[MacCool]

Lycoming IO-320 D1A on my RV-9A. I've been getting mild fuel pressure fluctuations, primarily on the ground when the engine is hot. Only shows on the gauge, no engine stumbles or other symptoms, but occasional dips into the red on the EFIS fuel pressure gauge. New kavlico pressure sensor recently replaced. My A&P checked with a mechanical gauge and confirmed that there is some pressure fluctuation when hot. This will be the third fuel pump in this airplane in less than 500 tach hours. Previous two pumps have been Tempest pumps AF15473. Our concern is pump cooling. Apparently the cooling shroud most commonly available requires a fair bit of grinding to fit a Tempest fuel pump.

Thoughts on cooling shroud vs a directed scat tube?

 

[KiloFoxtrot]

Hope this helps or gives you ideas to cool without using a shroud. I included a very rough drawing of what I did for the cooling the Pmag and the mechanical fuel pump.

 

[hgerhardt]

Question to all of you who've added a shroud after flying for a while without one to correct what the OP is complaining about: did adding the shroud actually help?

My IO-360 does that too when hot on the ground, and turning on the boost pump fixes that annoyance.

It seems logical that much more heat is conducted into the aluminum pump housing by being bolted to a hot crankcase, than you could get rid of through a bit of cool air surrounding the pump, but I'd love to be proven wrong on that assumption.

 

[Roadjunkie1]

Lycoming IO-320 D1A on my RV-9A. I've been getting mild fuel pressure fluctuations, primarily on the ground when the engine is hot. Only shows on the gauge, no engine stumbles or other symptoms, but occasional dips into the red on the EFIS fuel pressure gauge.

Red low or Red high readings?

New kavlico pressure sensor recently replaced. My A&P checked with a mechanical gauge and confirmed that there is some pressure fluctuation when hot. This will be the third fuel pump in this airplane in less than 500 tach hours. Previous two pumps have been Tempest pumps AF15473. Our concern is pump cooling. Apparently the cooling shroud most commonly available requires a fair bit of grinding to fit a Tempest fuel pump.

Thoughts on cooling shroud vs a directed scat tube?

O-320 D1A, RV-4. I have a simple scat tube directed at the top, port (fuel outlet) side of the (standard Lycoming) mechanical pump and, after 1200 hours, have had no issues. RV-4s are notorious at being better at cooling things than other types, the -3 maybe being the exception. Do you have a cooling tube in place now? If not, I would start with that. WAY easier than trying to mangle a shroud into place back there..... PITA to be replacing fuel pumps........

 

[MacCool]

My current concern about cooling isn't about pump performance/pressure fluctuation, it's about the hot environment leading to premature engine driven pump failure. The pump I have coming from Spruce will be the fourth engine-driven fuel pump for this airplane in 443 tach hours since the engine was new. Seems excessive. I've already assumed this pump is in pre-failure mode. So, leaping to the conclusion that my excessive (IMHO) fuel pump failure rate is heat-related, I'm looking for the best way to cool the engine driven pump. It appears that installing a cooling shroud on a Tempest pump would be a more complicated endeavor for an already PITA task, but I'm willing to have my A&P do it if there's a clear benefit over a simple scat tube. Hence...my question.

 

[MacCool]

Red low or Red high readings?

Red low.

 

[Roadjunkie1]

My current concern about cooling isn't about pump performance/pressure fluctuation, it's about the hot environment leading to premature engine driven pump failure.

Has anyone taken one of the failed pumps apart to see what fails? I would think, hot environment or not, a pump that last 100 hours might be something wrong with what is driving the pump inside the engine. Yes: that is excessive!! Not to mention $500 a whack to replace it!! Is the pump arm being moved so far that it is rupturing the diaphragm? Anyone else with a -9A (or any model) experiencing similar failure rates?? What does your A&P say? Has he seen this type of failure in other (RV or non-RV) aircraft before? Mooneys? They are pretty tight back there. I've not heard of that. Did you chat with Lycoming? Curious minds want to know.....

The pump I have coming from Spruce will be the fourth engine-driven fuel pump for this airplane in 443 tach hours since the engine was new. Seems excessive. I've already assumed this pump is in pre-failure mode. So, leaping to the conclusion that my excessive (IMHO) fuel pump failure rate is heat-related, I'm looking for the best way to cool the engine driven pump. It appears that installing a cooling shroud on a Tempest pump would be a more complicated endeavor for an already PITA task, but I'm willing to have my A&P do it if there's a clear benefit over a simple scat tube. Hence...my question.

Try the scat tube first. Getting any cooling air back there would be helpful.........IMHO......

 

[MacCool]

Has anyone taken one of the failed pumps apart to see what fails? I would think, hot environment or not, a pump that last 100 hours might be something wrong with what is driving the pump inside the engine. Yes: that is excessive!! Not to mention $500 a whack to replace it!! Is the pump arm being moved so far that it is rupturing the diaphragm? Anyone else with a -9A (or any model) experiencing similar failure rates?? What does your A&P say? Has he seen this type of failure in other (RV or non-RV) aircraft before? Mooneys? They are pretty tight back there. I've not heard of that. Did you chat with Lycoming? Curious minds want to know.....

Try the scat tube first. Getting any cooling air back there would be helpful.........IMHO......

Yeah, my inclination thus far is just the directed scat tube and my A&P doesn't disagree. He has experience with that in some of the bigger Lycomings. My prop governor is right there. The less work done back there the happier he will be. The shroud idea is rather unappealing.

My first pump failure occurred on the flight back when I bought the airplane. Engine wouldn't run after refueling at Mason City. It was Sunday afternoon and the nearest A&P was in in Forest City...we made the 20 mile flight on just the boost pump (route took us exacty over the crash site where the music died). He was a really nice guy, replaced the pump. Forensic evaluation indicated a pinhole with tear, I'm told (we had left by that time). Certainly, the current one will be dissected after the swap.

My transition CFI supervising....

 

[DanH]

Red low.

Red low says the fuel is flashing to vapor when the pump lowers pressure in the hose leading to the pump. Can't generate pressure when trying to pump vapor.

Put another way, the fuel is already hot before it gets to the pump.

 

[MacCool]

Red low says the fuel is flashing to vapor when the pump lowers pressure in the hose leading to the pump. Can't generate pressure when trying to pump vapor.

Put another way, the fuel is already hot before it gets to the pump.

Understood, and thank you. That was what I was forlornly pinning my hopes on, but it's a new event. For a hundred hours after I replaced the failed pump, there was no such issue and nothing else has changed. This is new.

My A&P isn't sure. Could be vapor-related, could be a failing engine-driven pump. I've already addressed wrapping the fuel lines and exhaust shielding. Engine-out problems in-flight tend to be inconvenient and I have a Young Eagles coming up on June 1 with 5 pilots scheduled to fly 87 kids....so...additional data for the matrix. I'm replacing the pump...at this point mostly concerned with preventing another fuel pump failure within the next 150 hours.

 

[DanH]

Understood, and thank you. That was what I was forlornly pinning my hopes on, but it's a new event. For a hundred hours after I replaced the failed pump, there was no such issue and nothing else has changed. This is new.

My A&P isn't sure. Could be vapor-related, could be a failing engine-driven pump. I've already addressed wrapping the fuel lines and exhaust shielding. Engine-out problems in-flight tend to be inconvenient and I have a Young Eagles coming up on June 1 with 5 pilots scheduled to fly 87 kids....so...additional data for the matrix. I'm replacing the pump...at this point mostly concerned with preventing another fuel pump failure within the next 150 hours.

Hey, could be a pump. For example, a pinhole in the fuel diaphragm can allow air into the pump chamber via the tell-tale fitting.

Back to heat. Don't guess, measure. An ordinary LM34 on the end of a three wire cable can be fastened to the pump body, or a hose, or just measure air temperature. All you need for a meter is your digital voltmeter. If it says (for example) 1.45V, just move the decimal point two places...145F.

https://www.ti.com/lit/ds/symlink/lm34.pdf

 

[MacCool]

Hey, could be a pump. For example, a pinhole in the fuel diaphragm can allow air into the pump chamber via the tell-tale fitting.

Back to heat. Don't guess, measure. An ordinary LM34 on the end of a three wire cable can be fastened to the pump body, or a hose, or just measure air temperature. All you need for a meter is your digital voltmeter. If it says (for example) 1.45V, just move the decimal point two places...145F.

https://www.ti.com/lit/ds/symlink/lm34.pdf

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[IMAGE]

Yeah, I'm curious about it so I did order some LM34's from Amazon (a 10-pack is $7) and I'll look at the under-cowl temps in a variety of flight phases.

Looking ahead though, I'm curious...if I conclude that those engine room temps are too high while taxiing and in the pattern, and affecting fuel flow and/or under-cowl component reliability (three fuel pumps and two Red Cubes), would Alan's EX Cool Cowl Flaps be a reasonable addition? As a data point, I'd mention that neither CHT's on climb nor oil temps are of any concern....all normal.

 

[DanH]

Air temperature is of interest, but what you really want to know is fuel temperature at the pump inlet and outlet.

 

[MacCool]

Air temperature is of interest, but what you really want to know is fuel temperature at the pump inlet and outlet.

Yeh, why not? I have 10 sensors.

 

[petehowell]

You could cool the pump with bypass fuel flow, too - see my recent post on a vapor return line. Also, those LM34's on Amazon might be counterfeit - if not the price is really good. I am building a multichannel data acquisition gizmo to display and record temps, once I get the parts delivered. If it works, you can borrow it.

Let's talk at the RV picnic here in a few weeks.

 

[MacCool]

You could cool the pump with bypass fuel flow, too - see my recent post on a vapor return line. Also, those LM34's on Amazon might be counterfeit - if not the price is really good. I am building a multichannel data acquisition gizmo to display and record temps, once I get the parts delivered. If it works, you can borrow it.

Let's talk at the RV picnic here in a few weeks.

That would be great...I'll look for you.

 

[MacCool]

Brief update...my A&P replaced the Tempest 15473 high pressure fuel pump yesterday. We did that kind of empirically...I was inclined to think that the pressure fluctuations were heat-and-vapor-related rather than pump failure...didn't affect engine performance and didn't occur in the air. I have a bunch of temp sensors for the fuel lines but haven't had a chance to build them yet, and we have a big Young Eagles event tomorrow. I did have the pump, and he was doing the annual CI anyway, so...

I flew the plane for an hour or so today (75°F), oil temps 170°F. I immediately noticed that it idled smoother when it got up to temp. Long taxi and long slow approach and I noted that there was zero fuel pressure fluctuation. Where before under the same circumstances I'd see the pressures occasionally drop to as low as 11 PSI, I'm now seeing them consistently run 23-24 PSI, steady as a rock, at all times.

So I'll still check the undercowl temps, but now doing that because I'm wondering if excess heat is the reason that this is the 4th engine-driven fuel pump in 444 tach hours. Thinking about a scat tube, but my A&P kind of likes the idea of the Antisplat Cowl flap. All this, if for no other reason, because I'm also on my second Weldon boost pump and second red cube (both on the firewall).

Going to do an autopsy on the bad fuel pump when I get a chance.

 

[RV7ator]

For those of you still thinking of a pump shroud...don't do it. They make installation, hose attachment, and tool access for nut tightening next to impossible, and take up that much more volume in a crowded area. I tried to use the one delivered with my engine because it was there. Bad idea. I cut it off with a dremel tool and ripped the tabs from beneath the mounting screws it was so in the way.

John Siebold

 

[MacCool]

For those of you still thinking of a pump shroud...don't do it. They make installation, hose attachment, and tool access for nut tightening next to impossible, and take up that much more volume in a crowded area. I tried to use the one delivered with my engine because it was there. Bad idea. I cut it off with a dremel tool and ripped the tabs from beneath the mounting screws it was so in the way.

John Siebold

That's completely consistent with what I read about experiences with that cooling shroud online, especially for the Tempest pump. The idea is interesting but I doubt that in the end it would be superior to a blast tube. I'm still wondering about the value of anti-splat cowl flap.

 

[Kyle Boatright]

That's completely consistent with what I read about experiences with that cooling shroud online, especially for the Tempest pump. The idea is interesting but I doubt that in the end it would be superior to a blast tube. I'm still wondering about the value of anti-splat cowl flap.

I suspect the pump will get heat soaked after shutdown. Not sure a cooling shroud, blast tube, or cowl flap will result in much improvement in that situation.

 

[vic syracuse]

I would check all of you lines aft of the pump all the way to the tanks, including the selector valve, especially if it is the standard Van’s selector valve. It has an o-ring in it that can leak and suck air, which will also show up as low pressure.
vic

 

[MacCool]

I would check all of you lines aft of the pump all the way to the tanks, including the selector valve, especially if it is the standard Van’s selector valve. It has an o-ring in it that can leak and suck air, which will also show up as low pressure.
vic

Excellent tip, Vic. I don't think that's what's going on here since replacing the fuel pump got rid of all of the furl pressure fluctuation. However, to my knowledge, that fuel selector valve has never been disassembled and no doubt is something that should be looked at. Thanks