Bosch Petrol Pump and Filter Replacement

The original Triumph petrol pump and filter are well documented in their shortcomings. Add to this that even after replacing it with the Bosch replacement kit, which is highly recommended,  the spare tire did not fit in the boot.  Let's solve this challenge and add a few other safety measures to the fuel system. 

    The last and potentially dangerous situation is there is no safety switch to cut power to the fuel pump in the event of an accident. The thought of spraying 100 plus PSI fuel all over in a wreck or rollover just ruins your day. I recommend that all classic cars with electric fuel pumps should fit a safety inertia switch to their fuel system. Follow along, I’ll show you how easy it actually is. All is not lost and the fixes for these challenges are straightforward and fairly easy to implement by the average owner. I won’t go into great detail but will cover the facts and offer my assistance if you decide that you need the help.

     First let’s tackle the electrical issues. The previous owner installed a fuel pump relay in the boot, close to the fuel pump and fed this relay with a heavy 12-gauge wire from the positive terminal on the starter. This takes all of the load off of the wiring harness and ignition switch. This a great strategy for anyone with an electric fuel pump. Second, I ran a separate ground (interior is still out) from the ground lug on the chassis to the fuel pump, also 12-gauge and tied into the ground strap from the battery. The original fuel pump feed wire from the ignition switch now just trips the relay.

  I also added a cutout switch under the dash to manually shut off power to the relay. Anti-theft, not really, but I can turn the ignition on and not run the pump. Seems like a good idea. Next was to add the inertia Switch. These Switches are easily found online and fairly robust so buying used is fine. I chose a switch out of a Ford Mustang or F150 pickup. These devices have a heavy steel ball inside, held in place by a magnet. In a high impact event the ball breaks free from the magnet and collides with spring loaded arm and brakes the circuit. The switch is easily resettable and under normal driving, even with potholes should not trip. The switch is mounted next to the fuel pump relay and is in line with the white control wire from the ignition switch. The shut off switch under the dash is also in line with the control wire. Both must be closed before the ignition will power the pump relay. These could be mounted almost anywhere near the pump. I choose to fabricate a custom bulkhead that sits next to the new aluminum tank and is held in place by the back tank cover and screws that hold the cover in place. 

     I felt strongly that I needed to carry a spare so I worked out a way to relocate the filter and add more angle to the pump mounting bracket. Keeping it nice and low in the corner but also letting it have more space to breath. Relocating the filter also let me move the feeder hoses to better locations and now allows the boot cover board to fit properly over the spare. The feed hose goes out through the LH deck and tucks nicely along the rear shock supports. From there it was an easy run to the pressure relief valve and to the fuel line to the metering unit in the engine bay. A few notes that pertain to this car. All fitting on the pressure side of the pump are AN6. The gravity fill side of the pump is also AN6 or equivalent barb size. The new tank has (for whatever reason) an AN5 fitting. I used an adapter AN5-AN6 and had to drill it out to increase the inner diameter to 5/16th. The new tank while it had AN5 treads already had a larger diameter hole. I will check carefully that this union seals and remains liquid tight. I designed a 3D CAD model of a cover for the relay and inertia switch and finished it with a polycarbonate cove. 

Well the best laid plans sometimes go awry. While I was very happy with the fuel system upgrades above, two persistent challenges kept coming up. The first is the PRV, Pressure relief valve mounted under the car on the frame rail would go into a harmonic hum state. Loud and annoying. Briefly shutting off the power to the pump would stop it but the noise would return in less than a minute. 2nd the boot always had a strong smell of fuel. This was caused by the fuel vapors permeating through the rubber hose from the post filter to the PRV. I could find no fuel leaks anywhere in the system. Both of these seem to be well know issues and yet the fix was not easily done. I have driven the car for almost 300 miles since getting her back on the road. I also knew it was time to rethink the fuel system in the boot and make the needed changes.

The setup on the right show a cartridge filter that I had to temporarily put inline as the sediment filter got clogged and was in rough shape. A new one has been ordered. 

I prioritized the noise as the first thing to fix. Knowing that if I did it right the second would also probably get better. 

The harmonic noise created by upgrading to the Bosch fuel pump and the PRV is well documented and despite having an upgraded PRV meant for the Bosch pump, I still had this persistent problem. The best advice I could find was replace the "Ball and Spring" PRV with a diaphragm type. I purchase one from Prestige Injection in the UK, preset to 103 PSI.  This is the type , picture right, with the challenge that it needs to be installed (or should be) in the boot, next to the fuel tank, not on the frame. Adding to my dilemma was while the new PRV arrived just a week after purchase, there were no directions included. For a seasoned mechanic this would probably be as it should, but it left me thinking about how the device worked, needed to mounted and where the plumbing needed to go. Fortunately for me Carl at Prestige was very patient and I finally knew how it should all go together. In short, I needed to remove the factory PRV from the frame rail including the 90 degree mount and relocate it where I currently had moved the post pump filter. I was not too upset about this as I had previously moved the filter to allow for the spare but had also made it very difficult to change the filter when needed.  So I built a custom bracket for the new PRV and moved everything else out of the way. I bought a flaring tool, tube bender and 5/16 copper-nickel tubing on Amazon.  As a test I bent a few lengths of the tubing and flared a few of the ends. I went to a local speed shop and bought AN6 fittings and a few feet of 150 PSI stainless steel braided fuel line. Making the custom length fuel lines turned out to be not too difficult and after a few learning tries and a youtube tutorial or two, I found it fairly easy. There is a lot going on in the small space beside the fuel tank, so it took a few tries to get all of the parts to fit and play nicely together.. 

Bending the copper-nickel tubing and adding the flares went equally as well.  I fabricated a new mount for the PRV and modified one for the post pump filter. I ended up having to add a union in the hard line, just above the Bosch pump. This helped with assembly and facilitated easier installation of the hard line from the new PRV valve to the original flared fitting of the fuel line going to the MU. The new location of the post pump filter allows for very easy replacement.  I was also able to replace the pre-pump sediment filter and then reassembled the wiring and enclosure for the pump relay and the new inertia safety switch.  With the rubber hose gone, my hope is that the fuel smell will be greatly reduced. 

Costs

• New PRV valve from Prestige        $ 185.00 US ( included shipping)
• AN6 fittings and braided fuel line  $ 149.00 US
• Flaring Tool.                                       $ 30.00 US
• Tubing Bender.                                 $43.00 US
• Copper-Nickel Tubing, 20ft roll.     $45.00 US
• Various Brass flange fittings.          $ 15.00 US

Total $425 

After about 20 miles of driving I am pleased to report that the harmonic hum is gone and in general there is less fuel smell in the boot. On to the next project..... reach out if you have questions.

Rob