I haven't logged FP personally on an EVO but I suspect the walbro doesn't raise FP since you have an adequate fuel pressure regulator, it simply keeps it from going lower than 1:1

 

yeah sure, but it's not professional to let fuel trims handle it, it would be nicer to change injector scaling in this case.... (ie each time u d/c battery cables the ecu will hv to learn all over again...)
another reason im asking is in order to know injectors capacity. Say after you install the walbro, pressure rises from 43.5 to 47... this will mean injector capacity is now 47/43.5 * 560, right??

piece of information, fq 360 map raises injector scaling to 542, my guess is because they fitted a 255 walbro, thus raising pressure.
another evidence of higher fuel pres. when installing walbro pump is how afr's are dropping (as shown in some posts in this thread).

Plz lemme know abt my abv calc (47/43.5 * 560), would this be true given a 47 psi pressure??


thx again mate

 

the proper way to handle it is to install the walbro and adjust the fuel in the fuel map, not the injector scale unless you've installed upgraded injectors.

 

@Mellon: in this case why would afr's drop when installing walbro, even at low loads/rpms where standard fp can still cope?? and why would fq360 map re-scale injectors to 542??

 

bump

 

Adding the Walbro will increase your idle FP dramatically from 2.25 bar to nearly 3 bar. Your static pressure will stay the same though at 3 bar. The stock FPR does not have enough vacuum strength to adjust idle with the Walbro but the spring tension is enough to still control static pressure.

The problem people have with the walbro pump is the idle AFR's. Adjusting the fuel tables is useless because you are in closed loop mode (unless you modified your open loop settings so you could make adjustments at idle). Even with the evo's fuel pump circuit lowering voltage to the fuel pump to 8 volts at idle, it still overpowers the FPR's ability to control fuel pressure at idle. The narrowband O2 sensor will try to lower your fuel trims to achieve a 14.7:1 AFR but you might find the trims are maxed out and you still may not achieve a 14.7:1 AFR.

To completely control a Walbro pump you really should invest in an aftermarket adjustable FPR, this way you can mimic the stock fuel curve exactly. I am actually going to re-install my stock pump until I find that it is the one component holding me back.

 

I agree. The real solution would be to install an adjustable fuel pressure regulator that will not be overrun at idle, such as an Automotive.

No, you wouldn't adjust the injector scaling. This is because if the Walbro is over-running the stock FPR, it would only be at low fuel demand situation, like idle or low airflow. At higher airflows, enough fuel is being consumed where the return fuel is low enough not to overrun the stock FPR.

 

I believe he meant Aeromotive

THIS is the one I recommend. Cheap,easy to find and simple to install.

 

have you run into a car that couldn't trim enough fuel at idle? I haven't unless the injector scale was done wrong.

 

@l2r99gst : ic, so maybe fq 360 re-scaled injectors so that to control idle afr's, then changing fuel map values to get their desired afrs (at high loads/rpms).... nyway...

say i purchased an after market fpr, and set fuel pressure to 47 psi, would the right way to calculate injectors capacity be 47/43.5*560??
why isn't any1 answering this ?

 

Doh...Yes, I meant Aeromotive. Sometimes my thoughts are ahead of my typing.

 

I haven't looked at 360 maps, but your logic sounds like a possiblity.

The calcuation is the square root of the new base fuel pressure over the old base fuel pressure multiplied by the injector flow rate:


SQRT (47/43.5) * 560
=582

 

guess u forgot to take sqrt, o'wise would hv been 582....

 

Boy, I am making a lot of dumb mistakes today. Yes, 582 is the correct answer. I will fix the post above.


Eric