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