Stealth TDI
Pre-Forum Veteran Member
Hello,
Some of you may have read my "Dyno Letdown" topic in which I questioned the operation of my Walbro FRB-11. My troubleshooting compelled me to install a fuel pressure gauge so I could see what the pump was actually doing. It is specified to flow 43-gph at 6-8 psi. After installing the fuel pressure gauge, I learned the pump was pressurizing the fuel line to 6 psi when I first turn on the key (N109 cycle). Once the car is started, pressure hangs out around 3 psi at idle. It's about 2 psi at 50 mph cruise and 1 psi at 80 mph. It drops to ZERO under anything more than casual acceleration. I thought it was safe to say the pump was not delivering enough fuel to keep the feed pressurized under all conditions.
Tonight, I installed a brand new FRB-5. It's specified to flow 45-gph at 8-11 psi. They seem to be a popular upgrade (add-on?) for the Duramax folks. I got everything installed and hooked up. When the key is turned, the pressure jumps to about 5-psi and slowly climbs to 7-psi. Pressure drops to 3-psi at idle. In short, the pump behaves quite similarly to the FRB-11. The good news is my FRB-11 is fine. The bad news is either these pumps don't do what they're supposed to or I don't understand the external influences on these pumps (likely the latter).
I've been told, "get a PD lift pump," "get a Carter," "your pump is bad..." I suspect the majority of us read the specs of a given pump and accept that is what the pump is doing. But I'd like to request something a bit more scientific:
I'd like the input of those who actually have a fuel pressure gauge installed. Please post what lift pump you use, where your pressure is sampled, and what your pressure is just prior to start-up, at idle, and under acceleration. Perhaps a format like my example here:
Pump: FRB-5
Pressure sampled between the fuel filter and the IP
Pre-start: 6-psi
Idle: 3-psi
Acceleration: 0-psi (unknown if this is "zero" or vacuum since there is a mechanical stop... but IP timing is fine)
I don't mind a few theories of how pumps work and why my pressure reads what it reads. But please don't jump to the conclusion that I have the "wrong pump" or another "bad one" off the shelf unless you have a lift pump which maintains its specified pressure under all conditions and you have a fuel pressure gauge installed to prove it (meaning you understand how lift pumps behave in our application with fuel returning to the tank).
While I understand my topic is diagnostic in nature, I opted to post it in the Power Enhancements section due to the fact lift pumps are a popular power enhancement and my goal is to learn what the lift pump is actually doing (is it really providing "pressure" to the IP, or just ensuring there's not vacuum?). Others stand to learn something as well since I'm sure the vast majority of drivers do not have a fuel pressure gauge installed. Of course, moderators are welcome to move this at their discretion.
Thanks,
Scott
Some of you may have read my "Dyno Letdown" topic in which I questioned the operation of my Walbro FRB-11. My troubleshooting compelled me to install a fuel pressure gauge so I could see what the pump was actually doing. It is specified to flow 43-gph at 6-8 psi. After installing the fuel pressure gauge, I learned the pump was pressurizing the fuel line to 6 psi when I first turn on the key (N109 cycle). Once the car is started, pressure hangs out around 3 psi at idle. It's about 2 psi at 50 mph cruise and 1 psi at 80 mph. It drops to ZERO under anything more than casual acceleration. I thought it was safe to say the pump was not delivering enough fuel to keep the feed pressurized under all conditions.
Tonight, I installed a brand new FRB-5. It's specified to flow 45-gph at 8-11 psi. They seem to be a popular upgrade (add-on?) for the Duramax folks. I got everything installed and hooked up. When the key is turned, the pressure jumps to about 5-psi and slowly climbs to 7-psi. Pressure drops to 3-psi at idle. In short, the pump behaves quite similarly to the FRB-11. The good news is my FRB-11 is fine. The bad news is either these pumps don't do what they're supposed to or I don't understand the external influences on these pumps (likely the latter).
I've been told, "get a PD lift pump," "get a Carter," "your pump is bad..." I suspect the majority of us read the specs of a given pump and accept that is what the pump is doing. But I'd like to request something a bit more scientific:
I'd like the input of those who actually have a fuel pressure gauge installed. Please post what lift pump you use, where your pressure is sampled, and what your pressure is just prior to start-up, at idle, and under acceleration. Perhaps a format like my example here:
Pump: FRB-5
Pressure sampled between the fuel filter and the IP
Pre-start: 6-psi
Idle: 3-psi
Acceleration: 0-psi (unknown if this is "zero" or vacuum since there is a mechanical stop... but IP timing is fine)
I don't mind a few theories of how pumps work and why my pressure reads what it reads. But please don't jump to the conclusion that I have the "wrong pump" or another "bad one" off the shelf unless you have a lift pump which maintains its specified pressure under all conditions and you have a fuel pressure gauge installed to prove it (meaning you understand how lift pumps behave in our application with fuel returning to the tank).
While I understand my topic is diagnostic in nature, I opted to post it in the Power Enhancements section due to the fact lift pumps are a popular power enhancement and my goal is to learn what the lift pump is actually doing (is it really providing "pressure" to the IP, or just ensuring there's not vacuum?). Others stand to learn something as well since I'm sure the vast majority of drivers do not have a fuel pressure gauge installed. Of course, moderators are welcome to move this at their discretion.
Thanks,
Scott