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Fuel pump options for Turbo NNBS? Tuning FPCM?

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Old 05-29-2016, 06:03 PM   #11
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Having said all that, I did the walbro 450 pump before I figured all this out. So I can't say how far a stock flex fuel pump can go with this fpcm modification. I presume it would work fine until you made enough power that the stock 3/8" feed line would be a restriction before the pump would. But I do know that because of the restrictions in the stock bucket assembly, putting a 450 in place of the stock pump doesn't net you the full volume a 450 can supply. I've read that the stock bucket is only capable of somewhere between a 255 and a 340 pump. Either way, a 450 pump is cheap and easy to adapt into the stock bucket retaining all the stock bucket features. So it's cheap insurance so to speak.
Also worth mentioning, if you simply install the fpcm programmed as a cts v, you will have a check engine light on. You have to update your tune with the cts v data mentioned above to function properly with no check engine light.
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Old 05-29-2016, 07:38 PM   #12
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Any idea what duty cycle the stock pump is running at and what duty cycle the CTSV fpcm raises it to?
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Old 05-29-2016, 09:04 PM   #13
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My truck has always shown 99.6% duty cycle regardless of what pump or fpcm has been installed. I assume because it's a fixed style pump, not variable. Which doesn't make sense to me since I know it's pwm and obviously I'm driving it harder now. But if I set it as variable in the tune, it doesn't make over 34psi
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Old 05-31-2016, 09:40 AM   #14
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So whats the benefit of doing this mod? Do you have any measured gains of doing this over a stock setup or a stock FPCM with the 450 pump?

In theory, wouldn't the stock truck FPCM just increase the duty cycle of the pump until it meets the pressure demands? Because the fuel system does not monitor flow, only pulse-width and fuel pressure, all it can do is increase the pulse width until its at 100%.

Changing the FPCM wont give the fuel pump any more capacity, unless of course it operates at a higher voltage than the truck system does, which I am not sure if it does or not. If its at the same voltage, 100% duty cycle from a truck FPCM will deliver the same amount of fuel as 100% DC from a CTS-V FPCM.
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Old 05-31-2016, 10:20 AM   #15
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Quote:
Originally Posted by gravedigger472 View Post
So whats the benefit of doing this mod? Do you have any measured gains of doing this over a stock setup or a stock FPCM with the 450 pump?

In theory, wouldn't the stock truck FPCM just increase the duty cycle of the pump until it meets the pressure demands? Because the fuel system does not monitor flow, only pulse-width and fuel pressure, all it can do is increase the pulse width until its at 100%.

Changing the FPCM wont give the fuel pump any more capacity, unless of course it operates at a higher voltage than the truck system does, which I am not sure if it does or not. If its at the same voltage, 100% duty cycle from a truck FPCM will deliver the same amount of fuel as 100% DC from a CTS-V FPCM.
I think the CTS-V FPCM is only important to set your pressure based on above atmospheric boost reference. That would also require you having a different MAP sensor and the cal setup that way though.
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Old 05-31-2016, 01:04 PM   #16
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Quote:
Originally Posted by gravedigger472 View Post
So whats the benefit of doing this mod? Do you have any measured gains of doing this over a stock setup or a stock FPCM with the 450 pump?

In theory, wouldn't the stock truck FPCM just increase the duty cycle of the pump until it meets the pressure demands? Because the fuel system does not monitor flow, only pulse-width and fuel pressure, all it can do is increase the pulse width until its at 100%.

Changing the FPCM wont give the fuel pump any more capacity, unless of course it operates at a higher voltage than the truck system does, which I am not sure if it does or not. If its at the same voltage, 100% duty cycle from a truck FPCM will deliver the same amount of fuel as 100% DC from a CTS-V FPCM.
I can 100% for certain verify you will never get the amount of fuel with any pump and stock fpcm as you will with this mod. Most people looking into this are boosted and therefore already have a 2 or 3 bar map setup
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Old 05-31-2016, 01:06 PM   #17
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Plain and simple, it increases fuel pump output well beyond what the stock control module will with any tuning. Period
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Old 05-31-2016, 01:08 PM   #18
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Not doubting what you are saying, I am just curious what is does electrically to drive the factory pump harder.

I want to understand why it works
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Old 05-31-2016, 05:49 PM   #19
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Originally Posted by gravedigger472 View Post
Not doubting what you are saying, I am just curious what is does electrically to drive the factory pump harder.

I want to understand why it works
That is a mystery to me as well, because with both fpcm's, the duty cycle stays at 99.6% since it's a fixed pump setup. The only thing I can think of is that it increases the voltage that the pwm frequency cycles around. Sort of like an o2 switchpoint. Because the fuel system min voltage table is changed in the cts v cal. I'm tempted to back probe my pump connector and log hertz with my dmm just to see, but honestly, it works, som I'm leaving it alone. I did try setring the tune as a variable pump since the walbro is pwm capable, but the duty cycle stayed low and it didn't build much pressure.
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Old 08-09-2017, 07:14 AM   #20
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Yes, I was the one that figured it out and posted on a few different forums. The key is that the stock 5.3 fpcm sometimes doesnt accept a cts-v vin. Here is what i found to work and this is the only way.
Buy the fpcm for a 2009 Sierra Denali, i can get the part number off mine
Have a dealer or capable shop program a 2009 cts v vin into the module
compare your tune file to a 2009 cts v file. Under the fuel system tab in hpt, copy and paste everything different. then go under the system and voltage tab and copy the fuel system min voltage table.
now, the 09 cts v has the low flow pressure set to 36psi. however, all 2010-up cts have this set to 50psi. Its ok to go ahead and change this to 50.8 psi.
Now your truck will use the calculations and fuel pressure sensor to "crank the pump up" under higher flow conditions. This wont hurt anything or affect the tune as the ecm will adjust pulse width by fuel pressure.

This will take you a little farther. Once the stock pump is run out, tear apart the fuel pump bucket and put a walbro 450 in it.

My truck has this done with a walbro 450 in an absolutely otherwise stock fuel system, and i have 50-60 psi cruising and moderate throttle, then 70-80psi once boost starts really coming on. The increase in pressure is nice as it makes your injectors run bigger. I have 2013 ford mustang gt500 injectors and i havent hit injector or pump limit yet experimenting with 12psi of boost up to 65% ethanol fuel. Working towards full e85 and a maximum of 14psi boost
will this work on all nnbs cuz I have a 08 Sierra
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