Fuel pump control module

[frank_ster]

So what's the big deal about having a fuel pump that can be ramped down?

 

so the evaporative emissions don't flood the engine!

 

and i think they fear for life of the pump, thinking that a fuel pump would last at running at its designed speed. i would be worried if they bumped the pump up to 16 volts. but not at 12v.

 

and i personally dont care about either of those things and we both have stated our opinions.

 

mwiener imho your being a little to pushy in this particular thread, and i may be doing the same in other threads. but maybe take a few steps back and let these guys figure out what they want to learn for their own reasons.

[frank_ster]

I think we are going to replace the factory negative wire (from FP to FPCM) and see. It may be an issue of resistance running a large positive wire and a very small negative wire. We will report on the results.

 

well if a wire is very long it will need to be big if the wire is short it can get away with being smaller.

[KCwagon]

well if a wire is very long it will need to be big if the wire is short it can get away with being smaller.

 

The factory negative wire for the FPCM (16g) is about five feet long. The positive wire that we replaced is about the same length and is 12 gauge. From what I have read, the folks that replaced both the positive and negative wires from their FPCM have seen at least 13.5 volts. Giving it a try on Friday, weather permitting.

 

p.s. - thanks for the positive and helpful contributions to this post frank_ster. Scooby2.5 and I are just trying to get the same amount of voltage most STI's are getting to the pump while retaining the factory progressive pump voltage. As far as we can tell, you can attribute most of the gains in pump voltage to the size of wiring in the STI harness vs. the LGT harness.

There is clearly larger wiring between the FPCM and the pump in the factory harness of the STI. Despite the liberal use of "Carnal Verbs" on my part, this has been a fun and challenging project to work on.

Edited February 25, 2013 by KCwagon

[mwiener2]

so the evaporative emissions don't flood the engine!

 

and i think they fear for life of the pump, thinking that a fuel pump would last at running at its designed speed..

 

Except that doesn't happen (evap) and all fuel pumps are rated for 100% duty cycle, all the time.

[Scooby2.5]

So what you are saying wiener is we do not need to purchase your aftermarket PWM when you start carrying it?

 

Thanks

[mwiener2]

No. You don't need it. But should you want it, that is the best and only option. If modulating the pump was important, there'd be more aftermarket fuel pump controllers.... and there are essentially none on the market right now.

[SCASEYS]

so what did those bugs end up being?

[ClimberDHexMods]

Well a pump running at 100% will produce more heat (along the lines of evaporative emissions). To what extent, I have no idea, but you guys can probably log fuel temperature before / after if you are interested in the practical points of this.

[frank_ster]

^ for heat ? well at 20 amps 12 volts that could possible by a total of 12x20 240 watts.

if you had a big pump.

 

and with the surface area of a non insulated tank, i doubt it would heat up that much.

[KCwagon]

Well a pump running at 100% will produce more heat (along the lines of evaporative emissions). To what extent, I have no idea, but you guys can probably log fuel temperature before / after if you are interested in the practical points of this.

 

Probably depends on the air temperature, amount of fuel in the tank, type of fuel, and size of pump.

Edited February 26, 2013 by KCwagon

[mwiener2]

^ for heat ? well at 20 amps 12 volts that could possible by a total of 12x20 240 watts.

 

And not all of that wattage is converted into heat. The majority of it goes into pumping fuel.

[frank_ster]

at the risk of starting another debate ..

 

the fuel pressurized when at idle and part throttle cruise does no mechanical work and is pushed through a regulator, and returned i would say most of 240 watts is eventually going into heat same as a hydrapack would in a similar situation.

 

and again 240 watts is nothing

[mwiener2]

There is TONS more heat picked up by going through the hot fuel rails than from the pump.

[ClimberDHexMods]

There is TONS more heat picked up by going through the hot fuel rails than from the pump.

 

I've flirted with the idea of putting this on the return line, but probably would not make a tangible difference other than adding complexity to the engine bay, and another point of failure

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[frank_ster]

^ or put a solid aluminum heat exchanger on the frame on the back of the car or on its way back.

[RabidWombat]

Except that doesn't happen (evap) and all fuel pumps are rated for 100% duty cycle, all the time.

 

I'm guessing it has more to due with reliability and gas mileage.

 

While fuel pumps may be rated for 100% duty cycle, cars are not operated that way. Heat is bad for most electronics, so reducing the pump heat is probably going to a have positive effect on the lifespan. Especially, if the vast majority of the time will be spent at the 1/3rd DC.

 

Its could be the difference between having a fuel pump die at 100k miles and 150k miles. In both cases, the fuel pump has lived well into its designed life-span, but the second is better for overall reliability, which is what is tracked by Consumer Reports and other popular reliability sites.

 

Since you're already talking about modding the fuel system to perform well beyond its original design, I'd say it doesn't really matter either way.

 

To put the heat issue in comparison:

240W ~ 1/3 HP, assuming 30% efficent electrical system ~ 1 HP required to run the fuel pump. At idle, you're probably making somewhere between 15-30 HP, so about 5% of the engine power is keeping the fuel pump running at full speed. And probably a 0.5% change in EPA fuel economy. Its small, but if you do 10 small things you get a noticeable bump in mileage.

[mwiener2]

I don't think your math makes sense.

 

If it's a 240w pump, and it's 30% efficient, than 160w would be going towards heating the fuel.

 

At idle, the engine is making a HP or two. Just enough to overcome the frictional losses and to run the accessories.

 

The regulation of the pump is primarily for evaporative emissions purposes.

[KCwagon]

[SeeeeeYa]

FWIW, anyone who doesn't understand the importance of fuel temperature has never been involved in competitive motorsports.

 

It's simple: More heat in fuel, less power. Less heat in fuel, more power. ATBE.

[frank_ster]

well concerned about actual fuel temperature is one thing concerned about how much the fuel pump will heat it up compared to running at a slower speed is another.

 

if you are realy into making fuel cold i could make you a aluminum block that would fit in line with the evaporator and would bring your fuel temps down to the 35-45 deg mark .

[SeeeeeYa]

well concerned about actual fuel temperature is one thing concerned about how much the fuel pump will heat it up compared to running at a slower speed is another.

 

if you are realy into making fuel cold i could make you a aluminum block that would fit in line with the evaporator and would bring your fuel temps down to the 35-45 deg mark .

 

That sounds like a great product that I would seriously debate owning.

 

A lot fancier than a mere cool can and dry ice, and a lot easier to maintain.

[frank_ster]

how many do you want ?

[mwiener2]

I want one in my intercooler

[ClimberDHexMods]

well concerned about actual fuel temperature is one thing concerned about how much the fuel pump will heat it up compared to running at a slower speed is another.

 

if you are realy into making fuel cold i could make you a aluminum block that would fit in line with the evaporator and would bring your fuel temps down to the 35-45 deg mark .

 

Simplest way to make this? Maybe a dual pass solid aluminum heat exchanger, instead put A/C fittings on one of the passes, and wrap the whole thing in some sort of insulation? Or... just run an air-cooled fuel cooler, and be happy.

 

Practically speaking, lots of us with aftermarket fuel systems (and even with stock lines) can just plumb in a temp sensor and see what's actually happening before and after the rails.

Edited March 2, 2013 by ClimberD@HexMods

[mwiener2]

there's a factory fuel temp sensor