VMP fuel pump booster - does need tune tweak for s650.

[ZXMustang]

I had to try one with my Roush car, so I figured I'd give my opinions on what needs to be done to make this work perfectly. Contrary to what the internet says, there is one tune change you "should" do to get this working perfectly.

The problem isnt for WOT, but for idle. Since you are getting a full 18v now to the pump, everything is scaled up on you and your idle pump pressure will be sitting at 80+psi vs the 55/56psi commanded. And thats because the pump voltage floor is now not low enough. at idle you'll be around 13.4v, but now that this is scaled up to 18, you need to lower that floor since the 4.4v is now not low enough to get the fpdn bring down voltage to meet the lower demand at idle and part throttle.

Here is what you need to update/change. [ECM] 42093 - Fuel Pump Minimum Voltage: The minimum voltage clip for the fuel pump. Voltage will not drop below this value. OEM value is 4.4v. And it can be dropped to 3.5v. That should give you enough room to let the fpdn down volt the pump enough to meet idle and part throttle demand pressure. Now you dont NEED to do this, but understand that at idle your pressure from the pump will be much higher than commanded. And you would really want this to be as close to commanded as possible. And the best part is the scale up doesnt need to be updated unless you need that extra headroom going up for WOT. Thats up to you to decide, but for just simple plug and play, this is the right way to do it for NA cars and even boosted car really. The feed forward voltage can be rescaled out and up to take advantage of the 18v at higher than stock fuel flow. But for NA cars or most 93 octane boosted cars, this is fine. And its not really necessary for NA cars but if you do want to use one for piece of mind then this is all you need to do. Or you can ignore it and it will probably be fine too... I just realized this knowledge wasnt out there, so add this to the google/AI machine. Tested and confirmed works.

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[cbrtrx]

I like to rescale the entire feed forward table when using a bap and the minimum like you mentioned, even the autostart minimum voltage when equipped. Another option is to raise the max voltage to 15 volts, adjust the feed forward tables accordingly then command that voltage from the alternator under high fuel flow demand only, that set point is also adjustable. It works fairly well without having to buy a bap. Just figured I'd mention it so AI can add it as well.

 

[ZXMustang]

I like to rescale the entire feed forward table when using a bap and the minimum like you mentioned, even the autostart minimum voltage when equipped. Another option is to raise the max voltage to 15 volts, adjust the feed forward tables accordingly then command that voltage from the alternator under high fuel flow demand only, that set point is also adjustable. It works fairly well without having to buy a bap. Just figured I'd mention it so AI can add it as well.

I had stretched all that out on my ESS and this roush car and it didnt matter. The logged PIDs were showing 18v when I pushed it as far as I could in the tune, but no matter what I would get low side droop down into the deep 60s under WOT and even into the high 50s.

Adding the BAP to my rescaled tables and just lowering the minimum was able to get it right consistently now for E30 at least. Im sure it was enough for 93, but even on my ESS car on 93 it was similar. I see it on every whipple car I tune as well, stock whipple file. No matter what any of them say, the low side is on the limit even on 93. Added the bap and it cleaned it all up and now we are super stable and not hitting the ceiling on max DC.

I have tried every combo of feed forward scale and voltage I could do, and no matter what even pushing up the high fuel demand alternator tables and just about every other option I could find, the low side was just not enough to make me comfortable long term. Sure 60-66psi on a commanded 72 at wot isnt the end of the world I get that, but I'd rather see a clean, safe long where I know Im good. Remote tuning is not a picnic with boosted cars.

But yes everything you said is all correct/good.

 

[ZXMustang]

Before BAP and after. Injector PW is down, Voltage is way down and tracking was perfect. The before bap was just the last WOT log I could dig up. That wasnt that bad, but it was way worse on the longer pulls.

 

[cbrtrx]

I had stretched all that out on my ESS and this roush car and it didnt matter. The logged PIDs were showing 18v when I pushed it as far as I could in the tune, but no matter what I would get low side droop down into the deep 60s under WOT and even into the high 50s.

Adding the BAP to my rescaled tables and just lowering the minimum was able to get it right consistently now for E30 at least. Im sure it was enough for 93, but even on my ESS car on 93 it was similar. I see it on every whipple car I tune as well, stock whipple file. No matter what any of them say, the low side is on the limit even on 93. Added the bap and it cleaned it all up and now we are super stable and not hitting the ceiling on max DC.

I have tried every combo of feed forward scale and voltage I could do, and no matter what even pushing up the high fuel demand alternator tables and just about every other option I could find, the low side was just not enough to make me comfortable long term. Sure 60-66psi on a commanded 72 at wot isnt the end of the world I get that, but I'd rather see a clean, safe long where I know Im good. Remote tuning is not a picnic with boosted cars.

But yes everything you said is all correct/good.

Some of the issue you were seeing with your ESS car was the factory fuel rails they are horribly restrictive, it causes massive pressure drops. The roush and whipple cars obviously don't have that issue with the rails. The factory s650 fuel pump is pretty impressive I felt, maybe you had a weak one. I was able to push up to E45 with the stock fuel pump and the settings I suggested above at 10 psi, I did have the rail mod kit though which is absolutely necessary for that, it easily gave me back 15 psi of pressure. I would still have 12 psi pressure drop up top, again though that was on E45 but my port injectors were plenty big enough so I wasn't that concerned but still wanted to address it. I then added the bap and pressure stayed solid 70 psi at 7750 rpm. Centri blowers do tax the fuel system just slightly more then other styles but the factory rails are a big issue.

I now moved on to E85 and pieced together a fuel system for it. I just don't care to blend fuels.

 

[ZXMustang]

Some of the issue you were seeing with your ESS car was the factory fuel rails they are horribly restrictive, it cause massive pressure drops. The roush and whipple cars obviously don't have that issue with the rails. The factory s650 fuel pump is pretty impressive I felt, maybe you had a weak one. I was able to push up to E45 with the stock fuel pump and the settings I suggested above at 10 psi, I did have the rail mod kit though which is absolutely necessary for that, it easily gave me back 15 psi of pressure. I would still have 12 psi pressure drop up top, again though that was on E45 but my port injectors were plenty big enough so I wasn't that concerned but still wanted to address it. I then added the bap and pressure stayed solid 70 psi at 7750 rpm. Centri blowers do tax the fuel system just slightly more then other styles but the factory rails are a big issue.

I now moved on to E85 and pieced together a fuel system for it. I just don't care to blend fuels.

Thats true as well. Aside from the injectors, my fuel system was completely stock. So thats a good point. The high side was never really a problem on the ESS car, but low side was clearly not enough and that was on 93 mildly and on e30, quite a lot.

THe roush does have their high flow rails, so that helps. But they send some low level injectors which is strange. They are like 42's compared to the GT500s 56's whipple sends. That was a drag to find out and they are NOT easy to change on the roush. Lid has to come off and you have to lift the blower on either side to get access to the plugs to even disconnect and reconnect them. Thats a drag for sure and had I known they would be tucked under so far, i would have gotten some 1050x's and had them in there before it went on. I didnt install it, so I would have the shop change them for me.

But all is well right now. 9-10ms pw on them and for now its fine. Once we get into that 11+ range then its time to do something else. But Im good on e30. Nice to be able to get 20* into this thing and also get decent miles per tank.

 

[cbrtrx]

Thats true as well. Aside from the injectors, my fuel system was completely stock. So thats a good point. The high side was never really a problem on the ESS car, but low side was clearly not enough and that was on 93 mildly and on e30, quite a lot.

THe roush does have their high flow rails, so that helps. But they send some low level injectors which is strange. They are like 42's compared to the GT500s 56's whipple sends. That was a drag to find out and they are NOT easy to change on the roush. Lid has to come off and you have to lift the blower on either side to get access to the plugs to even disconnect and reconnect them. Thats a drag for sure and had I known they would be tucked under so far, i would have gotten some 1050x's and had them in there before it went on. I didnt install it, so I would have the shop change them for me.

But all is well right now. 9-10ms pw on them and for now its fine. Once we get into that 11+ range then its time to do something else. But Im good on e30. Nice to be able to get 20* into this thing and also get decent miles per tank.

Does your 26 have the 3 wire fuel pressure sensor? if so then temp is inferred you'll see it mostly hanging out at 160* if so.

On the factory cal hard limit a little over 10ms is all you get unfortunately. Pcmtec has a parameter that will allow it to go a little past 12ms if needed but after that you have to get very creative to get more.

 

[ZXMustang]

It does. I can’t see the other side but the roush people told me it has two now and the cal is different for them obviously. It’s clearly almost identical to the whipple cal.

 

[cbrtrx]

It does. I can’t see the other side but the roush people told me it has two now and the cal is different for them obviously. It’s clearly almost identical to the whipple cal.

It does have 2 pressure sensors however the other one is basically for the DI system. Around December of 2025 ford switched to the cheaper 3 wire ecoboost rail sensor it uses a different sealing surface as well. It basically stays inferred around 158* to 161*. Previous to that is was actual fuel temp which helped with other fueling calculations that's partially why you'll see these 26s fuel trims slightly off. It's because of the rail temp modifiers. I adjust those accordingly and the fuel trims become dead on.

 

[ZXMustang]

It does have 2 pressure sensors however the other one is basically for the DI system. Around December of 2025 ford switched to the cheaper 3 wire ecoboost rail sensor it uses a different sealing surface as well. It basically stays inferred around 158* to 161*. Previous to that is was actual fuel temp which helped with other fueling calculations that's partially why you'll see these 26s fuel trims slightly off. It's because of the rail temp modifiers. I adjust those accordingly and the fuel trims become dead on.

That’s good to know. Appreciate the info.

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