Fueling issue with 15psi Hobbs switch and full E85

whyzee125 · 04-18-2023, 11:27 AM

Hey guys,

I'm having a bit of a fueling issue and I'm wondering what you suggest for the best way to solve it.

My car is FBO with port injection on full e85. Custom Wedge tune peaking at 21psi tapering down to about 15 at redline. It's running a fuel it stage 3 (twin Walbro 450? I think) triggered by a 15psi Hobbs switch, which provides PLENTY of fueling for my needs when the switch is triggered. Below is a log showing my HPFP and LPFP pressures on a 3rd gear run.

https://datazap.me/u/whyzee125/e85-l...hargepipe-ofhg

The issue is occasionally in 4th-5th gear at high but not full throttle, it seems to run out of fuel for a second. I think what's happening is the boost drops below 15psi, causing the secondary LPFP to turn off briefly and the HPFP runs out of supply until the secondary pump kicks back on. I have an LED light in my cluster wired up to illuminate when the second pump is running. The few times this has happened, it's when that light goes out for a sec, the car will stutter and jerk for a second before recovering. It's only happened 2-3 times but I'd imagine that's very bad for the engine so I want to make sure it doesn't happen again.

If I keep my foot to the floor, the light stays illuminated and I have no fueling issues.

Ideally I want a BPM4 as this seems like the 'proper' fix but I can't get one right now. A few ideas I had:

1) Use a lower PSI Hobbs Switch
2) Switch to a larger single pump like a Walbro 530 and just ensure my EKP has active cooling (though I'm not positive what pumps my stage 3 has)
3) Back off my tune to require less fuel until I can get my hands on a BPM4
4) Other

Thanks in advance!

iqraceworks · 04-18-2023, 02:02 PM

So your twin stage 3 pump runs one pump normally, and then after 15psi boost the second pump kicks in? Is that how you have it set up?

First thing I would probably do is pull the pumps out and verify what you actually have in the tank.

I just took a look at your log.......I don't see anywhere where you LPFP pressure is dropping off to the point where you would have fueling issues. The lowest pressure I see on your log is 58psi, and that won't starve your HPFP. What am I missing?

whyzee125 · 04-18-2023, 02:27 PM

Quote:

Originally Posted by iqraceworks

So your twin stage 3 pump runs one pump normally, and then after 15psi boost the second pump kicks in? Is that how you have it set up?

First thing I would probably do is pull the pumps out and verify what you actually have in the tank.

I just took a look at your log.......I don't see anywhere where you LPFP pressure is dropping off to the point where you would have fueling issues. The lowest pressure I see on your log is 58psi, and that won't starve your HPFP. What am I missing?

Yep! One pump runs off the EKP and the other off the Hobbs switch. In that log, both pumps are firing once it hits 15psi so in that log everything is working as intended.

99% of the time this is fine, but a few times when under high load, high rpm, but medium boost, it seems to starve the HPFP for a sec when that second pump turns off for a sec. It's only done it a few times so I've never caught it on a log but I have found shadow codes after this happened. Unfortunately don't remember which ones.

I'll try to pull my LPFP this week and see if it says what pumps they are. It's an older fuel it stage 3 so I'm 85% sure that's twin 450's.

Yotaismygame · 04-18-2023, 02:56 PM

Why run a hobbs switch at all? I understand the idea behind only running one pump when two aren't needed but if you google running dual fuel pumps there a lot of people out there that prefer to just run both all the time. I'd rather eliminate a potential failure point personally.

whyzee125 · 04-19-2023, 08:29 AM

Quote:

Originally Posted by Yotaismygame

Why run a hobbs switch at all? I understand the idea behind only running one pump when two aren't needed but if you google running dual fuel pumps there a lot of people out there that prefer to just run both all the time. I'd rather eliminate a potential failure point personally.

Thanks for the reply. I love that idea but I assumed the DME would throw codes for having too much fuel pressure at idle. Maybe the EKP would regulate the one pump its controlling so that wouldn't be an issue?

Yotaismygame · 04-19-2023, 10:15 AM

Quote:

Originally Posted by whyzee125

Thanks for the reply. I love that idea but I assumed the DME would throw codes for having too much fuel pressure at idle. Maybe the EKP would regulate the one pump its controlling so that wouldn't be an issue?

I'm not all that familiar with the n54 fuel system. Is it a return style system? My statement was pretty general. In other worlds running two pumps all the time with a return style system isn't an issue at all. Just adds a little more heat to the fuel since its cycling through more often.

whyzee125 · 04-19-2023, 10:18 AM

Quote:

Originally Posted by Yotaismygame

I'm not all that familiar with the n54 fuel system. Is it a return style system? My statement was pretty general. In other worlds running two pumps all the time with a return style system isn't an issue at all. Just adds a little more heat to the fuel since its cycling through more often.

I'll do a little research. If I could in theory, keep the secondary pump running all the time and allow the EKP to modulate the 'main' pump as needed I would sort of be switching roles of the two pumps but that should work better than a Hobbs in theory. Thanks for the reply!

whyzee125 · 05-03-2023, 11:00 AM

Hey guys, anyone else got any solutions to this? It seems everyone running a Hobbs switch could potentially have this issue so I can't imagine I'm the only one who has experienced it. I really want the BPM4 but I'm afraid of this happening too many times and melting a piston or something.

kenhassen1 · 10-22-2023, 11:14 AM

I've been dealing with something like this myself now. I've read some people were able to have their tuner use the exhaust flap control to run the secondary pump, the tuner was able to change the mapping for exhaust flap to run the pump on rpm and torque. Seems legit makes a fuel pump controller that replaces your ekp and adds the ability to run a second pump based on throttle position. I'm having similar issues and trying to eliminate possible problems. Fuel pressure dropping to 43 psi on dual 450s at 28psi boost. I also think I may have air trapped in my port injection rail but I may be over thinking it.

kenhassen1 · 10-22-2023, 11:27 AM

Another thought, you could mount a simple nitrous pedal switch behind your accelerator at the correct spot to ground the relay. I much prefer the other options I mentioned but it's simple, cheap, and will work. I thought about using the kick down switch but that won't work for the manual folks.

kenhassen1 · 10-27-2023, 11:21 PM

To update this, I found my issue. I determined that the second pump was not turning on at all. Pulled the fuel pump assembly and found the wiring for the second pump burned and damage at the connections in the hat. This was a fuel it stage 3 setup.

kenhassen1 · 10-29-2023, 11:43 PM

A further update to help those in the future, I found on closer inspection that the awg going to the top hat for my second pump is 12awg, the wiring under the top hat to the pump is 14awg. Walbro specifies the wiring coming of the pump is 12 awg. This is probably fine for the stock controlled pump as voltage is varied on use but for a direct wire second pump it is potentially an issue. My solution is to replace this section of wire with the correct awg and add a cable grip into the top hat so the only connection that could be exposed will be either in the tank at the pump or under the seat in the car.

04-18-2023, 11:27 AM	#1
whyzee125 Brigadier General 1694 Rep 3,659 Posts Drives: Dinan stage 2 335i Join Date: Jul 2014 Location: Chattanooga Tn iTrader: (0)	Fueling issue with 15psi Hobbs switch and full E85 Hey guys, I'm having a bit of a fueling issue and I'm wondering what you suggest for the best way to solve it. My car is FBO with port injection on full e85. Custom Wedge tune peaking at 21psi tapering down to about 15 at redline. It's running a fuel it stage 3 (twin Walbro 450? I think) triggered by a 15psi Hobbs switch, which provides PLENTY of fueling for my needs when the switch is triggered. Below is a log showing my HPFP and LPFP pressures on a 3rd gear run. https://datazap.me/u/whyzee125/e85-l...hargepipe-ofhg The issue is occasionally in 4th-5th gear at high but not full throttle, it seems to run out of fuel for a second. I think what's happening is the boost drops below 15psi, causing the secondary LPFP to turn off briefly and the HPFP runs out of supply until the secondary pump kicks back on. I have an LED light in my cluster wired up to illuminate when the second pump is running. The few times this has happened, it's when that light goes out for a sec, the car will stutter and jerk for a second before recovering. It's only happened 2-3 times but I'd imagine that's very bad for the engine so I want to make sure it doesn't happen again. If I keep my foot to the floor, the light stays illuminated and I have no fueling issues. Ideally I want a BPM4 as this seems like the 'proper' fix but I can't get one right now. A few ideas I had: 1) Use a lower PSI Hobbs Switch 2) Switch to a larger single pump like a Walbro 530 and just ensure my EKP has active cooling (though I'm not positive what pumps my stage 3 has) 3) Back off my tune to require less fuel until I can get my hands on a BPM4 4) Other Thanks in advance! Last edited by whyzee125; 04-18-2023 at 01:17 PM..
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04-18-2023, 02:02 PM	#2
iqraceworks Brigadier General 2002 Rep 3,731 Posts Drives: 2007 335i Join Date: Aug 2019 Location: Missouri iTrader: (0)	So your twin stage 3 pump runs one pump normally, and then after 15psi boost the second pump kicks in? Is that how you have it set up? First thing I would probably do is pull the pumps out and verify what you actually have in the tank. I just took a look at your log.......I don't see anywhere where you LPFP pressure is dropping off to the point where you would have fueling issues. The lowest pressure I see on your log is 58psi, and that won't starve your HPFP. What am I missing? __________________ 2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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04-18-2023, 02:56 PM	#4
Yotaismygame Lieutenant 130 Rep 496 Posts Drives: 2008 335i e92 (Beam) Join Date: Nov 2020 Location: OR iTrader: (1)	Why run a hobbs switch at all? I understand the idea behind only running one pump when two aren't needed but if you google running dual fuel pumps there a lot of people out there that prefer to just run both all the time. I'd rather eliminate a potential failure point personally.
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05-03-2023, 11:00 AM	#8
whyzee125 Brigadier General 1694 Rep 3,659 Posts Drives: Dinan stage 2 335i Join Date: Jul 2014 Location: Chattanooga Tn iTrader: (0)	Hey guys, anyone else got any solutions to this? It seems everyone running a Hobbs switch could potentially have this issue so I can't imagine I'm the only one who has experienced it. I really want the BPM4 but I'm afraid of this happening too many times and melting a piston or something.
	Appreciate 0 Quote

10-22-2023, 11:14 AM	#9
kenhassen1 Enlisted Member 6 Rep 32 Posts Drives: 09 135i Join Date: May 2022 Location: Colorado iTrader: (0)	I've been dealing with something like this myself now. I've read some people were able to have their tuner use the exhaust flap control to run the secondary pump, the tuner was able to change the mapping for exhaust flap to run the pump on rpm and torque. Seems legit makes a fuel pump controller that replaces your ekp and adds the ability to run a second pump based on throttle position. I'm having similar issues and trying to eliminate possible problems. Fuel pressure dropping to 43 psi on dual 450s at 28psi boost. I also think I may have air trapped in my port injection rail but I may be over thinking it.
	Appreciate 0 Quote

10-22-2023, 11:27 AM	#10
kenhassen1 Enlisted Member 6 Rep 32 Posts Drives: 09 135i Join Date: May 2022 Location: Colorado iTrader: (0)	Another thought, you could mount a simple nitrous pedal switch behind your accelerator at the correct spot to ground the relay. I much prefer the other options I mentioned but it's simple, cheap, and will work. I thought about using the kick down switch but that won't work for the manual folks.
	Appreciate 0 Quote

10-27-2023, 11:21 PM	#11
kenhassen1 Enlisted Member 6 Rep 32 Posts Drives: 09 135i Join Date: May 2022 Location: Colorado iTrader: (0)	To update this, I found my issue. I determined that the second pump was not turning on at all. Pulled the fuel pump assembly and found the wiring for the second pump burned and damage at the connections in the hat. This was a fuel it stage 3 setup.
	Appreciate 0 Quote

10-29-2023, 11:43 PM	#12
kenhassen1 Enlisted Member 6 Rep 32 Posts Drives: 09 135i Join Date: May 2022 Location: Colorado iTrader: (0)	A further update to help those in the future, I found on closer inspection that the awg going to the top hat for my second pump is 12awg, the wiring under the top hat to the pump is 14awg. Walbro specifies the wiring coming of the pump is 12 awg. This is probably fine for the stock controlled pump as voltage is varied on use but for a direct wire second pump it is potentially an issue. My solution is to replace this section of wire with the correct awg and add a cable grip into the top hat so the only connection that could be exposed will be either in the tank at the pump or under the seat in the car.
	Appreciate 0 Quote