Dsx aux system fuel presure

[Blakester]

Considering doing a dsx system and a zl1 pump on my car. Just curious how pressure control works since the aux pump itself doesnt seem to be controlled by the fpcm and I assume it taps into the factory fuel line without any use of a regulator that comes in the kit. When the pump is working under boost what's controlling fuel presure?

[eLeSthree]

Fpcm. The system goes between the zl1 pump output and the feed line to the rails. It gets fuel from the tank and injects it into the feed line (tee’d) after the zl1 pump.

You still use the tune in the fpcm to command low/high flow modes.

[DSMer1]

The best strategy is to set the fpcm to a high commanded fuel pressure under boost so when the aux pump comes on the fpcm doesn't try to reduce the fuel pressure via pwm control of the stock pump. This is accomplished by telling the fpcm to command a higher pressure that the system will make, like 500kpa. That way it just runs the factory pump at full tilt (kinda) along with the aux pump. This strategy worked well for me.

[Blakester]

Thanks for the responses guys! but I'm still not seeing how fuel presure is kept under any control since the aux pump isn't controlled by the fpcm. Once it is fired it seems to me itll just run at what ever presure the aux pump is capable of flowing. Is there a relief in the aux pump itself? What kinds of pressures are you seeing on a long pull?

[Rem0v3r]

Doesnt it have a fuel pressure regulator and the excess is bled back to the fuel pumps feed line?

[eLeSthree]

Originally Posted by Blakester

Thanks for the responses guys! but I'm still not seeing how fuel presure is kept under any control since the aux pump isn't controlled by the fpcm. Once it is fired it seems to me itll just run at what ever presure the aux pump is capable of flowing. Is there a relief in the aux pump itself? What kinds of pressures are you seeing on a long pull?

I set my fpcm to command 80psi in High flow mode. Of course the zl1 pump cant deliver 80psi of 88% Ethanol to a 950 crank horsepower engine, but with the Aux pump, I'd see a spike to 80 and then taper off to 72ish. Now as the demand for fueling goes up, the pressure drops faster, especially with more boost working against you. At some point you may outgrow the system. You should see a new DSX product hit the market real soon, for those with major HP in mind.

It definately bridges the gap between a zl1/BAP/fpcm and a full on Fore Triple.

Originally Posted by Rem0v3r

Doesnt it have a fuel pressure regulator and the excess is bled back to the fuel pumps feed line?

No, the stock fpcm acts as the electronic fpr.

[DSMer1]

Originally Posted by Blakester

Thanks for the responses guys! but I'm still not seeing how fuel presure is kept under any control since the aux pump isn't controlled by the fpcm. Once it is fired it seems to me itll just run at what ever presure the aux pump is capable of flowing. Is there a relief in the aux pump itself? What kinds of pressures are you seeing on a long pull?

eLessthree above is spot on. Commanding something like 80psi in high flow is key. Even with the aux pump running the system won't make that much pressure so the fpcm will just run the factory pump full tilt. The way the factory ECU is setup with live pressure reporting to it, it compensates for lower than commanded pressure with higher injector duty cycles.

[Blown1LE]

I am have this exact same set up in my car and am having an issue with it and I wondered if it could be fpcm issues. The car falls flat on its face every now and then right around 3000 rpm and it seems to be shortly after the DSX pump kicks on I see the pressure raise up to about 80 psi and then then it will instantly drop to say 30 psi for a split second. It doesnt happen every time but I definitely dont trust the car to run it hard at lower rpm. It never seems to happen at higher rpm. The tuner I took it to originally had no idea the fpcm needed an update but I was able to get it remotely updated but something just isnt right, I took the car and had it retuned and due to the rpm range we were in during the runs we never saw the issue but now in daily driving the car falls flat on its face even during moderate acceleration and it always seems to be right around the same rpm range. I need to get the car back to my tuner as I am pretty sure it is something the original tuner did that is now popping up but is there anything mechanical I should be checking to rule that out ? Thanks

[Blakester]

Ok so the dsx pump is a pwm pump that is compatible with the stock fpcm once the module has been configured to run higher than stock pressures.

[Blakester]

And or under enough load, the fuel presure doesnt spike to some insane amount because there is enough demand

[Rem0v3r]

Can someone post their fscm tune for the aux pump.

[Rem0v3r]

So if i get this right... the zl1 pump behaves as normal.. the foot hits the floor, and when demand is high the aux pump kicks on.. at which time the zl1 pump was falling off anyways... the aux pump hits the system with a shit ton of fuel, and the zl1 pump eases off and either bleeda the extra pressure over commanded or makes up the difference to get to commanded..

Is that correct?

[eLeSthree]

Originally Posted by Blakester

Ok so the dsx pump is a pwm pump that is compatible with the stock fpcm once the module has been configured to run higher than stock pressures.

The fpcm doesnt control the dsx pump, the dsx controller is responsible for triggering the pump based off boost pressure. The fpcm tries to control the fuel pressure. With the standard dsx aux pump, as long as you’re not over taxing the system, you will get whatever you command in highflow mode. (80psi). I however was over working it, and seeing some pressure drop.

This forum does not allow you to post tune files.

How much power are you planning to make on which Power adder on which fuel?

[Rem0v3r]

Turbo, 10-12 psi, full e85, 1000cc injectors