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FiTech Go EFI question

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16 minutes ago, Mike65 said:

Do you need the CC to run the FiTech efi?.

You need either CC or an electric high pressure fuel pump and a return line to tank, some people use FI tank with pump inside (like Spectre FI tank). Mechanical fuel pump does not provide necessary pressure for the injectors. Mechanical pump pumps gas into CC, and electrical pump inside CC pumps to injectors (58 psi I believe).

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Thanks for the link Vic, I read some of the questions & someone asked about the Spectra EFI fuel tank & FiTech recommended contacting Spectra about if the Spectra fuel pump will work with PWM system. I sent Spectra an E-Mail to see if the fuel pump in their EFI tanks will support PWM system, & I will post their response once I hear from them in case any one else is interested in going this route.

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9 hours ago, Mike65 said:

Thanks for the link Vic, I read some of the questions & someone asked about the Spectra EFI fuel tank & FiTech recommended contacting Spectra about if the Spectra fuel pump will work with PWM system. I sent Spectra an E-Mail to see if the fuel pump in their EFI tanks will support PWM system, & I will post their response once I hear from them in case any one else is interested in going this route.

I’m a bit confused Mike. If your running an in tank pump with a return line as I am you won’t be using the PWM. This is only needed when using the CC or a non return style set up. The PWM function is disabled from factory and you need to turn it on if required.

Mark

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57 minutes ago, Shep69 said:

I’m a bit confused Mike. If your running an in tank pump with a return line as I am you won’t be using the PWM. This is only needed when using the CC or a non return style set up. The PWM function is disabled from factory and you need to turn it on if required.

Mark

As I understand, you can use PWM to reduce the load on the tank pump during idle etc even you have a return line.

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51 minutes ago, aslanefe said:

As I understand, you can use PWM to reduce the load on the tank pump during idle etc even you have a return line.

Ok I wasn’t aware of that. I know that at idle and low rpm cruise when the pressure regulator is hooked up to the vacuum line it reduces the pressure . I think it’s around 43 psi instead of 58 psi. It’s meant to smooth out the idle. 

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 I may be wrong, but  It was my understanding that the way that the system controls the fuel pump is always through PWM  Technology.  So for external fuel pumps the setting would always be at the highest value.  One of the issues I’ve read about frequently is that for the fuel command center there have  been problems with overheating. FiTech  said  that their default PWM setting was always on high, designed to support external fuel pumps. So now they are changing their default setting to a lower value to support the FCC  to slow the pump down and reduce the amount of heat that’s generated . I haven’t checked to see what mine is but they have a recommended PWM value for the fuel command center, and a different one for external fuel pumps.  I mentioned that to Mike in an earlier response and that’s what started this chat about the PWM settings. I’ll go back and read up on this to see if I’m correct or not.  

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I asked about this on the FiTech FB page and one of the gurus Replied to me . This is what he said about my in tank pump setup . 

The thing is, once they build system pressure all the excess is returned so the load is constant. With pwm the motor is pulsated, starting and stopping hundreds of times a minute. That start load is harder on the motor than constantly running.

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I think since the FCC is designed to operate with no return line, the pump speed has to be varied to match the load of the engine, as opposed to the constant speed/constant flow set up with an in-tank pump, or a frame mounted pump with a return line.    So, I guess the best solution was the PWM.  The old school way would be to put a rheostat (big variable resistor) in line with the pump to control the speed.   This is very inefficient, and takes up a lot of space...     This same approach is used to control your blower motor speed on your Mustang.  Instead of a variable resistor, there are three pre-set resistance values for the three fan speeds.

All PWM does is vary the duty cycle of the motor.   If you directly wire the motor, it gets full voltage and current 100% of the time, so it has  100% duty cycle.   If you manually cycled the pump on for one second, and off for one second, you would have a 50% duty cycle.   With PWM, you can control the motor speed by varying the duty cycle down to the milli-second level.  This is done by generating a square wave form and varying the distance between the peaks to change the duty cycle.   The advantage of PWM is that it is very efficient, and does not dissipate much energy.  I have a PWM fan controller for this reason.  It does soft start, and varies the speed of my 2  - 12" fans that is proportional to the temperature input/demand.   It uses no relays.   

Shep makes a good point on the motor life.  I am not sure about that.  I believe the duty cycle is what impacts the motor life, but not certain......

I wonder what size the FiTech FCC fuel pump is...

I looked at some in tank pumps...

The real interesting thing is what fuel is really required.   From the Holley technical page:

FUEL REQUIREMENTS Typically, at wide open throttle, full power, an engine requires 0.5 lbs. of fuel per horsepower every hour. A gallon of gasoline weighs approximately 6 lbs. Therefore an engine rated at 350 horsepower will require about 175 pounds (29 gallons) of fuel every hour. (350HP x .5 lbs = 175 lbs of fuel )  

But, even looking at a big block Chevy mechanical fuel pump, it is sized around 170GPH.     

I did find some curves from AEM that show the relationship between flow, pressure, and current (flow and current are proportional, and inversely proportional to flow) for their high flow pump.  I think the relationship between the three would still be accurate for a pump with lower flow, but I could not find any better curves on line.  The one thing it does show is how much current these pumps really can draw.   The FiTech limit is 7 amps

Anyway, some fun research for a Saturday morning for me.   Headed down to the shop to finish my under dash wiring....

 

 

 

 

 

400lph_inline_Fuel-highflow_pump_vol-met-flow-current_vsPress_chart.jpg

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Nice work Vic. Make sure you have a spare pump on hand as I’ve heard that the FiTech Chinese ones don’t have a long life. Sad but true. Another thing I was told to do was to remove the regulator on the side and check it for debris. Plenty of people have had machine shavings in there. They are cheap enough to replace with quality ones. 

7B70A42F-4581-47CB-8786-1397643A2418.png

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