iWire FPC Hardwire Kit, FPC, fuel pump controller

Upgraded Fuel Pump Controller Explained

May 3, '21

In this blog post, we clear up common myths and misconceptions about the upgraded fuel pump controller.

When we came up with the idea of an upgraded fuel pump controller (yes, it's the one from a GTR) and began testing it, we had preconceived notions about why the stock fuel pump controller was failing. After exhaustive testing and feedback, we were surprised at the results but learned more than we could have imagined. However, during the last year or so, people started making their own judgments without this background information about what the upgraded controller does and why it's used, which created several myths and misconceptions that we aim to clear up here.


Cliff Notes

The stock fuel pump controller will be just fine if you address the potential failure points and have the proper wiring solution, like our hardwire kit with stud bypass.

  1. Fuel pump controller failure is NOT due to heat.

  2. Fuel pump controller failure is NOT directly due to higher flow pumps.

  3. Fuel pump controller failure IS due to an external situation where power and ground touch and fry the controller.

  4. A common situation is when the stock connector terminals on the fuel hanger overheat due to the increased current running through the terminals than they were designed for. Eventually, the connector melts, leading to power and ground touching, but our hardwire kit with bypass stud kit eliminates this issue.

  5. Another typical scenario is the pump gets too hot and internally shorts. 525LPH pumps do this more often than smaller pumps which is why we don't recommend them.

  6. The upgraded fuel pump controller does NOT increase the voltage on its own

  7. The upgraded fuel pump controller does NOT replace our hardwire kit

If you want the whole story, please read further!


Backstory on the iWire Upgraded Fuel Pump Controller:

When we started selling the iWire Fuel Pump Controller Hardwire Kit, we noticed an increase in fuel pump controller failure, especially in cars utilizing large fuel pumps like the Walbro 525 LPH. Initially, we thought the FPC failed because it was overheating, which is why we went with the bigger controller that should be able to dissipate heat better. This was the initial trigger for trying this upgraded OEM controller from another manufacturer. Needless to say, we were pretty excited when we found out the upgraded controller was plugged in and performed well. As we continued testing the upgraded controller and confirmed that there were no gains in efficiency or fuel flow, we wanted to continue to figure out why FPCs were failing.


When comparing the stock fuel controller to the upgraded controller, we struggled to recreate any failure. We put the stock FPC to the test and abused it well beyond anything the controller would see in the real world and could not get the stock FPC to fail in-house. During testing, we recorded temperatures over 250 degrees with the current flow at over 25 amps (far beyond any pump's peak draw or at least the time spent at that current draw) for hours on end, and it did not fail. There were even visible air bubbles in the circuit board gel from the heat, but the controller continued to function normally.


So if the stock FPC can handle all that heat, why does it fail with large pumps?

Let's first look at why the Fuel Pump Controller is in the car in the first place. One big reason is safety because it allows the ECU to turn on and off the pump, so it only runs if the engine is running. The other reason is for fuel economy as well as keeping lower fuel temps by running with low (33%), medium (66%), and high (100%) settings. To run these settings, the FPC must act as a resistor. Resistors slow down current flow (to run the pump a 33% and 66%), but the byproduct of resistance is heat. Most of the work of that big metal casing with fins is to act as a heat sink to dissipate all that heat, but the electronics inside are relatively simple and are quite good at surviving at high temperatures and shedding heat. With that being said, be wary of any fuel pump controllers designed without metal casings because they are much more likely to fail since they cannot dissipate heat.


What does this mean for your fuel pump upgrade?

The only way we could get a stock fuel pump controller to fail was some external event that caused a short in the wiring. In simple terms, power touches the ground and damages the internal circuity of the controller. This can happen for two reasons:


1. The stock fuel tank connector fails and grounds out, therefore, shorting the FPC

This stock connector fails because it is not designed for the amperage the larger pumps draw. With this increased draw, the terminals get hot, which causes the plastic connector to get hot and melt. When this happens, the terminals touch and short power to ground. We fixed this issue with our Stud Bypass Kit, which is a standard option in our hardwire kit.


2a. 450 LPH and smaller - The fuel pump in the hanger internally shorts which fries the controller. This tends to happen when the pump gets too hot because there is insufficient fuel in the fuel tank to keep the pump cool. The first step to prevent this is ensuring you always have plenty of fuel in the tank! We also see a combination of the above high current issue through the stock terminals and low fuel that causes the damage.


2b. 525 LPH Pumps - This is where the 525 issues come into play. We believe the 525 pumps are pushed up to the case's (housing) limit for the amount of flow of a pump with this physical dimension. As a byproduct of this, we think that the 525 pumps internally short due to overheating, which happens much easier than the lower flow pumps of this size. Therefore, the iWire recommendation is to avoid running 525 LPH pumps.

2c. We've also found that the marginal increase in flow from the 525 LPH over the 450LPH pump comes at too high of an electrical current cost to make them worthwhile.


Another note (OK, fine "notes" plural) on 525 LPH pumps - We also have found from a practical sense the 525 LPH pump is an in-between size (as weird as that sounds).

  • The first reason is that a 525LPH pump is too large for the application. It's not necessary to install the largest pump that you can. It's more important to pick the correct size pump for your application with some headroom.

  • The second reason is if the car is making enough power to require nearly 525 LPH of fuel, then the appropriate pump setup would need a bit more headroom, leading to the better solution being 2x340LPH pumps or 2x450 LPH pumps. Both setups are OK with the stock FPC, and the Radium Hanger is the best way to do this, and we make them plug and play.


Myth 1: The Upgraded Fuel Pump Controller Adds More Fuel - FALSE.

A bigger fuel pump controller does not increase the pressure or fuel flow. We only utilized the bigger controller because it is a bigger heat sink for the large pumps. The increased fuel pump size and the increased voltage to the pump is provided by the iWire FPC Hardwire Kit and increase the amount of fuel the pump provides, not the controller itself. We have found that the OEM FPC can handle the increased current draw and heat without issue.


Myth 2: The Stock Fuel Pump Controller will Fail with an Aftermarket Fuel Pump - FALSE.

As we mentioned before, the only way we've been able to get an FPC to fail is when the system shorts and power touches ground. We’ve reduced this possibility with our Stud Bypass Kit, and we recommend keeping lots of fuel in the tank. Our upgraded FPC does not change any tuning settings, safety settings, or other variables, so it is not needed for pumps smaller than 500 LPH.


Myth 3: Plugging in the Upgraded Fuel Pump Controller into my Stock Harness is All I Need - FALSE.

You could plug the upgraded controller into your stock harness, but without the other upgrades, it will not change anything. If you were to run a 525 LPH pump with your stock harness and an upgraded fuel pump controller, you are almost guaranteed pump failure since none of the other elements of the fuel pump wiring system have not been updated.



Tags: Fuel System