Installing a fuel-injection system on a classic muscle car that was originally equipped with a carbureted fuel system requires careful planning and component selection. Many components that go into a fuel system, including the tank, fuel pump, lines, fittings, and filters, must be replaced or upgraded. Simply installing an electric fuel pump does not work. The fuel-pressure requirements alone necessitate detailed planning, including pressure regulator, filtration, and line sizing.
You have the choice of an in-tank or externally mounted fuel pump. Most owners opt for the in-tank pump because of improved performance and reliability. In-tank pumps are more complicated to install, but tend to last longer, hold higher pressure, and are quieter. You need to detach the tank from the chassis before installing the pump and sending unit in it, or you could buy a complete aftermarket tank. Virtually any aftermarket EFI in-tank pump can supply the 60-psi fuel pressure required. Many builders recommend the Walbro 340 in-tank pump because it holds higher pressures and provides excellent performance for LS engines. Many in-tank pumps are available. The key is to buy a pump that is suited for your application. The stock F-Body fuel pump assembly can be purchased from GM dealers and used for retrofits.
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When opting for an in-tank pump, you need to either buy a tank with a preinstalled EFI pump or install the pump in the existing tank. Both options can be pricey, but there are ways to keep it on the cheap as well. New tanks can cost upwards of $1,000. Companies such as Aeromotive build custom stainless steel gas tanks with built-in in-tank pumps. These tanks are well-built and easy to install. Each Aeromotive Phantom EFI fuel tank features a dropped sump in the top of the tank. This allows for adequate floor clearance. Each EFI tank comes with a new high-volume high-pressure fuel pump to feed the LS engine. The A-Body tank is a drop-in fit.
Ambitious builders can choose to modify the stock tank themselves. Note that the following procedure requires welding on a gas tank. Serious injury or death can occur if the utmost care and preparations are not followed.
You can alter your stock tank to take an EFI fuel pump in three ways. The bargain-basement method is to take the stock sending unit assembly out of the tank, cut off a short section of feed line (about 11⁄2 inches, depending on the depth of the tank and the length of the pump), and fit the pump to the stub using fuel line and hose clamps. The important thing here is to make sure the pump is mounted about 1/4 inch off the floor of the tank with a filter sock resting on the bottom of the tank. This keeps impurities out of the pump while getting the most fuel out of the tank.
The pump must be supported; a piece of steel rod can be welded to the underside of the assembly plate. The pump is then clamped to the rod so it remains stationary. This method doesn’t work for all tanks, especially shallow tanks, and you may be hampered by the diameter of the stock assembly. Also, the fuel-level sending unit may be in the way, depending on the application. This method keeps the stock feed lines in place and eliminates floorpan clearance issues. One drawback is the lack of a fuel sump, which traps fuel around the pump inlet, ensuring it does not run dry. Running an in-tank pump dry is very destructive; they don’t last long when run dry.
The second option involves welding on the tank. This is extremely dangerous and should not be attempted in haste or by novices. All old fuel must be removed, and the tank thoroughly rinsed, drained, and rinsed again until there is absolutely no possibility of any remaining fuel vapor. If you smell a hint of gas, do it again. To add an extra measure of safety, fill the tank with water or inert gas such as argon while the welding is being performed. If you have any doubt, seek the help of a professional. Most fuel tank builders offer their services for retrofitting tanks. Employ their services if you can.
Installing a custom in-tank pump in the top of the tank often requires a recessed panel on the top. The fittings clear the floorpan and give you a flat surface to mount the new assembly. If you place the top sump to the side of the original, the stock sending unit can be used, simplifying the process. This requires a boxed section be built and welded to the top of the tank. Then a fuel-pump assembly unit is built with both wiring and inlet and outlet fittings. This piece should have a bar or rod on the inside portion of the tank for the pump to mount to.
Using 90-degree hose barb fittings is usually the easiest way to get the fuel in and out of the assembly. These fittings must be sealed tight so they do not leak. The entire assembly bolts to the sump.
In addition, by installing baffles to the inside of the tank, fuel surrounds the pump at all times. These should be added before the top sump is installed.
You can also weld in a sump in the bottom of the tank. This sump is placed directly below the pump, but the pump is installed in the lowered section, with the filter sock on the floor of the sump. Tanksinc. com offers an upper tank mount, complete with a fuel pump and baffle. This reduces some of the legwork in building this piece and ensures the pump always is covered with fuel.
The third option allows you to install a truly high-performance fuel pump into a stock fuel tank without welding. Aeromotive offers two retrofit in-tank pump kits: the Phantom and the A1000 Stealth. For basic street performance use, the Phantom 340 is suitable. This kit allows you to simply cut a hole in the top of the tank, drop in the pump, bolt it down, and hook up the lines. The kit comes with the seals, hardware, and a drill jig to ensure the holes are in the right place. The 340 supports up to 700-hp supercharged EFI engines, or 1,000-hp supercharged carbureted systems. That leaves plenty of room to power a stock 400 LS3. The Phantom system fits in just about any tank, so this is a good option that takes out the guesswork.
For more serious performance engines, the Stealth A1000 system feeds up to 1,300-hp EFI systems and 1,500 for carbureted engines. Installing these systems takes slightly more effort than the Phantom kit, but not much.
Inline Fuel Pumps
External or inline pumps offer a simpler installation and are usually more affordable, so you can make roadside swaps. The main gripe over inline pumps is the noise. The relatively quiet and smooth-running Gen III/IV engines do not drown out many external sounds, including these inline pumps. Therefore, drivers may hear the whir of the electric pump sound over the engine with a stock-style quiet exhaust. For most builders, the added noise isn’t a problem but rather an inconvenience, but for a show car, a noisy pump might be considered a serious drawback.
The real drawback for an inline pump is that the fuel line is only pressurized after the pump, so the tank to the pump is gravity fed. Anyone who has dealt with a modern high-performance external fuel pump can tell you that life is difficult when you lose the siphon in the tank. Simply having the pump in the tank maintains a constant supply of fuel to prevent those hard-cornering and acceleration woes that come with a stock tank and an inline electric fuel pump. Inline fuel pumps also require a more substantial return line system because of the long distance between the regulator and the fuel tank. Inline pumps are also subject to failure through heat. The only thing that cools the pump is the gas flowing through it.
Not all inline pumps are created equal. External pumps come in all different shapes and sizes, with most of the market consisting of low-pressure units designed for carburetors. These pumps deliver 6 to 14 psi, and are not close to the 60 psi required to operate an LS engine. Any less than 60 psi and it leans out and does not run well, if at all. You have plenty of inline EFI pump choices. Many builders prefer the Walbro GSL 392 external pump. These pumps are well-suited for Gen III/IV engines and can supply the pressure needed.
Installing an inline pump is simple, but there are a few caveats. The first is to always install a pre-filter before the pump, so the pump does not become clogged and ruined. A pre-filter is basically a screen-style filter that traps the big stuff. A micron filter should be placed after the pump to catch small contaminants. Do not install a micron filter in front of the pump (between the tank and the pump) because it impedes the gravity feed and there is not enough force to push the fuel through a micron filter.
Make sure the pre-filter is large enough to free-flow the fuel. A small pre-filter restricts flow to the pump, causing cavitation, and burns up the pump. A stock-type metal canister pre-filter works great, but they are not pretty. Most aftermarket fuel pump makers have large-capacity pre-filters if you want one that looks good. Most of the aftermarket pre-filters are rebuildable as well.
Cavitation is a natural process that occurs when vapor bubbles are induced in liquid under pressure. All electric fuel pumps are susceptible to this force. Its most common cause is installer error when an inadequate fuel supply increases the suction on the inlet side. Cavitation is literally boiling the fuel through pressure. Vapor bubbles form and then split, imploding, causing a micro explosion. This is extremely damaging; even a few minutes of cavitation can ruin a fuel pump.
Another cause of cavitation is overheated fuel. Not running a return line (deadhead style) or attempting to plumb the return line into the feed line (not into the tank) causes hot fuel to cycle back through the pump, heating it up more. The hotter the fuel, the easier it is to cavitate or even vapor lock. Yes, EFI systems can vapor lock too. This is the reason a proper return system is so important for EFI.
The most important aspect of any electric fuel pump is the wiring. It is most difficult to get solid grounds because paint, rust, and scale inhibit the ground. Always be sure to remove the paint and anything else from the ground location, so you have clean metal. Electricity requires equal grounding and positive current flow. A bad ground is just as bad as a faulty positive feed. Electric fuel pumps require a lot of current; running a relay circuit from the pump trigger lead, along with 12-gauge positive and negative wires to the fuel pump, provides ample capacity. This ensures the pump receives the required amperage without overheating the wires. Do not run a 16-to-24-gauge primary wire to a fuel pump because it will cause a fire. All fuel pumps require at least 12-gauge power wire, with the larger pumps needing 10-gauge wire. This includes both power and ground wires.
Gen V LT-series engines are different from the LS series, particularly in the fuel system department. All LT-series engines are direct-injection, meaning the fuel is pressurized to more than 2,000 psi and injected directly into the combustion chamber, much like a diesel engine. Because of this, the fuel system is dramatically different. Instead of a basic fuel pump and regulator, the factory pump is controlled by the ECM and a fuel pump module to control the pressure.
A special pressure sensor in the fuel line monitors the pressure of the fuel, which is maintained at 72 psi. Rather than use a regulator, the pressure is managed through PWM control of the pump. Essentially, the ECM uses PWM to control the speed of the pump, ensuring constant full pressure with no delays. This complicates the fuel system for the LT-series engine swap. You can’t use just any pump; the pump has to be able to be PWM controlled. Before you purchase a pump, make sure it is PWM capable.
The LT system is returnless to keep the fuel temperature down; therefore, hot fuel does not return to the tank and the fuel temperature stays down. The pump requirements are 72 psi at 45 gallons per hour (gph) with the Chevrolet Performance control system. Although this system is more complicated in terms of wiring, it does eliminate the need for a return line.
Many swappers already have an existing electronic fuel system in their vehicle. Swapping an LT into that scenario could mean buying new parts, but all is not lost. You can bypass the PWM-style pump system by using a standard electric pump with a return line and regulator set to 72 psi at 45 gph. That is fairly high for a street pump, so make sure your pump is capable of providing the required flow and pressure.
Installing the PWM controller is relatively simple, but installing the fuel pressure sensor is a bit difficult. First, you need an inline adapter with a pressure sensor port positioned at 90 degrees, or 5 to 85 degrees to the flow of fuel, according to the GM manual for the fuel controller. Because plenty of these fuel sensor adapters are available, this is relatively easy.
The problem is that most of the adapters are for 1/8-inch NPT fittings, and not the 10-mm threads required for the GM sensor. Finding a 1/8-inch NPT male to 10-mm male adapter is the difficult part. What you can find easily is a -6 AN male to 10-mm adapter. To use this, you need an aluminum fuel log or Y-block fuel splitter and a -6 AN to 10-mm male-male adapter. This allows you to connect the sensor into the fuel system. (I made one with a leftover piece of fuel rail from another project.)
The PWM pump controller is a plug-and-play component, but the pump wiring is not. Three wires come off the pump module: yellow with a black stripe, gray, and a smaller-gauge black wire. The yellow/black wire is the ground, the gray wire is the power side, and the small black wire is the shield. If you have a GM pump with a shield pin, connect the small black wire to that pin; if you have a pump without a shield pin, leave the wire unterminated and tape it to the other wires.
Because of the nature of PWM control, you may experience electromagnetic interference from other electronics in the car. To keep this from interrupting the control signal, the two main power control wires are twisted with a third shielding wire. This wire is grounded to the chassis near the pump. The Chevrolet Performance wiring harness comes with a certain length only; the A-Body chassis absolutely requires longer wires. To maintain the shielding, you must twist the wires a minimum of 27 twists per 8 feet of wire.
The best way to ensure that the wires are correctly twisted and don’t unravel is to braid the three wires together. It does not need to be a tight braid, rather a consistent loose braid, wrapping the wires around every 3 inches or so. Do not use crimp connectors for these wires; make sure you solder them well and use shrink tubing.
Most EFI engines (except for 2014–up Gen V LT-series engines) require return lines. This can sometimes be confusing because Gen III/ IV engines use a single-line fuel rail. The 1997–1998 Corvettes and 1998– 2002 F-Body LS1s used a dual-line fuel rail. In 1999, the Corvette LS1 went to a single-line rail, using a
filter regulator near the fuel tank and running a short return line back to the tank. This configuration is much simpler and requires only a single line run the length of the vehicle. Many builders prefer to run two lines the distance of the vehicle with the dual-line fuel rails.
The benefit of running a full-length return system is cooler fuel. The fuel does not sit in the lines, heating up from the pressure. Instead, a constant flow of fuel is running through the lines, ensuring cooler fuel and, therefore, more power. This, of course, requires two sets of fuel lines: a 3/8-inch line for the feed and a 5/16-inch line for the return. Some muscle cars and trucks came with return-style mechanical pump fuel systems, but these are not the norm for older vehicles; most were deadhead systems, meaning that the fuel simply stops at the pump until it is sent on to the engine.
If you choose the simple one-line route, you need the 1999-up Corvette filter regulator. This unit has two lines (an input and an output): one on the side for the fuel tank, and one on the other side for the output, which goes to the engine. It is a one-line system to the engine, and there is a short return line from the regulator/filter to the tank. This pre-set regulator provides the correct 60 psi to the engine, which pressurizes the entire fuel line while pumping the excess fuel back to the tank. This is typically mounted as close to the tank as possible to minimize the length of feed and return lines to the tank.
For a dual-line system with the pump in the tank, you need a filter between the pump and the fuel rails. It is best to filter the fuel as soon as possible to keep the fuel lines as clean as possible.
Installing new lines is not difficult, but it can be nerve racking. You have three ways to accomplish this task: install pre-bent hard lines, bend new hard lines, or run braided hose,. Using pre-bent hard lines is the simplest method if the vehicle has the fuel tank in the stock location. Pre-bent lines such as those from Classic Tube and Tube Tech are patterned after the original lines in the car and should fit just like the originals. That is not to say that compromises and tweaks are not needed along the way.
Bending and installing custom lines most effectively transports fuel the length of the vehicle, but it is much easier said than done. This is a challenging task that requires some metalworking skills, and therefore the task is frustrating at best for the novice. Tube manufacturers such as Classic Tube offer custom bending services. Using coat hangers or other wire, a pattern is bent by hand and sent to the maker. The maker bends a set of hard lines to your specifications and ships it to you. This ensures quality bends with proper flare where you want them (without kinks) and without the aggravation of doing it yourself.
The third option is to use flexible hose for the long runs. This works, but you should use braided hose rather than plain rubber hose to protect from road debris damage. The chance of road debris snagging a long braided fuel line is much higher than with a hard line. Rubber lines are not the best option, either. Rubber lines dry out and crack much faster than hard lines corrode, so you must replace the rubber lines eventually.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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