think I need a fuel pump

thunder669 · #1 10-27-2019, 10:01 AM

So I have had an intermittent issue that has raised the blood pressure. Twice I had the engine start sputtering in a climb at high power settings when i was at about a half tank in the left tank. I Immediately switch tanks and turn on electric pump and engine started running perfect again. natural assumption was that I had a fuel pickup problem. I eliminated this theory by disconnecting fuel line at carb and turning on electric pump. left tank pumped completely empty. so I next thought maybe a plugged vent line causing a bit of vapor lock and blew through the vent line to ensure it was clear. Then yesterday morning we flew to get breakfast and top the plane off at a nearby airport with cheaper fuel. shortly after takeoff a couple miles north of the field the engine started to sputter. but this time I had a full tank and was on the right tank. once again switching tanks and kicking on boost pump returned the engine to normal. After circling for a couple minutes I switched back to the right tank and plane continued to run normal. This was after I had leveled off and reduced power.

This leaves me thinking the mechanical pump is starting to fail since it has now happened on both tanks and kicking on the boost pump fixes the issue. the only other theory I have is I replaced the factory vents with the streamlined ones from JDair. Are these somehow not allowing enough air to flow when at max power in a climb attitude causing a type of vapor lock that the boost pump is able to overcome?

This is in my new to me RV4 with an O360. My wife loved flying in our Comanche and needless to say this has her a bit spooked about flying in the 4 so I need to make sure it is corrected and quick. Open to any other Ideas you guys might have

Mel · #2 10-27-2019, 10:19 AM

Typically when you have made a change followed shortly with a problem, the first thing to trouble shoot is to reverse the change and see if problem clears up.

Kyle Boatright · #3 10-27-2019, 10:31 AM

Do you have a fuel pressure gauge? If you're losing pressure, it'll tell you.

When my fuel pump went bad a few years ago, it was only obvious in climb, presumably because the airplane's attitude put the tanks lower relative to the rest of the fuel system and there was more head pressure to overcome.

thunder669 · #4 10-27-2019, 10:32 AM

I agree 100%. I had thought about just swapping the vents back and flying it, but being intermittent and having already flown it in a number of unusual attitudes with them is what makes me lean towards the pump. Hoping someone else has installed these and can chime in. also if it is the pump I'd like to get it on order as Im leaving town for a couple weeks and would like to have it here when i get back to minimize down time. This is what i hate about intermittent problems, how long before you can feel comfortable that it is fixed without actually finding the definite smoking gun???

thunder669 · #5 10-27-2019, 10:34 AM

it does not have a working fuel pressure gauge at the moment, a full engine monitor is on the short list of things to do over the winter as I want all the info I can get

Kyle Boatright · #6 10-27-2019, 11:47 AM

Quote:

Originally Posted by thunder669

I agree 100%. I had thought about just swapping the vents back and flying it, but being intermittent and having already flown it in a number of unusual attitudes with them is what makes me lean towards the pump. Hoping someone else has installed these and can chime in. also if it is the pump I'd like to get it on order as Im leaving town for a couple weeks and would like to have it here when i get back to minimize down time. This is what i hate about intermittent problems, how long before you can feel comfortable that it is fixed without actually finding the definite smoking gun???

I chased mine for a couple of weeks before I spent the money and time on a fuel pump. I pretty much ruled everything else out first, but only considered the pump to be the "likely" problem when I replaced it.

Sam Buchanan · #7 10-27-2019, 12:13 PM

Sounds like the same scenario I had when the mechanical pump started failing....a new Tempest pump made everything right.

Caveman · #8 10-27-2019, 12:14 PM

Quote:

Originally Posted by thunder669

Hoping someone else has installed these and can chime in. also if it is the pump I'd like to get it on order as Im leaving town for a couple weeks and would like to have it here when i get back to minimize down time. This is what i hate about intermittent problems, how long before you can feel comfortable that it is fixed without actually finding the definite smoking gun???

I've been flying for many years with the J.D. Air vents and had nary an issue, but this is on my RV7. Mel is giving good advice. It should be pretty simple to swap then back.
That said if the vents were installed properly, I'd wager it's a fuel pump issue. Is the motor driven fuel pump leaking out the tell tale drain hose?

jhk770 · #9 10-28-2019, 08:09 AM

I had this same issue with my IO-360 powered RV7A occasionally on climb out at full throttle. I replaced the pump, but problem still existed. While checking the fuel filters that I have for each wing, I discovered that the clamps that were used had crushed the lines just enough to restrict fuel flow at high settings. I suggest double checking your lines to make sure this is not the cause for your problem.

Jim

DanH · #10 10-28-2019, 08:40 AM

I'm with Mel; undo the recent change and see what happens.

That said, and given the RV-4 is new to you, why not check the engine logs to see when it last had a new pump installed? The rubber parts do not last forever. Merely suspecting the pump may be a good excuse to install a fresh one:

http://www.vansairforce.com/communit...16&postcount=5