Walbro pump and nothing else

[p2motorsportmr2]

I have installed a walbro pump to my other wise stock fuel system, wolfkatz chart shows that there is a huge pressure drop with inj. open and closed is this a problem? Did i actually lose performance by installing a bigger fuel pump?
I have a stock turbo and downpipe, with greddy intercooler, intake, apexi ebc, and a 3" exhuast.

[Weasy2k]

See below :P

[Enthalpy]

Actually, I'm going to disagree. Something does happen, but what's up for debate is the severity of that thing. I'll explain.

The issue is the volume of fuel you are putting through the rail at stock pressures. That volume associated with the bigger pump creates a pressure drop across the rail. It's impossible for a stock regulator to fix that.

So what happens is one injector sees more pressure and overfuels that cylinder.

Because of where the regulator is, you won't UNDER-fuel any cylinder, but some will be grossly over-fueled. This will cause carbon buildup at an accelerated rate.

It bothered me enough to get a Wolfkatz rail for my car, even back when I ran 440s.

[5FistsoftheNorthStar]

Would I need to change much other than my regulator if I have a Gen3 engine?

[Weasy2k]

Originally Posted by Enthalpy

Actually, I'm going to disagree. Something does happen, but what's up for debate is the severity of that thing. I'll explain.

The issue is the volume of fuel you are putting through the rail at stock pressures. That volume associated with the bigger pump creates a pressure drop across the rail. It's impossible for a stock regulator to fix that.

So what happens is one injector sees more pressure and overfuels that cylinder.

Because of where the regulator is, you won't UNDER-fuel any cylinder, but some will be grossly over-fueled. This will cause carbon buildup at an accelerated rate.

It bothered me enough to get a Wolfkatz rail for my car, even back when I ran 440s.

ahh i take that back then...would it be sever enough tho?

Would a heat build up of sorts occur?

Being a hydraulics person i like to learn the technical crap too :P

[Enthalpy]

Originally Posted by Weasy2k

ahh i take that back then...would it be sever enough tho?

Would a heat build up of sorts occur?

Being a hydraulics person i like to learn the technical crap too :P

The regulator guarantees injector 4 is properly pressurized. Because of the pressure drop issue, that means injector 1 is over-pressurized at the high output volume of the walbro. This means cylinder 1 is overfueled the worst, and the overfueling decreases as you traverse the fuel rail.

When boosting, the closed-loop system isn't active, so cylinder 1 will be overfueled, which can lead to carbon buildup over time and increase the compression ratio.

When not boosting, the closed-loop system sees the overfueled condition across all cylinders and pulls fuel from all cylinders. This means 1 still runs slightly rich, and 4 runs slightly lean.

This last part is what I wonder about. Toyota chose the point at which the ECU comes out of closed-loop assuming the cylinders were fairly evenly-fueled. Now that 4 is slightly lean, is this a problem? Does allowing slightly lean operation right before the point where the ECU starts dumping fuel create the potential for detonation?

I don't honestly know. Personally, I got a Wolfkatz rail so I wouldn't have to answer this question.

Originally Posted by MR. 2Lanes

Would I need to change much other than my regulator if I have a Gen3 engine?

All indications I have seen to date seem to point to the fact that this issue isn't present in the already-larger gen 3 fuel rail.

[Weasy2k]

crazy thanks for the detail!

[p2motorsportmr2]

So if i get a bigger fuel rail the pressure will be more evenly distributed to all inj.? So will all the inj. being running rich with the larger rail or will it run closer to stock a/f?

[Matt94MR2]

Originally Posted by MR. 2Lanes

Would I need to change much other than my regulator if I have a Gen3 engine?

According to Wolfkatz the Gen3 fuel rail doesn't suffer these issues . I'm running a Walbro 255lph on my stock Gen3 fuel system btw.

[Enthalpy]

Originally Posted by p2motorsportmr2

So if i get a bigger fuel rail the pressure will be more evenly distributed to all inj.? So will all the inj. being running rich with the larger rail or will it run closer to stock a/f?

All injectors will operate at stock AFR.

[p2motorsportmr2]

well I ordered a ats rail. I'm probably going to need the extra fuel capacity eventually.

An unrelated question:

when i put the new rail in i was going to put my mat sensor in from the SDR ems as well. How much will removing the cold start injector effect my cold starting with the stock ecu?
It is probably going to be awhile before i can run and tune the SDR, should I just wait?

[Enthalpy]

Your cold start will be a little harder, but not impossible. After the engine is started and you release the key from the "start" position, there is no difference. Warm starts shouldn't be much different at all.

I actually have a customer right now that is going to run the Nemesis, but until he gets his 550s in, he's running the stock ECU without the cold start injector. As long as you can put up with a little harder starts in the morning, I wouldn't worry too much about it.

FYI - The ATS rail wasn't tested with the WolfKatz rail. I have no idea why, but it's therefore not guaranteed to fix the pressure drop issue. That said, I would guess it probably does fix the problem, given what ATS does to it.

[p2motorsportmr2]

thanks for all these great responses! they have helped me alot.