Walbro woes

[AlunJ]

Ok folks, here's an interesting find that I could really do with some advice on.

I've spent a chunk of today tracking down the on-load det issue on the black MR2 (this is the same det issue that stopped us mapping the 2.2 block any higher than 1.1 bar). Having eliminated most of the other possible causes of detonation I turned my head to the fuel system and thought "hey, lets do some flow testing of the pump to see what it's actually doing". What I found was horrifying. So this post is partly a "this is what I found, be aware of" and partly a "what can I use to replace this pump". Note that this is a Walbro 255 high-pressure pump that should be good for in the region of 500 horsepower.

• Base flow (at fuel filter exit) - 224 Liters per hour. Not quite the expected 255 but not too far off.
• Flow at fuel return (fuel pressure regulator at atmospheric pressure) - 153 liters per hour. 40% flow reduction.
• Flow at fuel return (1 bar supplied to FPR pressure reference) - 115 liters per hour. 55% flow reduction.
• Flow at fuel return (1.7 bar supplied to FPR pressure reference - this being the peak boost it's to be mapped to) - 76 liters per hour. 71% flow reduction... :omg: errrrr... yeah...

At this point I'm not really happy using the Walbro. Maybe as a lift pump but I don't trust it with the engine. I've been looking at Bosch external pumps that supply twice the volume of fuel at the 70-ish PSI fuel pressure the Walbro is choking at, at a lower cost. Can anyone with experience of the Bosch pumps confirm whether they actually flow anywhere near their advertised 200LPH@5 bar?

As always cheers for any advice

-AJ

[cdwood2010]

Stupid question first, but I'm assuming its running full power, ie with the resistor removed / bypassed? Sorry I had to ask.

I fitted a Deatch works or whatever it called instead following some good reviews and recommendations. It started arsing about, and it had me looking for issues elsewhere until the stupid thing died.

So don't buy one of those.

At present I'm running on a jag v12 pump for moving it around. That seems to work OK.

C.

[AlunJ]

Hmm the pump should have been running full power. I was feeding the fuel pump 12v directly via the diagnostic socket for the tests and iirc that bypasses the resistor (plus helps avoid the "whoops spilled fuel on hot manifold" scenario). Shall have another look tomorrow though cheers

[Jiff Lemon]

hang on a mo..... if we're measuring flow at the return, isn't a restriction of flow good? Restricting the flow would increase the pressure on the other side wouldn't it? I.e on the inlet side

[AlunJ]

Yes, it's the restriction of flow that provides the fuel pressure in the rail. However according to it's spec sheet the walbro pump should be flowing nearly 200lph through the rail (and thus back down the return when injectors aren't firing) when the FPR restriction gives 70psi of rail pressure (which is our fuel pressure at 1.7 bar boost). I'm seeing just over a third of that.

[Goldy]

Have you checked the pressures measured are correct? What are you using to measure the fuel pressure?

Also for sizing have a look at :

http://www.deatschwerks.com/resource...ump-calculator

[AlunJ]

Yes, and there's no reason to doubt the accuracy of the fuel pressure gauge.
DW calculator specifies 192LPH @ 70psi for the injectors & boost pressure we're running. So again about 3 times what the walbro is delivering.

[AlunJ]

After a couple of hours tinkering I had a revelation. I am a moron

We've an engine making 370-odd horsepower at 1.1 bar. The turbo's sweet spot is 1.7 bar. We're putting in a set of cams whilst it's here. We've a nitrous system currently set up for 50 horsepower but capable of nearer 125. Even if my measurements are wrong and the walbro is flowing enough fuel and can run 500 horsepower there's an issue - it can only fuel 500 horsepower. This is an issue that I've never even considered. If it's not the issue now it most certainly will be once setup is complete and it has the inevitable balls-to-the-wall run for peak numbers.

I think a couple of high pressure externals used with a swirl pot are practically mandatory at this point. Walboro would be usable as a lift pump for the swirl pot (it seems to be happy in a high-volume low-flow situation) and it's cheaper than spending on a single in-tank pump that'll do the job. The single most fatal thing that could happen to that engine is it run lean on the gas. Nitrous assisted detonation is nasty and the Apexi Power FC running everything doesn't have any ability to compensate for det. I'd rather err on the side of caution than risk blowing the thing to pieces.