Ask Away! with Jeff Smith: External Fuel Pump or In-Tank Fuel Pump for My EFI?

I’m thinking of installing an electric fuel pump in my ’69 Mustang. It has a small block and carburetor on it right now and eventually I’m going to run one of those self-learning fuel injection systems that bolt-on in place of the carburetor. It seems to me that it would be a lot simpler to just mount a fuel pump outside the tank somewhere along the passenger side underneath instead of pulling the gas tank and converting to one of those in-tank fuel pumps that everyone is talking about. Will this work?

P.T.

Jeff Smith: The simple answer is, yes, you can install a remote-mount electric pump and it will work. But there will be issues with this decision. I will assume you are going to convert to electronic fuel injection at the same time that you will install the electric fuel pump. A small, inline electric fuel pump, like the Bosch electric fuel pump, will work but there are several problems associated with any external pump. Let’s say that you install the pump and plumb a large delivery fuel line and also install the proper fuel pressure regulator. We’ll also assume you have created a return system using the original fuel line. This would also require installing a return bung it the stock sending unit. All of this is relatively easy.

What you will discover is this system will work as long as the stock fuel pickup in the tank is covered with fuel. But when the fuel level drops low enough under acceleration to uncover the pickup, the fuel pressure will immediately drop to near zero and the engine will sag badly. This sag in acceleration will slosh the fuel forward and fuel pressure will return – but only until the car begins to accelerate again at which time the process will start all over again. If this sounds acceptable to you then this will work, but I think we can honestly say that this is basically lame. Of course, keeping the fuel tank at half full or above will solve the issue, but now you’ve just cut your cruising range in half. That’s no good either.

But there are other opportunities that might give you what you want while minimizing installation headaches. Edelbrock and FiTech have come up with a universal fuel sump conversion kit. Think of this idea as a fuel surge tank with a high pressure pump inside. These small tanks hold roughly 2 quarts of fuel that is fed by your existing mechanical fuel pump. Inside the tank is a float to maintain the level, and an in-tank, high-pressure electric fuel pump with an internal return.

You mount the tank in the engine compartment near the engine-driven fuel pump and run a fuel hose from the outlet of the mechanical pump to the inlet of the surge tank. Inside the tank is a float system that will regulate fuel into the tank. A filter then cleans the fuel before it enters the high-pressure fuel pump. The pump then feeds a typical 43 psi (or optional 58 psi) fuel to the throttle body style EFI.

The advantage of this system is that it is very easy to install, assuming there is room in the engine compartment. We’ve seen installations placing this surge tank in the open area between the inner fender well and the firewall. Assuming your mechanical pump was capable of feeding sufficient fuel to feed the engine at wide-open throttle (WOT), the only thing this system does is bump the pressure to the higher 43 psi of most of the aftermarket bolt-on self-learning EFI systems.

The FiTech system is called the Fuel Command Center. The system uses a 340 liter-per-hour (lph) high-pressure pump that is capable of easily feeding 750 to 800 horsepower. The tank measures roughly 8 5/8-inch tall and 6 ½ inches deep so it’s compact enough to fit under the hood.

This is the FiTech Fuel Command Center Sump Kit. The aluminum tank contains a float to maintain the fuel level above the high-pressure fuel pump inside the tank.

Edelbrock debuted a similar product several years ago. The current universal EFI sump kit is similar to the FiTech system but uses a plastic sump and offers a couple of different kits depending upon the fuel pressure needed. The first Edelbrock universal sump fuel kit supplies 49 psi while the second offers 58 psi.

You might be wondering how these systems work with no outside return fuel line like there would be on an in-tank pump system. There actually is a “return” but in this case, the bypass is built inside the surge tank. This works because the distance between the surge tank and the EFI throttle body is relatively short so the pressure remains constant.

This is an Edelbrock schematic of the hydraulic side of the system. It’s relatively easy to plumb. Route a fuel line from the mechanical fuel pump outlet to the tank and then a high-pressure rated hose from the surge tank to the EFI throttle body and the system is complete. All that remains is to wire an electrical relay to supply power to the pump and plug it in.

One advantage to this style of surge tank is not only that it is much easier to install than a complete return-style system, but also if you decide later to sell the car without the EFI, it can be easily removed and the carburetor can be quickly re-installed on the engine.

Of course, there are detractions that must be discussed as well. As with anything that is easier, there are some potential liabilities. The most significant is the fact that you are placing a small reservoir of fuel under the hood of your car. This obviously is of a safety concern, although if you locate the surge tank is a safe location toward the rear of the engine compartment, it could be located so as to not leak in the event of an accident. It’s also important to note that NHRA rules prohibit mounting any fuel line, regulator, or fuel tank like this on the firewall of the car. And we shouldn’t need to tell you that you should not mount this tank inside the passenger compartment.

It’s appears from your question that you don’t really want to incur the extra cost and labor involved with building an in-tank pump and return fuel system, but we should note that the major component costs will be similar. The FiTech surge tank is roughly $400, which is roughly similar to the cost of the Aeromotive Phantom system, which will place a 340 lph pump in the tank. The only other major investment will be a separate high pressure feed line to the EFI throttle body and then the AN fittings and filters required to connect all this together. The Aeromotive Phantom 200 lph system will supply enough fuel pressure to feed a 550 hp normally aspirated engine and is only slightly more money than the FiTech surge tank. The Phantom system will require more effort and will also require a dedicated return line which will increase the cost slightly.

Either system will work fine and deliver equal performance. It comes down to how much effort and money you wish to invest in the project. If you plan to keep the car, we’d recommend a dedicated in-tank conversion as opposed to the surge tank idea, but that’s just us. Hope this helps.