and per plans (I have looked at it extensively). The fuel line runs are normal and fuel system overall is completely per plans. The aircraft was built by a man (Steve Raddatz) who had built over 20 RVs. This was his fourth -10. Very reputable and well-regarded.

My alarm is set at 11 PSI (if I remember correctly).

Yes, I agree. I am probably pumping vapor...But the channel is cool. And forward of the firewall, the fuel lines are insulated. The mechanical pump has a shroud and a scat tube for cooling. All of this looks pre-finish, not post...

The engine has never stumbled and the aux works great.

Its just a mystery I would like to solve.

istrumit said:

Injuected.

(Snip)

25-ish PSI with the mechanical.

Click to expand...

If the fuel controller on your plane has the same specs as mine, the nominal pressure is 20 psi.

At 25 psi, you are fine.

What are your alerts set at?

I see in a later post that you mention 11 psi or something? Is that your lowest indicated pressure? If not, what is it?

CJ

I have never noticed what the lowest pressure range on the panel is. It's less than 11 PSI. 11 is where the yellow arc starts.

Thinking back, it typically reads 21-23 PSI in cruise (w/o the aux), not 25.

I have been leaning a bit in climb...but, I find that I can keep the CHT below the yellow line and max climb at gross weight only if I stay rich.

And yes, the max flow rate does taper off with altitude. Typically, if I am going get a low pressure alert, its when/if I turn off the aux at around 3000 AGL during climb.

Overall - like I mentioned, this is a very minor thing, but, sometime soon I am going to have a few things done (move the OAT probe, change the static ports...etc) and I thought I might change or replace the fuel pump at that time if it was warranted.

Hard to tell...

I always use the boost pump for take off and climb. It's also on when I switch tanks or do my pre-landing check list. I don't usually turn it off until I reach altitude and trim for cruise.

~Marc

I always leave the electric fuel pump on until top of climb. Otherwise you ar asking the mechanical pump to suck the fuel uphill. A climb has the highest temps underneath the cowling with the lowest airflow. Try leaving the pump on and you may not have to solve anything.

That being said, I noticed that my stock fuel pump on my IO-540 was running the pressure pretty consistently around 22 psi, which is actually ok. However, I did change out the pump to a tempest fuel pump and the pressures ran consistently around 27-28 without changing anything else. My new Thunderbolt engine also runs 27-28, so it I should possible the diaphragm in the pump doesn't always put out the same pressure over the life of the pump.

Vic

vic syracuse said:

so it I should possible the diaphragm in the pump doesn't always put out the same pressure over the life of the pump.

Vic

Click to expand...

I have seen evidence of the pressure degrading on the high pressure pumps as they age.
I agree with Vic that in hotter temps it is best to leave the electric pump on until level off.

Vic - can you tell me the model of Tempest that you used, assuming it would be the same for me?

Mine is a Penn Yan Aero io-540 with 9.5:1 compression and roller cams, otherwise its stock.

Scott

I have a Tempest pump on my 4 banger it consistently holds 27-28 PSI. When new, it was often higher, even at idle.