hi i just fitted a walbro 255lhr fuel pump in my evo 4 the engine it running really lean and wont even boost properly it just misfires . i have a upgraded regulator and i cant get much pressure, but when i put the original pump back in it runs fine and i get up to 90psi. The walbro pump isnt the problem it works and flows fine so its something else, everytime the pump is put in it gets better as is more pressure but still not enough the fuel filter has been changed and got a little better but still no good, has anyone ever had this happen its really annoying me and have had to take it to a mechanic and they cant find the problem either its starting to cost me to much now. any ideas ???

 

It sounds like you've already isolated the problem to the regulator. Try swapping the stocker in and then using the walbro pump. While you're at it, learn how to use punctuation. Your post is very difficult to read.

 

Don't replace the stock fuelrail/regulator unless you are making over 600 HP. Make sure you have the correct pump. There are 2 types of 255 LPH Walbro pumps and one of them doesn't work with Evo.

 

I've got the same problem, and I think the problem is in the output length of the Walbro pump I've got. The black grommet and plastic clip wont stay at the tip of the fuel pump output. The grommet slides down the output when you push the fuel pump all the way into the housing, and I think the fuel is pushing back into the tank under heavy throttle application.
Is this thinking on track?

 

Anyone got pics of the two different fuel pumps or know what the differences are?

 

I agree with this line of thinking. The thread starter is most likely getting a bunch of fuel recirculation inside the gas tank, losing all his pressure in the connection between the fuel pump outlet and the cradle it sits in.

 

the difference in the two Walbro pumps is the orientation of the pump inlet to pump outlet. One pump has the inlet and outlet in a direct line on opposite ends of the pump, while the other has the inlet and outlet 180 degrees offset on opposite ends of the pump.