Electric fuel pump questions

[arkvet]

I have a Saratoga with IO-540. A few weeks ago I started experiencing issues with idling. With the throttle all the way out the idle would fluctuate from 550-700ish. This fluctuation seemed greater than before but until I started having issues I have to admit I didn't watch it that closely. Sounded and ran fine, before.

The first indication of an issue was the plane dying on roll out. It was almost predictable. It would stay running until I turned onto taxi and the plane was nearing a stop. Then die. Ughh. If I kept just a little power in it would be fine. Throttle all the way out and it would die. It just simply wouldn't idle well. Anything above idle and everything ran perfectly. The JPI 830 showed no problems with any particular cylinders, etc.

I had my mechanic look at it and nothing could really be found. Of course when he did his expended runup is ran and idled fine.

Yesterday I went for a short flight and (in hindsight) I think the plane was talking to me before I even started up but I didn't know what it was saying. Generally when I turn on the fuel pump prior to start up (SOP for the IO 540) it kind of surges the first few seconds and then the pump slows just a tad. Yesterday it never slowed. It kept humming at that higher rpm. I do remember glancing down at the FF indicator and it did lift a bit. Not much, but it showed some flow. Plane started and gave me the same troubles. It would run great as long as I didn't take power completely out. Power to idle and it would eventually die.

I called my mechanic and he came by a while later. Electric fuel pump had gone inop. No click. Nothing.

Hmmm. So my theory is... The electric fuel pump had been failing over time and was either impeding just enough fuel flow or was allowing in some air that was effecting idle. The higher pump RPM I heard during preflight is because the diaphragm (or blades?) within the pump were not pushing enough fuel to create back pressure... and subsequently slowing the pump a little.

Sometime during that flight the electric fuel pump just decided to go entirely Tango Uniform.

I check voltage at the pump (between the capacitor and the pump) and it was 12.4 with the switch on and turned off the voltage slowly bled off.

Am I missing anything? My mechanic is fully involved with this issue btw. He's just backed up with a couple grounded planes and I'm trying to assist with some of the trouble shooting. He is thinking I'm on target with the symptoms I've seen and the fact that voltage is to the pump but it's not working.

Anything else I should check before ordering this $1,000 electric fuel pump? AND, would this failing pump potentially explain my issue with not idling well?

 

[Unit74]

Which pump is it? I recently did my Weldon 10080-B at The Aviation Group in Peachtree City who does a $650 overhaul with 8130, $850 OH exchange if they have one in stock. The work was solid and i've put about 100 hours since with not even a hiccup. Before you buy, give them a call. I shopped hard for a good shop at the best price. Quick turn around. It was a couple days plus the shipping time.

 

[arkvet]

It's an Airborne 1B5-6. I looked at all the usual places and have one on order from Quality Aircraft Accessories out of Tulsa. Not too far from home. Everyone seemed to want right at $1,000 for them. Merry Christmas to me.

I'm anxious to see if replacing the pump eliminates the issue with the idling / dying. The idea has been bounced around a few mechanics and none of them are certain they've seen this before. The current theory is that the dying pump was letting a little air into the system and it was only noticeable at very low fuel flow setting (idle)

 

[Clip4]

How can air get in and fuel not leak out?
I believe you may have two issues that coincidentally occured about at same time.

 

[flyingron]

Air very much can get into the fuel system without fuel leaking out.

 

[arkvet]

How can air get in and fuel not leak out?
I believe you may have two issues that coincidentally occured about at same time.

Easy, a working check valve. Or simply that the leak requires enough pressure to occur and static tank pressure isn't enough for a fuel leak (with or without check valve). Start the engine and negative pressure occurs when the engine driven fuel pump is sucking fuel UP from the low wing tanks.

Air very much can get into the fuel system without fuel leaking out.

 

[Unit74]

It's an Airborne 1B5-6. I looked at all the usual places and have one on order from Quality Aircraft Accessories out of Tulsa. Not too far from home. Everyone seemed to want right at $1,000 for them. Merry Christmas to me.

I'm anxious to see if replacing the pump eliminates the issue with the idling / dying. The idea has been bounced around a few mechanics and none of them are certain they've seen this before. The current theory is that the dying pump was letting a little air into the system and it was only noticeable at very low fuel flow setting (idle)

Really consider an OH of your own. QAA is selling you a OH at premium cost.

 

[Checkout_my_Six]

Fuel pressure is measured at the divider. What’s the pressure doing?

If you’re not seeing any fuel pressure fluctuations... my next inspection is the divider. It will cut out flow at low pressure....if the spring is failed or worn.

 

[arkvet]

Really consider an OH of your own. QAA is selling you a OH at premium cost.

Yeah I know that was an option but honestly didn't expect it to save me just a ton of money and it would add to my down time. I've got some loosely scheduled flying coming up. I checked lots of places and the cost for a rebuilt one was so dang consistent (all requiring a core) it leads me to believe OH my own wouldn't have saved a ton.

Fuel pressure is measured at the divider. What’s the pressure doing?

If you’re not seeing any fuel pressure fluctuations... my next inspection is the divider. It will cut out flow at low pressure....if the spring is failed or worn.

Gotta admit I have no clue what or where the divider is. These will be great questions to answer if the new pump doesn't resolve the issues. I'm having a hard time believing that this electric pump has decided to fail at coincidentally the same time as another probable fuel flow issue has developed. Anything is possible though I suppose.

I haven't noted an issue with fuel pressure, but I admit with a JPI 830 I'm looking at FF quite often. The old needle could have been twitching and I may not have noticed.

 

[Clip4]

Easy, a working check valve. Or simply that the leak requires enough pressure to occur and static tank pressure isn't enough for a fuel leak (with or without check valve). Start the engine and negative pressure occurs when the engine driven fuel pump is sucking fuel UP from the low wing tanks.

So you believe an electric fuel pump failed in such as way that air is drawn from outside the case into the fuel line at idle, but fuel that has been warmed under a warm cowling when the engine is off is not expanding back out of the pump case.

How about crud from a failed fuel pump affecting the fuel control unit?

 

[Checkout_my_Six]

The divider is on top of the engine...octopus looking thingy. All fuel flows thru it to each injector. The fuel pressure is also measured at this point. If your fuel pressure was not fluctuating I doubt you have pump issues.

 

[arkvet]

The divider is on top of the engine...octopus looking thingy. All fuel flows thru it to each injector. The fuel pressure is also measured at this point. If your fuel pressure was not fluctuating I doubt you have pump issues.

Gotcha. Yeah I looked up divider after my post and realized what it was. I just didn’t know what it was called.

I can assure you I have fuel pump issues. It was alive and is now dead.

How about crud from a failed fuel pump affecting the fuel control unit?

To be honest this was my first thought. My mechanic is the one that suggested the air theory.

Once the new pump is installed we’ll see if any issue remains. If it does then we’ll have to start looking for debris / obstruction. My mechanic said from the beginning he felt it was a fuel flow issue but couldn’t pinpoint the origin until the electric fuel pump decided to die.

 

[Unit74]

Call Peachtree tomorrow and see what they say.

 

[Raymo]

Pressurize the intake with a shop vac and look/feel for induction leaks, which only affect low RPM ops. I agree, sounds like more than one problem going on.

 

[arkvet]

Pressurize the intake with a shop vac and look/feel for induction leaks, which only affect low RPM ops. I agree, sounds like more than one problem going on.

Would you care to elaborate just a little on this procedure?

 

[Raymo]

Would you care to elaborate just a little on this procedure?

Tape/plug the exhaust, put the shop vac in pressure/blowing mode and have it push air into the intake. You may need to make an adapter of some sort to allow some amount of pressurization. Then a spray bottle with soapy water can be used to search for leaks. Induction tubes are the most common area, of course.

 

[arkvet]

Got the OH'd boost pump installed and the initial runup testing demonstrates that all issues have resolved. The idle is (in my ears) smoother than it's been in a long long time.

I will also note that during the prestart prime the new boost pump spiked the fuel flow needle on the MP gauge within a few seconds of turning it on. Idk if that is normal as the previous pump had never spiked the needle in the 3 years I've owned the plane. I've simply noted that the previous pump would barely lift the needle (2-3gph?) during prime

I'll update the thread again if any of the symptoms return.

My mechanic and I agree that air being sucked into the system through the faulty pump is the likely culprit. The reasoning for this is that if it were a fuel flow restriction (at that pump) it should have been notable as well at higher fuel flow / power settings. Also, the poor idle existed with the pump turned on or off, didn't matter.

Thanks for the all the advice!

FWIW I paid for the SAAVY analysis service too. I had been a free member for a while but thought it might be a good idea to do some diagnostic flights and get the overall engine performance evaluated. Pretty cheap considering what they're able to tell.