05blue8

iTrader: (28)

I have a question and not sure where the real issue is. I have the Full Blown kit with the Buschur hobbs activation switch. One pump is wired to the stock wiring, the other to the Buschur hobbs switch. At idle the base fuel pressure is 40PSI, when I trigger the second pump at idle it's 50PSI. Isn't this too low? I searched but couldn't find the fuel pressure with both pumps running at idle...I thought it was supposed to be 75PSI? I've also tried swapping power from pump 1 to pump 2 and they behave the same. One pump on = 40PSI, secondary pump on 50PSI.

Thanks guys!
Matt

Ted B

iTrader: (6)

Step back and take a deep breath, because I'm here to tell you that you've come to the wrong planet.

The purpose of the twin in-tank pumps is to increase volume, not pressure. The notion that the FP at idle should be 75psi is incorrect. The reason why the pressure rises when you trigger the second pump at idle is because the added volume is overrunning the return system when the fuel demand is low. Simply put, the return system cannot vent the excess volume, which inadvertently creates a backlog of pressure within the fuel rail. The purpose of the Hobbs switch is to prevent that from happening, by triggering the second pump only when the engine is under boost.

At idle with the vacuum line to the FPR disconnected, you should see about 43 psi (~3 bar) with one pump running. When the engine is under boost, the actual fuel rail pressure should be the base pressure (43psi) plus the intake manifold pressure. So, 20psi boost should register ~63psi of fuel pressure within the rail. That keeps the pressure across the injectors constant.

05blue8

iTrader: (28)

Thanks for the details Ted. I understand the base pressure plus manifold pressure rising rate deal so not sure honestly where I came up with 75PSI.

The reason I brought this up is because my tuner notified me that it "appears" as though only one pump is working. I told him what I saw i.e. base fuel pressure with 1 pump vs 2 pumps but figured I could get a quicker answer here.

I read threads where people said at idle with both pumps running and the stock siphon the car should die out due to being overrun but mine doesn't, it stumbles but runs. Is it possible the previous owner of the Full Blown drilled out the siphon which is why the car isn't getting overrun?

I'll ask my tuner how he came to that conclusion also. I guess in the mean time to make sure the secondary pump is activating I'll hook up an LED just to make sure temporarily. Thanks again for the assistance. Anything else I can do to make sure it's activating? I'm not sure what else I could do...at this point I can't see any bases I haven't covered.

Ted B

iTrader: (6)

If the pressure rises from 40psi to 50 psi at idle when you trigger the second pump, it's working, and definitely overrunning the return line. This is undesirable regardless of how well or poorly it runs at idle, but since you are using a Hobbs switch, the second pump won't be running at idle anyway. If you were running both pumps full time, that would require the siphon drilling procedure, and you'd see only a small bump in FP at idle.

05blue8

iTrader: (28)

Thanks Ted, this morning I hooked up an LED to check the power and it's working. I'll let my tuner know, thanks a ton!

sparky

iTrader: (1)

The LED idea is good. Whenever I have run a staged double pumper setup I have always wired an LED into the circuit and installed the LED into the gauge pod as near as possible to the boost gauge(actually I prefer an Autometer mini-shift light to an LED). This way the telltale will light up instantly when the secondary pump activates and you'll know exactly at what boost level that 2nd pump is kicking in. Also, this way it is easier to setup the secondary pump at any chosen boost level. Furthermore, you'll also know if anything were to go wrong with the Hobbes switch or the wiring.

For example, if you want the secondary pump activating at 17 PSI it is much easier to watch the telltale LED and the boost gauge while driving and then adjust the Hobbes switch's activation accordingly than it is to rev your engine out in the driveway and spool the turbo up to 17# while your car is parked.

Another good idea is having a fuel pressure gauge mounted in the car. If you are using a non permanently mounted gauge then you really only see FP at idle. What you want to know is FP at WOT and at high boost levels., on the fly. Whereas, if you were to have a FP gauge in cabin then you could have it mounted next to your boost gauge and the pump's telltale LED. With a FP gauge so mounted you would notice that when the secondary pump activates the FP needle will jump momentarily due to the increase in fuel volume raising pressure at the rail before the FPR can compensate for the added volume. This jump of the needle lets you know for sure that the secondary pump is activating.

Another benefit of the in cabin FP gauge iinstall is that it will keep you informed as to the overall health of your fuel pump(s ). Walbros are not famous for their longevity. But, by watching your FP gauge over time you will know when either one, or both of your pumps starts to fail as you will see a gradual drop in WOT fuel pressure. over time

05blue8

iTrader: (28)

The Buschur hobbs switch is really prewired and everything. I'm seeing my second pump activated at 4PSI based on the LED light. I'll probably end up ordering the AEM FP gauge this week as another bit of insurance. I found out pretty quickly that my 40k old walbro was having output issues when I swapped just the double pumper with one pump from old to new and saw a full point drop in AFR. Thanks for the suggestion, AEM gauge it is

High_PSI

iTrader: (50)

At what WHP would a double pumper be needed? Can we get away with a single 255 Pump on a Black and Pump gas?

Spec-Ops1

iTrader: (38)

depends on your injectors and the amount of boost you are running. Honestly, for the boost you'd want to be running... you need the extra pump.

High_PSI

iTrader: (50)

So if I run say a Evo IX MR with a Black @ say 28-30PSI on 93 Octane with 1000CC injectors, I would need a double pumper?

Spec-Ops1

iTrader: (38)

I wouldnt say need, but you will be close to 90 to 95% maybe more on your injectors depending on weather i'd guess. With the double pumper, you'd be down to around 70 to 75, again guessing, but i bet im close.

EmeryatSTM

iTrader: (79)

On 1000cc injectors you will run out of fuel with a single pump at about 490 whp at 8k on our mustang dyno. The double pumper will get you to about 550 whp with that setup on our dyno.

-Em

High_PSI

iTrader: (50)

Hmm, this adds another $500 to the equation. DOes the unit over run the OEM FPR?

05blue8

iTrader: (28)

No it does not, Buschur has proven the stock FPR works great deep into the 9's.

Fast_Freddie

iTrader: (50)

Unless you are running both pumps at idle without drilling out the siphon, then it will overrun the FPR.