| The benefits of a GM style in-tank electric system over a traditional aftermarket external fuel pump are quiet operation, lower cost, and increased safety. Shown here is my installation.
Keep in mind, my car is a street car that I race, NOT a race car I drive on the street. I never intend on putting a roll bar in this car, so that limits my minimum ET to 11.50 for the local IHRA tracks I race at. Therefore, I designed the fuel system to adequately feed an engine that would do high 11's to low 12's in the quarter mile. I did not want a fuel tank sump, and I did not want a fuel pump hanging under the car or between the gas tank and bumper. I consider this a crash hazard on a car driven on the street. I would also much rather have steel fuel line over expensive braided line that has rubber that can deteriorate.
Some notes:
- The fuel pump I chose is very popular among the Grand National crowd. It is a Walbro GSS307m pump, but sold by Summit Racing Equipment as a Granatelli Motorsports F-body fuel pump, Summit part #GRN-GM722-2, $ 125.95. It comes with a fuel filter sock and pump connector.
- I used a MALLORY 3-Port competition return style regulator, Summit part number MAA-4309 ($ 74.95). This is necessary with the EFI fuel pump to allow the unused fuel to return to the gas tank. The EFI in tank pumps are always pumping at their maximum output.
- I removed the stock 1/4" return line on the frame and ran new steel 3/8" line for the return. At first I tried swapping and using the stock 5/16" vapor line for the return (and using the 1/4" line as the vapor) - but THE 5/16 LINE IS NOT LARGE ENOUGH. The fuel pressure would not come down below 10psi because the regulator could not return the fuel to the tank fast enough.
- Replace ALL of the pressurized 3/8 rubber line on the car with fuel injection rubber hose.
Racetronix sells a nice looking fuel pump kit, complete with a relay and wiring harness. This would actually have been cheaper and easier than what I did, but I wouldn't have learned as much! See http://www.racetronix.com/Racetronix-Buick_Single_Fuel_Pump_Kit.html
|
| | I first purchased a used gas tank from an '86 Grand National.
I purchased a GM original tank in poor shape, not a parts store replacement tank. According to gnttype.org, replacement GN tanks do not have the correct plastic bucket shaped baffle in them, and a turbo Buick will suffer from fuel pump starvation much sooner than if it had a GM tank in it.
The Grand National and replacement Cutlass tank are functionally almost identical on the outside. The GN tank has a different fuel filler neck. I cut the old GN tank open, removed the bucket baffle, and installed it into my shiny Cutlass tank.
BE CAREFUL if you are working on a tank with fuel or fuel residue in it! If you can smell any gas, there are enough fumes to burn! I first used an external electric fuel pump to drain the Cutlass tank, then filled it up all the way to the top several times with water before working on it. After this, it STILL smelled of gas. Be careful!
|
 Click on the picture for a larger view. | | | To the left is the modified Grand National pickup assembly.
I started with the stock Grand National pickup assembly. It comes plumbed with:
- 3/8" feed (pressure) line.
- 1/4" return line. The pump is mounted to this.
- 5/16" vapor line.
Note, the stock GN 3/8 pressure line necks down to 5/16" where it connects to the fuel pump. I cut the 5/16" portion off, and ran a longer 3/8" hose from the pump to the 3/8" line.
If I were to make another hangar, I could net the same result with less work by starting out with the Cutlass hangar. What you need to end up with is:
- 3/8" pressure line.
- 3/8" return line
- a vapor line that is vented to the top of the tank and baffled against fuel sloshing into it.
My GN assembly must have come from a car with a digital dash, because the fuel level sender did not read correctly with my fuel gage. I cut the fuel level sender off of the Cutlass hangar and welded it onto the GN hangar. The fuel sender should read from 0 to 90 ohms. I then had to modify (rebend) the wire that the float attaches to. It is physically bent different so that the larger pickup assembly (because of the pump attached) can actually FIT into the round hole on the top of the tank.
I "hot wired" the pump by replacing all of the fuel pump wiring with 12 gage wire. The stock hangar relies on the ground current to travel through the return line, through the body of the hangar, and then through a wire tack welded to the top of the hangar. The stock return lines are crimped and brazed to the hangar, but this brazed connection often breaks loose, causing arcing (!) My return line brazing had failed, and you could wiggle the return line around. I welded it to the hangar top. I ran the 12 gage negative wire directly to a #10 stainless screw and lock washer. This improves the ground connection. Many of these tips were taken from gnttype.org from their Technical Information Recource archives.
The positive wire runs to a Bosch 25 amp relay mounted on the firewall. The power comes directly from the battery, but runs through a weather packed fuse connector mounted inches from the battery. The fuse holder uses the same style GM fuses the rest of the vehicle uses.
Power to energize the relay comes from a keyed positive source, then through an oil pressure switch. This way, the pump only gets power when the key is on, AND the engine is running. I have a wire going to the electric choke from the oil pressure switch too.
The oil pressure switch has 3 terminals - a center terminal, and 2 outer terminals. The center terminal is normally closed (opens with pressure) to the engine ground. This is what your oil light should be connected to. The other 2 terminals are connected to each other (not ground), but are normally open. With oil pressure, they connect. 1 terminal should be connected to a keyed positive source. The other terminal should be connected to the switching side of the relay.
The oil pressure switch I used was purchased from Napa, Echlin part number ECHOP6634, about 10 bucks. It has a 1/4"NPT, so I had to get a female 1/4"NPT to female 1/8"NPT adapter from the hardware store. I got the pig tail (connector) from a bone yard off of a front wheel drive 3.8 V6. Bring the sender and match it up. It is on the front right side of the motor (front of engine, not car) near the oil filter.
|
 The modified Grand National fuel hangar assembly.
Click for a larger view.
| | | To the left is the completed tank. Click on it for a larger view.
Once the bucket was installed, I welded the seam shut and sealed it with epoxy glue.
Notice the rubber straps that wrap around the tank - they are stock on the GN tank. They have Velcro at the ends to attach the ends. The material is very flexible, and about 1/8" thick.
Notice the wiring harness that comes off the top - It has 3 wires:
- Black ground
- fuel pump power
- Pink fuel level sender signal
I cut the GN connector off of the assembly and purchased a similar pair (male and female) connectors from NAPA. They sell GM connectors with new uncrimped terminals. This way you can run new wire, and crimp on new connectors, eliminating splices. This is how I was able to run larger 12 gage wire to the pump. I cut the end off of the GN harness because I could not buy the matching GN fuel pump connector.
I also purchased fuel injection hose for the pressurized rubber hose. It is different and more expensive than regular rubber hose because it is designed to handle fuel pressure. With a mechanical fuel pump, the fuel line is only under suction. |
 Click on the thumbnail to see the completed fuel tank. | |
