DSX Low Side Causing High Side Pressure to Drop?

[67john98]

I just installed the DSX Low Side system on my 2017 Z06. Pump definitely works and turns on as soon Fuel Mode hits "High Flow". Now the low pressure looks great, it's the high pressure that's the problem. I'm running E30, just like I was before the added pump and high side would stay pretty close to the desired pressure under full throttle. Now the high side pressure drops to 1,000 psi (even 800 sometimes). AFR (Lambda) is constant at around 0.82 at full throttle even though the high side pressure is really low. I've only done limited runs on the street in 2nd and then in 4th gear. As soon as it goes into "High Flow" mode, the requested low side pressure jumps to 73 psi and the aux pumps turns on. Low side pressure jumps to 86 psi or so, confirming pump operation. At the same time high side pressure begins to drop. After 1.5s in High Flow mode, the high side pressure is right at 1,000psi and low side has dropped to 76 psi. That's as far as I went before letting off the gas (4th gear (auto), 5,000 rpm, 96 mph). Lambda solid at 0.83. Injector Pulse Width is quite a bit higher than previously. It's up to 10-11 when the aux pump kicks on. Didn't change anything else, so this is a real mystery. Any help would be appreciated.

Has anyone seen similar results? High side pressure being that low is pretty scary, but at the same time AFR is still good.

For Completeness here are the mods on the car:

Headers, off-road X-Pipe (no cats), stock mufflers
15% over-size lower pulley
Ported Throttle Body
Cold Air Intake
DSX Flex Fuel Sensor
DSX Low Side Pump and Controller

[67john98]

So I decided to set High Flow pressure to 499 kpa so the low side pump wouldn't turn on (supposed to activate when low side pressure is set to 500 kpa). That was all I changed in the tune. Flashed the ECM and check engine light as on afterwards. Drove around the block and noticed car indicated it was in 4th gear all the time, putting in Drive and it said it was in 4th gear. Put it in Manual mode and always in 4th, shifting did nothing. Something must be wrong with what I did so I flashed the previous tune and things got much much worse. Car would barely run and had many DTC codes. One bank had no fuel injection (PW 0). Tried to flash an even older tune and things stayed bad.

Walked home (about a mile), got a couple of tools and drove back. Disconnected battery and shorted positive and negative leads together for 10 minutes. Reconnected and all was good. Put new tune (not the one with fuel pressure changes) and it works fine. Now I'm afraid to change the fuel pressure thinking it could have caused the problems, but I also think somehow the ECM got confused and really needed the cold boot to get unconfused. Attached are both tunes and a short log from when it was running really bad.

Anybody go through this before?

[Joshinator99]

Running at WOT with injector PW in the 10-11 range means you’re going to be buying new pistons soon... 6 ms is the highest you want to see.

Sounds like you need a cam with a bigger fuel lobe to get the HPFP to keep up.

[HeavyChevy305]

With those mods your high side should be holding fine with e30. Did you change anything in the tune after you installed the low side?

[str8dum1]

I have a walbro 485 intank and the LT4 HPFP with LT4 injectors and see the same. Before I swapped the lowside, the high side would maintain fuel pressure while the low side dropped. So obviously upgraded the low side. Now the low side holds 100% but the high side drops. No changes to boost/ how much power the truck is making.

With all the forums saying that double and triple intanks will let a stock l83 HPFP make 700 whp, based on my experience, no way you need more low side than a single pump..

[Brianw36]

Has anyone else dealt with this issue? Is there a fix for this?