What are the results of having a walbro fuel pump, and no tune?

I am guessing bad gas milage, running rich, and possibly fouled spark plugs.

 

Bump

 

ttt

 

seriously 40 views and no one has any input?

 

nice avatar!

 

^^^True!

Those things you mentioned most likely. My advice...get tuned. I put mine in and I have no other mods besides a custom flash, just to be safe.

 

+1

seriously though I am also insterested. I would think there would be no ill effects. Just a wild guess though so dont take my word for it.

 

theoretically speaking,since I don't have first hand knowledge of the EVO's fuel pressure regulator's (FPR) capabilities, as long as the FPR can bypass the extra fuel the Walbro puts up and maintain stock fuel pressure settings, there will be no ill effects and no running rich. The FPR bypasses the most fuel when the fuel isn't being fed through the injectors, and the fuel recirculates back to the fuel tank. The EVO fuel pump (and the Walbro will do the same) operates at two different voltages, one for low engine load and one for high engine load, there will be two points when the FPR has to bypass the most fuel. Idle will be one point (lowest engine load in the "low" voltage mode), and the other point will be when the pump first kicks into high voltage mode (lowest engine load in the "high" voltage mode). All other points in the fuel map will have more fuel going through the injectors and less through the FPR, and it will be easier to maintain stock fuel pressures.

If you subscribe to Turbo Magizine, they did a nice writeup on fuel pumps in the 04/04 issue, and both the stock EVO pump and the Walbro pump were included. At typical idle fuel rail pressures (35 psi), the Walbro outflowed the stock pump by 31% at 13.5 volts. But since the voltage to the pump is reduced at idle (i.e. low voltage mode), it's hard to draw any conclusions from that. But more importantly, at full boost fuel pressures (55 psi or so since fuel pressure is raised # for # with boost pressure), when the pump is just kicking into high voltage mode, the Walbro outflowed the stocker by 53%. So the FPR will need to have the capacity to bypass an extra 53% over stock, or you will run rich. As the rpms rise, and fuel demands go up, the FPR regulator gets a break as more fuel flows through the injectors and less have to be bypassed. So there could be a window when you do go rich due to excess fuel pressure right around peak torque, but it will start to catch up as the hp numbers climb.

Some or all of this you may have already known, just trying to help.

 

I have the same question
Going to get my car tune by AL in a month and here are my current mods:

dp, catback, intake, hyper ground wires, mbc

now I'm looking to get a test pipe and fuel pump before the tune, with these two additional mods, would it be quite a gain than w/o them?

 

i did a test on this and posted dyno sheets for anyone who wants to do a search

Basically with a walbro pump your closed loop and low boost opeartion is the same as with the stock

On full boost on the upper rpms 5500 and above the car will run a bit richer with the walbro

The rational for changing the pump on a low power car is due to the greater consisteny and more reliable fuel supply in hot conditions

One you are tuned with or without the pump you dont want to change it with out changing the tune

The stock pump is good for about 320 whp before it starts to loose some pressure on the end of a long pull - the more power you make above that the more fuel pressure that falls down

At some point the injectors reach 100% duty cycle and you go lean as you make more power

With the Walbro you can go well over 350 whp with no loss in fuel pressure

hope that answers some of your questions