Swapping in walbro 255. Retune?
 

So, i am putting in a walbro 255 tonight. My stock pump is weak. I am pushing 14ish PSI on my disco potato and running over 90% duty cycle on my 550cc injectors. Once i put in this new pump, I will obviously have to retune my fuel map.
How would you guys do that? Would you go through and pull fuel every where or would you change the Req. Fuel number until it gets back to where it needs to be?

more than likely you'll have to retune.

Right, but can i just change the req fuel number and scale the whole map?

nope, going to have to retune. which is insanely easy with the ms.

indeed, a retune will be necessary.

the light load parts of your map will be just fine, the 255 wont actually supply any extra fuel to the engine as the pressure is controlled by the FPR.

the only parts you will need to retune are going to be in boost where the stock pump couldnt "keep up" with the pressure/flow demand of the engine.

Don't mess with the req fuel. It's used for a number of fuel calculations. Just retune your VE table. Use MLV.

I can see how going from a stock pump to a walbro 255 would require a re-tune. How about going from a 190 to a 255, same thing? Or even as a pump ages (how long do these walbro's last anyways?), would it fall off enough with age to make a noticeable difference?

A: It is commonly postulated (though I'm not sure I've ever seen proof) that the 255 flows such a large volume of fuel that the stock FPR cannot pass enough back through the return to maintain stock pressure at low load conditions. Thus, the pressure ratio across the injectors becomes somewhat non-linear, rather like the NB, and the injectors will tend to flow more. Fuel will need to be scaled back at the lower load portions of the map

B: The OP notes that his stock pump was "weak". If the pressure was dropping off at higher loads, then with the new pump pressure will be restored at the top end and the injectors will not have to work as hard. Fuel will need to be scaled back at the higher load portions of the map.


To the OP: Just do some logging and MLV analysis for a while. You'll probably be running a bit rich in places.

On the NA. The NB can use all the fuel you can give it, plus since the FPR is in-tank, you don't have the issue of heating up bypassed fuel.
I am a believer in 190hp for all NA and 255hp for all NB.

Yeah, I though that was kinda of inferred by the comparison I made that the NA started to act like the NB when this was done. :rolleyes:

Yeah.. well I guess reading that second sentence was way too much work for me. :dunno:
Anyway, at least it's clarified for the masses who do not understand Joe-Speak.