Fuel pump control module

**GTTuner** · #1: 08-19-2010, 05:56 AM

How many here have bypassed the fuel pump control module and replaced it with a relay when they did their Walbro install?

**f1anatic** · #2: 08-19-2010, 06:17 AM

I would like to know that as well. Also please include any and/or all links to the said operation of using a relay.

**rao** · #3: 08-19-2010, 06:20 AM

Making that change would be easy, but why would anyone do this?

**GTTuner** · #4: 08-19-2010, 06:33 AM

Quote:

Originally Posted by rao

Making that change would be easy, but why would anyone do this?

Thanks for chiming in rao. I figuired why run the pump at less than 100%?

Why does Subaru do this? I just want smooth consistant fuel delivery from this pump before I tune since my IDC's are up pretty high.

Your thoughts are apprecieated! ( Sorry, I'm going to make you type today

)

**rao** · #5: 08-19-2010, 06:39 AM

They do it to reduce the heating of the fuel and evaporative emissions. In a nutshell, the pump will run in 3 modes: 1/3 at idle or no load, 2/3 at low load and 100% at high load. There is ABSOLUTELY NO REASON AND NO BENEFIT to running the pump 100% at all times.

**SubOperator** · #6: 08-19-2010, 06:51 AM

Paul, have you looked into 08+ WRX & Sti pumps ? I was looking at 245lh ones AVO is selling for 05 LGT with variable voltage support, and they list it as compatible with 08+ Wrx, Sti and FXT. My thought was to get one of those and retrofit it into my LGT. I was wondering what the flow is on those pumps. Don't think I like the idea of fuel pump running at 100% capacity all the time.

**holyjoetart** · #7: 08-19-2010, 06:52 AM

+1. The life of your fuel pump will also be shorter.

**m sprank** · #8: 08-19-2010, 08:58 AM

I have debated for a while installing a relay to make the Walbro get full power all the time.

Only because the Walbro is not designed to run at different voltages. Sure any 12vdc electrical motor will operate at about 5-6 volts. Even many 110v motors will operate at less voltage (just hook them up to a light dimmer and watch). But I am hearing that the failures associated to Walbros (fewer than the rumors portray) are most likely due to feeding them low voltage and causing the motors to overheat and fail.

Rao, any thoughts (honestly, not sarcasm).

**executor485** · #9: 08-19-2010, 10:07 AM

/subscribed... Interested to hear some real ideas and thoughts as I will be installing my walbro soon.

**GTTuner** · #**10:** 08-19-2010, 10:17 AM

Quote:

Originally Posted by m sprank

I have debated for a while installing a relay to make the Walbro get full power all the time.

Only because the Walbro is not designed to run at different voltages. Sure any 12vdc electrical motor will operate at about 5-6 volts. Even many 110v motors will operate at less voltage (just hook them up to a light dimmer and watch). But I am hearing that the failures associated to Walbros (fewer than the rumors portray) are most likely due to feeding them low voltage and causing the motors to overheat and fail.

Rao, any thoughts (honestly, not sarcasm).

m sprank......exactly my thoughts on this. The OE pump is designed to run on lower voltage but can the Walbro stand up to this?

sub op, I'll look into the Sti pump.

**GTTuner** · #**11:** 08-19-2010, 10:18 AM

Another thought on this; Has anyone had one of the FP control units fail?

**Th3Franz** · #**12:** 08-19-2010, 10:21 AM

The ECU can only deliver a limited amount of electrical power. If you put in a big pump or more than one that need a high current draw to reach its rated pressure, the stock ECU might not be able to supply enough juice. For now, on my friend's car with dual Walbros we have relays in place drawing current directly from the battery. I have a background in power electronics so I am designing a circuit that will use the stock fuel pump control to reduce the speed of the pumps for idle and low load situations.

Why would lower voltage cause a motor to overheat and fail?

**John M** · #**13:** 08-19-2010, 10:25 AM

NSFW has found the fuel pump duty cycle tables but right now it's not a standard definition. Apparently it's different in each ROM revision so he's got to manually locate it for each ROM.

Once it's been made available for all ROMs, it's simply a matter of typing in 100% for all values -- no hardware change required. I'd want to do this even if I went to a relay so it'd have a steady trigger input.

**rao** · #**14:** 08-19-2010, 10:31 AM

Quote:

Originally Posted by m sprank

I have debated for a while installing a relay to make the Walbro get full power all the time.

Only because the Walbro is not designed to run at different voltages. Sure any 12vdc electrical motor will operate at about 5-6 volts. Even many 110v motors will operate at less voltage (just hook them up to a light dimmer and watch). But I am hearing that the failures associated to Walbros (fewer than the rumors portray) are most likely due to feeding them low voltage and causing the motors to overheat and fail.

Rao, any thoughts (honestly, not sarcasm).

That is complete BS.

**Th3Franz** · #**15:** 08-19-2010, 10:34 AM

Quote:

Originally Posted by John M

NSFW has found the fuel pump duty cycle tables but right now it's not a standard definition. Apparently it's different in each ROM revision so he's got to manually locate it for each ROM.

Once it's been made available for all ROMs, it's simply a matter of typing in 100% for all values -- no hardware change required. I'd want to do this even if I went to a relay so it'd have a steady trigger input.

I think the switching frequency is high enough where the relay stays closed but I haven't had a chance to measure it directly yet. I'm waiting on a high-speed DAQ card to do it.