Fuel Pump Blues, take TWO.

[adjuster]

Okay, So since I bought my 2001 S8, the CEL would flash on WOT, but then go away, then it flashed at speeds over 120mph, and was fine at "normal" highway speeds.... (Around here, it's common to drive 82/83mph for hours and hours and hours.)

Well, I ran a few gallons of toulene in there to see if that would clean out any gunk, and it sure did. BUT it also took some life out of the pump too it appears, as now it's not happy if I try and go WOT or drive faster than 70mph...

So, I bought the wrong pump, then got the right pump, and when I went to remove the long bolt... POP, it's just turning the captured nut down on the venturi/siphon cup assy....

So, I have a car that runs great around town. And even at 55mph. But want to faster than 70? No dice. Want to acclerate at WOT for the onramp? No dice. (But it's plenty fast the rest of the time, and actually goes just fine, just flashes the CEL lamp.)

Here is my dillema.

The new housing is 800.00 or more.
The used ones are about 350.00 to 375.00.

I can get a in-line 255lph walbro pump for less than half that. (About a third actually.)

The pump in the tank/housing and siphon system all work just fine.

It's just not moving enough volume/pressure to feed the engine's needs at higher RPM, and under sustained load from what I can tell.

The in line Walbro would "suck" on the feed line to the injectors, I figure I'd mount it just after the stock Fuel Filter, in a section of "hose" there where it can be spliced in with minimal fuss.

Hook it up to power with a relay wired up to the stock system so it's only on when the stock pump is on, and it SHOULD be able to keep up with this engine's needs no problem, and I'd hope, the lack of "resistance" now on the old/stock pump in the tank would be able to allow it to feed the new in line Walbro just fine for many years to come.

Any ideas on this?

Has anyone done anything like this, or even considered it?

In my Supra days, we used to put twin in-tank Walbro's, and a few people did external fuel pumps with custom pick-ups etc. (All of them feeding 650rwhp engines needing far more fuel than this 360crank hp rated V8 will ever need.)

I know the in line Walbro's don't like to suck on the tank much. (IE: You want them close to the tank as possible, and have a easy source of fuel, but I've seen them draw through existing fuel pumps/systems with pretty good results, and where the stock pump on this A8/S8 is such a over-engineered mess, I'd rather just use it as the feeder system for a high quality external pump if I have to build my own, or spend 500.00 or more to try and get what's in this car to work correctly.

Thanks in advance for your advice guys.

[ainarssems]

Have you changed fuel filter? toluene is more lubricating then petrol so it should not have negative effect on pump. But it is possible that it lifted gunk from tank an blocked filter.

[adjuster]

Yep, sorry I left that part out.

I've changed the fuel filter out, and that had no effect, but there was some "jello" like crap in there, and it was very dark with crud. (I cut it open and inspected the paper media, and very little large sediment was in there, but the paper was dark with fine material that had been trapped. It's either the worn brush material, or metal from the communtator?)

I have no idea what the jello like crud was, it competely evaporated away when I dumped it out onto my concrete driveway.

So, I then pulled the fuel injectors, and had them cleaned and checked. They all passed 100%, no resistance problems, and only one picked up 1cc of flow improvement, so they were not dirty at all. (The shop owner told me there was none of the jello crud there at all, and no debris in the filters at the injectors, so the stock fuel filter had done it's job.)

That just leaves the pump starting to fail, or not producing enough volume to supply the engine under certain loads/RPM from what I can tell.

It does not run out of gas, even when it's down to nearly completely empty. When I tried to pull the pump, and the bolt just turns, I had it down to about 1 gallon. I put 21 gallons back into the tank when I filled up after realizing that this pump would not be coming out without surgery anytime soon.

I drive it nearly every day, around town it's fine, powerful, and runs perfect. But put it on the highway at speed, or race someone at the light, and it will flash the CEL light. (And on the highway, it drops out injectors, and makes the engine run rough until I shut it off, and start it again, then it's smooth as usual.)

[Conan_the_Librarian]

Just another thought; is the fuel pressure regulator lifting to early so not enough pressure is being delivered to the injector rail?

Adding a high pressure pump won't help if the regulator is not allowing pressure to build up in the rail.

[adjuster]

Good question? I don't have the fitting(s) needed to hook up into the fuel line, and check the pressure at the rail.

If the pressure regulator is not working, that would release too much pressure back to the fuel tank, and create a lean condition under load. (Good call to rule that out before I do anything else.)

Guess It's time I have the pressure checked, or buy the fittings/gauge, and check it myself.

Is it pretty common that the fuel pressure regulator fails on this vehicle? I've never seen one fail on any vehicle, they are pretty simple devices, just a diaphram and spring that regulates the pressure. (I've even seen ways to raise fuel pressure, by crushing the stock Toyota units, on turbo cars. **Using a vice, and socket, you crush the metal housing, compressing the spring more, and raising the base fuel pressure.**)

There are no leaks at the rail, or pressure regulator. And all the vac lines are hooked up at the regulator too, but I'll check the hoses again.

[ainarssems]

You can get new VDO pump same as original on aftermarket for around £120, no need to buy whole housing.