Yeah I think your getting the same issue. There's bound to be someone else with the same problem since most of us are using walbros nowadays. My rough idle could have easily been just a little bit of e85 on a 91 octane map that didn't get diluted yet with the 91 I just filled up with. I also found that at the exact moment the boost gauge finally does read vacuum like its supposed to, the walbro whine switches from a high pitched sound to a low pitched one, almost like it just got some load dropped on it, or it just finally started to cycle fuel... At any rate, I will keep this thread updated with any other observations I find later. I really should just get a fuel pressure gauge and shut up haha.

-Pal215

 

I have a DW301 fuel pump. If your pump is changing sounds though it's an electrical/ECU issue. The DW301 is too quiet for me to hear it change noises if it does.

 

If you were to have a fuel pressure gauge installed in your Evo, you would learn that usually these electrical in tank pumps such as the Wally start to show a slight loss of pressure only at WOT if and when they start to go bad.

That is, they don't go bad all at once, but instead at WOT they will start to deliver less fuel gradually over time. It is a very gradual, almost unnoticeable, loss of fuel pressure at WOT that is the telltale sign. And it is noticeable ONLY at WOT. Fuel pressure at part throttle and idle will still look normal.

The problem that you are describing however, is taking place at idle and at part throttle situations where there is a very low volume of fuel being consumed by the engine. Under these low fuel demand circumstances the pump is easily delivering more fuel to the rail than the engine can consume and the excess volume is being returned to the gas tank by the fuel pressure regulator. The pump is hardly working under the conditions where you are experiencing the problem.

So, for me it is difficult to see your problem as being strictly a fuel delivery issue caused by a faulty fuel pump. However, I am probably wrong. Alternately, the problem may have to do with the fact that as you mentioned, you have a dual fuel setup and perhaps when you switch over from one fuel to the other the low fuel maps and the high fuel maps are not properly configured to run on either one fuel or the other or a mixture of the two fuels. Or there hasn't been a complete and total elimination of one fuel or the other from the system.

Also, it might be a good idea to check the constancy of electrical voltage delivered at the pump at idle and at WOT. You could also switch to yet another WALBRO, or even go back to your old factory pump just to see if the problem persists.

 

hmm, i having a similar problem im getting a lopey idle and the vac reading i get at idle is is 10 or 11 hg but when im driving and on the throttle the car runs and feels fine first off thought it was a vac leak but i went over the system many times as well as a shop then moved on to think it was the egr or iac changed those and still same problem now im thinking its my fpr so ill change that and see how it goes if that dont work i dont know wth