| Plumbing the fuel system consists of four parts; suction, high pressure, return, and regulated pressure.
Suction: the section of line that supplies fuel from the tank to the electric fuel pump. High Pressure: This section of line is from the electric fuel pump to the fuel pressure regulator. Line pressure in this section is 30 to 40 psi and the fuel filter is located here. Return: This smaller line returns excess fuel from the regulator back to the fuel tank. This section is usually very low pressure at less than 2 psi. Regulated: This is the regulated pressure out of the fuel pressure regulator that supplies the TBI injectors. Pressure in this section is 12psi. Shown below is the system used on Aaron Cropley's 1971 TR6. There are other methods that I'll mention at the end of this page. |
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Suction |
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The original fuel line from the TR6 tank is 5/16" steel line coming out the bottom of the tank. Because the source is at the bottom, gravity will drain the entire tank if there is a leak. The electric pump used for TBI usually requires a 3/8" supply line, however because gravity supplies the pump, the 5/6" line is sufficient for the TR6. On this car we added a fuel shut off (must be a full flow type). Onto the steel line from the tank a short section of regular 5/16" fuel hose connects to the shut off valve. Out of the valve a 3/8" nipple is used to step up the hose size to match the pump inlet. Regular 3/8" fuel hose connects to the valve. |
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A prefilter has been added because there is no telling how much dirt and sediment are in the bottom of this thirty four year old gas tank. If your tank is clean this could be eliminated as there is a screen located in the pump's inlet. The prefilter is free flowing as it was designed as a diesel filter. The filter number is NAPA 3270. Regular 3/8" fuel hose connects the filter to the pump. |
High Pressure | |
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This is the section that carries the high pressure output from the fuel pump. Steel 3/8" brake line connects to the pump's output and heads forward along the left hand frame member. A 3/8" coupling joins another section of steel tubing and connects to the fuel filter. The filter used is a common GM fuel injection filter, NAPA 3481. The steel tubing requires adapters to mate with the filter, 2 of a NAPA WH 1446 fitting. The 5/16" line crossing over the top of the pump is the return line back to the fuel tank. |
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Steel 3/8" steel tubing continues out of the filter. The steel continues forward until it makes a turn across the back side of the frame crossmember under the engine. The line then turns up and connects with the fuel pressure regulator located on the right inner fender. |
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The regulator marks the end of the high pressure section. On this car a GM TBI regulator was adapted to accept three line connections. Normally this regulator sits atop the throat of a throttle body and in the case of a leak drips fuel into the engine's intake. A concern with this particular regulator is that in the unlikely event of a leak, fuel will drip onto the ground and inner fender. On the plus side it's cheap, perfectly matched for the injectors, and has a fixed output pressure of 12psi. See below for more options. |
Return | |
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The return line returns excess fuel from the regulator back to the gas tank in the trunk. There is little or no pressure in this section so regular fuel hose is perfectly suitable. Starting at the regulator 5/16" fuel hose connects to steel 5/16" tubing. The steel line drops down from the regulator, runs across the backside of the front frame crossmember and is connected to the original TR6 steel fuel line. The connection between the two steel sections is made with a short piece of 5/16" rubber hose at the same location as there was a short hose splice in the original line. |
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Fuel returns in the original TR6 supply line and back near the new pump, is coupled to 5/16" plastic line with a short section of rubber hose. I prefer to use fuel injection style hose clamps whenever possible. The plastic tubing squeezes up through a rubber grommet in the trunk floor alongside the tank vent hose. It continues up to the the top of the gas tank and connects to the vent nipple at the left end. The hose that originally attached to that vent nipple is plugged off. |
| If your tank doesn't have these vent nipples, you will need to make provisions for the return. Either have a repair shop add a 5/16" nipple or contact me for a sender unit with the return built in. The tank connection is something you will need to take care of on your own. Provisions can be made long before starting the conversion. | |
Regulated | |
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Here we are at the end of the line where all the previous plumbing delivers fuel at 12psi. A regular 5/16" hose (minimum size), connects from the regulator to a brass tee at the front carb. A very short section of hose connects the tee to the front carb and a longer section of hose carries fuel to the rear carb. Best to have the regulator within 18" of the injectors. |
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| There are many other ways to run this plumbing, especialy the high pressure section. CustomEFIS recommends a high pressure "push lock" hose. High pressure plastic tubing could be run the entire way or even high pressure rubber hose. Personally I like to use steel lines under the car but newer cars are using plastic or Teflon lines. While the steel 3/8" lines are tough they are also difficult to bend. I've considered offering prebent steel lines as part of the kit. Not easy to ship. What do you think? |
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| Safety is a concern with the fuel pressure regulator so an off the shelf alternative is best. CustomEFIS offers a regulator especially designed for these conversions as part of their kit. Remember the regulator must be the recirculating type to work properly. Aeromotive makes an adjustable regulator that looks promising too but runs about $100. Most of the aftermarket regulators have a small line used to sense intake manifold vacuum. In case of a ruptured diaphram, fuel would escape down that line and flood the engine. Those same regulators when used with TBI should NOT be plumbed to sense manifold vacuum. That line could be piped to the carb's temerature compensator port, run back to the fuel tank, or vented in a non smog application. Fuel filters are also open to change. For Aaron's car the GM filter was chosen as it is available anywhere and suitable for connection with steel line. Ford uses a filter that is designed for quick disconects but works well with hose. If you have questions or comments just email. |
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