Question about FPCM Max Voltage with JMS booster

travislambert · 07-04-2020, 03:11 PM

Does anyone know the maximum voltage the FPCM will tolerate? I have a JMS voltage booster and seeing dips on the fuel pressure once the fuel level falls below 1/2 tank (because of the dang saddle tank design).

I'm maxing out at 17.1 volts right now without issue. I'm want to turn it up, but I'm at VIR at the moment and don't want to end up having to get towed.

The second part of my question is what happens with the FPCM is no longer happy? Does the car go into limp mode, just a MIL light, or what?

A quick response would be appreciated. I'm at the track now and have another day scheduled for tomorrow.

*Joshinator99* · 07-04-2020, 08:35 PM

Quote:

Originally Posted by travislambert

Does anyone know the maximum voltage the FPCM will tolerate? I have a JMS voltage booster and seeing dips on the fuel pressure once the fuel level falls below 1/2 tank (because of the dang saddle tank design).

I'm maxing out at 17.1 volts right now without issue. I'm want to turn it up, but I'm at VIR at the moment and don't want to end up having to get towed.

The second part of my question is what happens with the FPCM is no longer happy? Does the car go into limp mode, just a MIL light, or what?

A quick response would be appreciated. I'm at the track now and have another day scheduled for tomorrow.

Believe it pops a fuse if you overdo it.

LiqTenExp · 07-04-2020, 09:03 PM

17.48 is what I saw in some install guides. I'm at 17.4V since February and no issues.

travislambert · 07-04-2020, 09:22 PM

Quote:

Originally Posted by LiqTenExp

17.48 is what I saw in some install guides. I'm at 17.4V since February and no issues.

Great to know! Thank you!

L78toLT1 · 07-05-2020, 10:17 AM

How much does your low side fall off at low fuel levels? My car will sometimes throw a low side CEL towards the end of a track day. I never connected this to low fuel levels, but that would certainly explain it. When I return from the track and log my fuel pressures, everything is fine, probably because the tank is full again.
I'm also curious about the max voltage the fpcm can tolerate. I set mine to whatever Ted Jannetty recommend, seems like it was around 16.5v but I can't say for sure, it's been a couple of years since I installed my JMS.

travislambert · 07-05-2020, 02:03 PM

Quote:

Originally Posted by L78toLT1

How much does your low side fall off at low fuel levels? My car will sometimes throw a low side CEL towards the end of a track day. I never connected this to low fuel levels, but that would certainly explain it. When I return from the track and log my fuel pressures, everything is fine, probably because the tank is full again.
I'm also curious about the max voltage the fpcm can tolerate. I set mine to whatever Ted Jannetty recommend, seems like it was around 16.5v but I can't say for sure, it's been a couple of years since I installed my JMS.

When the pressure goes, it usually drops all at once. Here's an example showing the fuel pressure drop with nearly 1/2 tank of fuel. As you can see from the tank sensors all of the fuel is in the left side of the saddle when it happens.

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I bumped mine to 17.445 volts this morning and so far I haven't seen any problematic drops in pressure.

L78toLT1 · 07-06-2020, 10:23 AM

You're not kidding about your fuel pressure dropping all at once! I didn't really pay attention to how the low side pump was plumbed when I swapped my in tank pump out for the LT4 part, but apparently the pump functions as a transfer pump as well as supplying fuel to the hpfp. I need to figure out how to log using the torque app on my phone in order to better understand what's happening with my car. I've only logged using HPTuners and my laptop at the dragstrip or on the street, it's a bit awkward on the track. Your post has me pretty much convinced that the CELs I get after three or four sessions on the track are related to the fuel level. It would almost be too good to be true if this can be mitigated by cranking up the JMS a bit. Please keep us updated on your findings.

travislambert · 07-06-2020, 11:26 AM

I just noticed the picture was cut off a bit. Anyway, the blue 0.8% is the fuel level in the right side of the tank.

Our low-side fuel system uses a dual jet-pump setup. It's very close to this:

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Name: saddle-style-fuel-tanks-21.jpg
Views: 364
Size: 106.5 KB

Anyway, I bumped up the voltage to 17.445 max and turned the high flow pressure to 500 kpa. I didn't experience any losses in fuel pressure even with no fuel in the right tank at WOT for long periods.

Just to provide a little extra margin later, I think I'll probably swap the supercharger pulley with something slightly larger than 90 mm to lower the peak boost some.

07-04-2020, 03:11 PM	#1
travislambert Drives: '17 ZL1 Join Date: Jul 2016 Location: Fairmont, WV Posts: 1,567	Question about FPCM Max Voltage with JMS booster Does anyone know the maximum voltage the FPCM will tolerate? I have a JMS voltage booster and seeing dips on the fuel pressure once the fuel level falls below 1/2 tank (because of the dang saddle tank design). I'm maxing out at 17.1 volts right now without issue. I'm want to turn it up, but I'm at VIR at the moment and don't want to end up having to get towed. The second part of my question is what happens with the FPCM is no longer happy? Does the car go into limp mode, just a MIL light, or what? A quick response would be appreciated. I'm at the track now and have another day scheduled for tomorrow.

07-04-2020, 09:03 PM	#3
LiqTenExp Drives: 2017 ZL1 Join Date: Jan 2017 Location: NJ Posts: 926	17.48 is what I saw in some install guides. I'm at 17.4V since February and no issues. __________________ 2017 Camaro ZL1 Coupe M6 (847whp Dynojet on 93)

07-05-2020, 10:17 AM	#5
L78toLT1 Drives: Hyper Blue 2016 2SS 6M Join Date: Sep 2017 Location: North Ga Posts: 1,810	How much does your low side fall off at low fuel levels? My car will sometimes throw a low side CEL towards the end of a track day. I never connected this to low fuel levels, but that would certainly explain it. When I return from the track and log my fuel pressures, everything is fine, probably because the tank is full again. I'm also curious about the max voltage the fpcm can tolerate. I set mine to whatever Ted Jannetty recommend, seems like it was around 16.5v but I can't say for sure, it's been a couple of years since I installed my JMS. __________________ Baby Blue 2016 Hyper Blue 2SS/6m/MRC/NPP/Silver Rally stripes/ZL1 wheels & brakes/GForce DS and axles/ZLE Cradle Bushings/FE4 ARB front & rear/SEMA Grill/Rotofab dry/95mm TB/Magnuson 2300/Full LT4 fuel system/JMS boost-a-pump/E85 Sensor/Ported CID heads from LME/Cammotion PD cam/Thompson Motorsports forged shortblock/catted Kooks 1 7/8 headers /JRE remote tuned

07-06-2020, 10:23 AM	#7
L78toLT1 Drives: Hyper Blue 2016 2SS 6M Join Date: Sep 2017 Location: North Ga Posts: 1,810	You're not kidding about your fuel pressure dropping all at once! I didn't really pay attention to how the low side pump was plumbed when I swapped my in tank pump out for the LT4 part, but apparently the pump functions as a transfer pump as well as supplying fuel to the hpfp. I need to figure out how to log using the torque app on my phone in order to better understand what's happening with my car. I've only logged using HPTuners and my laptop at the dragstrip or on the street, it's a bit awkward on the track. Your post has me pretty much convinced that the CELs I get after three or four sessions on the track are related to the fuel level. It would almost be too good to be true if this can be mitigated by cranking up the JMS a bit. Please keep us updated on your findings. __________________ Baby Blue 2016 Hyper Blue 2SS/6m/MRC/NPP/Silver Rally stripes/ZL1 wheels & brakes/GForce DS and axles/ZLE Cradle Bushings/FE4 ARB front & rear/SEMA Grill/Rotofab dry/95mm TB/Magnuson 2300/Full LT4 fuel system/JMS boost-a-pump/E85 Sensor/Ported CID heads from LME/Cammotion PD cam/Thompson Motorsports forged shortblock/catted Kooks 1 7/8 headers /JRE remote tuned

07-06-2020, 11:26 AM	#8
travislambert Drives: '17 ZL1 Join Date: Jul 2016 Location: Fairmont, WV Posts: 1,567	I just noticed the picture was cut off a bit. Anyway, the blue 0.8% is the fuel level in the right side of the tank. Our low-side fuel system uses a dual jet-pump setup. It's very close to this: Anyway, I bumped up the voltage to 17.445 max and turned the high flow pressure to 500 kpa. I didn't experience any losses in fuel pressure even with no fuel in the right tank at WOT for long periods. Just to provide a little extra margin later, I think I'll probably swap the supercharger pulley with something slightly larger than 90 mm to lower the peak boost some.

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