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DIY: Upgrade stock FC fuel pump hanger electrical bulkheads and pump mount
There are now several full replacement solutions for the FC fuel pump hanger. However while impressive, at costs of $400+ and often with lead times, they can be excessive for the needs of many owners. I would like to share what I've done to upgrade the electrical bulkhead connections to 30A+ capability, and upgrade the fuel pump mount to something better than a worm clamp around the pump...all for less than half the cost of a billet hanger.
Electrical Bulkheads
A single modern Walbro DCSS fuel pump (models going by street names such as 400/450/525/535/Hellcat/etc.) is easily capable of supporting the 3-450whp level that has become common for the FC. To safely extract the required performance from these pumps, the wiring must be upgraded to support the high current draw vs. a stock pump. Normally this only entails a fuel pump "rewire" which eliminates the stock fuel pump relay/resistor and wiring, but rarely does it include upgrading the bulkhead connections through the hanger.
Take for example a Hellcat 525 pump (with check-valve): a common setup of 43.5psi base pressure, 16psi of boost, plus some restriction from the fuel lines will draw 20A+. The factory M4 bulkheads and potted 18awg connections are just not capable of providing that kind of power without notable voltage drop and heating of the conductors.
Despite the best intentions, when people do attempt to upgrade the bulkheads they often use methods such as compression grommets or non-fuel rated and non-sealed battery bulkhead terminals, which lead to issue down the road. See this thread for some examples of what not to do, and why they are problematic: https://www.rx7club.com/3rd-generati...tions-1128234/
I've personally bought and used 3 different bulkhead solutions, comparing them below.
Solution by EFI Hardware is by far the most well engineered offering I have seen. This is what I chose to use for my own installation depicted below.
Good:
- Excellent design with custom machined flanged stud, delrin insulators, and sealing o-rings
- Excellent installation instructions with characterization of current capacity
- Requires minimal space once installed, which is a must for the S4 hanger
- Includes conductive carbon grease to further reduce possibility of voltage drop
- Designed to work with very thin hanger bulkheads
Bad:
- Expensive @ ~$19 USD ea. plus shipping from Australia
- Specifies a ridiculously low assembly torque, which can catch inexperienced people out when their in-lb torque wrench won't click. DO NOT over-torque...2nm is essentially less than hand tight.
The Radium solution is a nice and complete kit, but technically is not designed for use on a bulkhead as thin as the FC.
Good:
- Good design with custom machined flanged stud, insulated caps, insulating sleeves, and sealing washers
- Better value than EFI Hardware, but overall still expensive at ~$60 for a pack of 6; this would be good to do multi-pump setups or repair several damaged potted bulkhead connections
- Slightly more compact than EFI Hardware
Bad:
- insulating sleeves are one time use. If you mess up or disassemble, a new sleeve needs to be used
- Not designed for thin bulkheads like the stock FC hanger, but this is commonly sold in the Subaru community with fuel pumps kits for use on similar thickness plastic pump assemblies
The Racetronix bulkhead assembly is massive, it will not reasonably fit on an S4 hanger. It also relies on o-rings to seal around the bolt threads...which I don't trust. I imagine this would have problems with fuel wicking or vapor leak. You will need to grind down the inner flange faces considerably to get the o-rings to seal on a hanger as thin as the FC's.
Good:
- Racetronix offer a grounding version with a stainless steel vs. delrin body, allowing for grounding of the hanger (needed for fuel level sender) without use of a jumper wire
- Cheap at $6.60 USD ea, and shipping from Canada was reasonable
Bad:
- Requires massive footprint
- Sealing technique is questionable
- Requires a lot of decking to seal on a thin hanger
The stock hanger (specifically the S4) can be a challenge to upgrade due to lack of available space for new electrical bulkheads. Below is how I chose to locate my bulkheads and it worked out perfectly. The factory bulkhead studs are potted on the exterior, but can be disassembled with a little force. Mine was repaired with a bolt after the brass stud broke off previously.
I installed the B+ bulkhead in place of the original. The ground bulkhead is a little trickier, and must be carefully positioned between the pump bracket, level sender, level sender bulkhead, and the ground stud on the outside of the assembly. This ground stud must be retained so that a jumper wire can be installed to ground the pump hanger; this ground is required for the level sender to function. This is the easiest way to retain functionality of the sender, and allows you to make the connection external to the tank.
Pump Bracket
The factory pump bracket can accommodate the older Walbro "255" style replacement pumps, but DCSS pumps with the fat base will not mount well. The cleanest solution is to retrofit IRP's FD adapter:
Simply cut off the base of the stock bracket and drill a few holes to mount the IRP adapter. This setup is the perfect height, as it will position the pickup sock perfectly at the bottom of the tank without any guesswork.
The only additional parts required were slightly longer bolts and a nut/lock washer to secure the adapter to the FC bracket.
Install tips:
- This is debated amongst shops on this forum, but I prefer using 5/16" submersible hose. The DCSS pumps have a 3/8" outlet, but the FC pickup tube is 5/16". A 3/8" hose just fits too loose for comfort, even with doubled-up clamps. A little premix to lube the outlet and a quick soak of the hose in boiling water lets it slide on like butter. I have personally run this previously for 5 years with no signs of premature hose failure.
- Mount the pump up as "high" as it will go. The outlet should kiss the pickup before the pump base hits the adapter. This positions the pickup sock exactly where it needs to be in the S4 tank. Note, S5 tank is deeper and will require verification on your end.
Completed assembly:
Hopefully this information will help some in the future to have a safe and reliable fuel pump upgrade, without breaking the bank on a new hanger.
Last edited by DC5Daniel; Oct 24, 2021 at 09:22 PM.
Using the stock filter sock when replacing the fuel pump
Hi everyone,
When I replaced my stock fuel pump, I got a new pump with 100 Liters per hour output. The specs call for at least 80 lph so it was a go for my 88 GXL non-turbo engine.
The fuel pump sock with the new pump was a flat sock versus the tall sock on the original pump!
I cleaned the stock sock, it was not too clogged up.
After 150K miles on it I was surprised to find it and the gas tank in good shape!
Please let me know if this was the correct thing to do?
With the pump removed I will clean out the fuel tank with I coat hanger and rags.
After 35 years I expected some rust in the fuel tank, happily it looks fine!
Congratulations on having a clean tank. Mine was completely trashed. I bookmarked this thread so I can rebuild the sending unit later on.
The OEM fuel sock is supposed to be quite a terrible design based on some threads that I have read here. I am sure either one will be fine if you haven't had troubles yet. Perhaps someone else will chime in too.
I’d keep the flat stock for your new pump since it was designed to work with your new pump at the full flow rate. Simulation software and design has come a long way since 1990, so the new filter will be perfectly adequate for your needs despite the appearance of being smaller and having relatively less surface area.
While your old filter may look clean and usable, who knows how much actual filtration it’s doing at this point, or if it might completely disintegrate the next time you’re at 7000 RPM.
I’d keep the flat stock for your new pump since it was designed to work with your new pump at the full flow rate. Simulation software and design has come a long way since 1990, so the new filter will be perfectly adequate for your needs despite the appearance of being smaller and having relatively less surface area.
While your old filter may look clean and usable, who knows how much actual filtration it’s doing at this point, or if it might completely disintegrate the next time you’re at 7000 RPM.
Thanks for the reply, good point about old versus new designs.
I was able to find a new oval Mazda gasket for the unit, part number: FC01-60-962.
Hi again,
I came across the machine screws used to attach the sending unit to the gas tank. I needed to drill out only two when I removed mine!
Part number 9983-30-408 for five screws, should be a package of eight!
I am going to stuff some foam around the unit, found a peanut shell on top of the tank by the sending unit, I do not need my fuel pump wires nibbled on!
