• olaaf
  • Ripened Lemon
  • Offline
  • From: New York, NY
  • Registered: 2010-11-05
  • Posts: 368

Topic: walbro fuel pump failure mode

So,

We had problems at MMC and we *think* our fuel pump is failing. The pump was a used Walbro 255l external purchased from a friend.

The symptoms were that after 30 minutes of good performance on Saturday morning, and then the engine would lean out under moderate load ( 40kpa, not even boosting). We tore apart our ignition system (hastily replaced Friday night after learning that COP’s can’t run in waste spark for more than 5 minutes on the same ignitors) over and over again, and then looked at the fuel system 6 hours later. Filling the cell with fuel (had 6 gallons left in the tank) seemed to work fine late in the afternoon for the last hour. We kicked ourselves and thought we were simply fuel starving, despite the other evidence.

On Sunday, the car seemed fine for 2.5 hours and then when I took my stint, it would lean out again under heavy load (greater than 100kpa- boosting). After checking the filter, fuel cell (ATL 22 gallon with the surge tank), nothing seemed amiss. Fuel pressure while idling was always 40psi, though we were using a tire pressure gauge on the schrader valve on the rails that would hold peak pressure. Instrumentation was definitely lacking.

We tried one more time late on Sunday, and now the car could barely move itself (and didn’t have enough power to enter the track, and I was able to get it turned around before needing a tow). Fuel pressure when running is still 40spi, but when we shut it down it fell to 25 psi. 10 seconds later it’s 10 psi, and then 10 seconds later it’s 0 PSI in the rails. No fuel leaks anywhere (All AN fittings in braided hose).

It MUST be the fuel pump (no stuck injectors), right?

I understand the Walbro to be a rotary cell type pump, with an integral check-valve to keep pressure in the rails. It seems the check valve has failed? In researching, It seems that these pumps are often sold with cushion sleeves (which of course, I don’t have- I’m hard mounted to the fuel cell cage with U-bolts). Are the cushions for passenger comfort, or fuel pump longevity?

What are the common failure modes of these sorts of pumps?

I’m interested in replacing the pump with something that is redundant. Are 2x or 3x Mercedes 190 pumps good enough to keep a 350+hp engine going?

And yes, we are adding a real time fuel pressure sensor to the digital dashboard.

Thanks
olaaf

Flying Rat Motorsports- Turbo Taxi, RIP
  • From: CT
  • Registered: 2010-09-20
  • Posts: 258

Re: walbro fuel pump failure mode

How many races have you run on the Walbro? If you've run a few with no problems than yea the pump is probably just dying.

How do you have the lines run? Feed/return or dead headed pump? What size lines feeding the pump? How do you have the pickup setup in the cell? Have you been sucking any air through the pump?

We had a very similar issue in Jersey last year and it was our first and last time running a 255 Walbro external pump.

We've got a 22gallon cell and anywhere below 3/4 full the pump would whine and act like it was starving for fuel. Ended up being that our pickups were too small and we probably didn't have the pump mounted low enough relative to the tank itself. The pump was making all sorts of terrible noises so we replaced it with an internal setup. Turns out the pump was actually fine and we've got it mounted on our dyno stand.

I think those cushions with the standard kit are just there to dampen some noise although I'm sure they also dampen some vibration which could help prolong the pump's life.

If you've run a few races on the Walbro than I'd suggest just buying a new one. If it worked before, it'll work again. Why bring on the pain and new set of problems with another pump setup which may or may not work on your setup?

Maximum Efforts Motorsports
Mid-Engine Chevette
S-10 incoming...
  • olaaf
  • Ripened Lemon
  • Offline
  • From: New York, NY
  • Registered: 2010-11-05
  • Posts: 368

Re: walbro fuel pump failure mode

We have run 2 races with this pump without issues. It’s a return style system, 6an lines throughout. We are using an ATL 3 door surge tank, with its integral pickup. We never really went low enough on fuel to suck air. Our pump is mounted low- on the same plane as the bottom of the cell.

The reason I’m inclined to switch pumps is ease of accessibility: Just like our ignition problem on Friday night- option 1 was to source 4 new Bosch BIP373 ignition transistors (impossible) or to get old style ford EDIS coil packs (Rob had some spares for his team car). Racy Walbro pump with AN fittings vs Junkyard/Parts store pumps..

Flying Rat Motorsports- Turbo Taxi, RIP
  • Baron
  • Baron
  • Lemons Staff Stalker
  • Offline
  • From: DFW
  • Registered: 2009-05-01
  • Posts: 2,408

Re: walbro fuel pump failure mode

Ill put this out there: it doeesnt matter what pump you are runnnig, if the car is sitting for months at a time (like ours does between events) it will die a premature death. The e10 fuel is not agreeing with a lot of things, and the fuel pumps are one of them. I sell wholesale recycled parts for a living, and we now sell fuel pumps frequently, 8 years ago we couldnt give them away.

Grab a couple of new walbro 255's and throw one in the box as a spare. Ive also heard that they like to be as close to the pickup as possible, as they dont like to suck fuel very much. Maybe moving to the top of the cell right off the pickup fitting would be better?

Team Lost in the Dark
Winner " I got screwed" and "Jay's dream car"
2012 Gulf region champs

5 Reply by RThodal (edited by RThodal 2013-04-10 11:02 AM)

  • Registered: 2010-02-08
  • Posts: 85

Re: walbro fuel pump failure mode

I know you said you checked out your fuel filter but you may want to take a look at my thread regarding fuel from the Mobil at MMC

Team Rust in The Wind #301
1987 Nissan 300zx 2.3L Saab Turbo
https://www.facebook.com/RustinTheWind24HOL
  • olaaf
  • Ripened Lemon
  • Offline
  • From: New York, NY
  • Registered: 2010-11-05
  • Posts: 368

Re: walbro fuel pump failure mode

RThodal wrote:

I know you said you checked out your fuel filter but you may want to take a look at my thread regarding fuel from the Mobil at MMC

we will pull the sock filter on the pickup hose in the cell- we only checked the aftermarket inline filter...

Flying Rat Motorsports- Turbo Taxi, RIP
  • Registered: 2009-05-27
  • Posts: 361

Re: walbro fuel pump failure mode

An In-tank pump is usually the better bet..... Electric pumps like to "push" rather than "pull" fuel.... The In tank fuel cools the pump as an added benefit.... Food for thought.... How many OEM pumps are External to the fuel tank? None that I can recall in the last 20 years....Might just be your fix.

8 Reply by hkerekes (edited by hkerekes 2022-01-15 09:08 PM)

  • Registered: 2020-10-11
  • Posts: 89

Re: walbro fuel pump failure mode

wrong post