Learning about Fuel Modules
On all modern cars, it is common to be able to drive the car normally until the tank is completely empty. How many times have you put in enough fuel in your modern car to know that there was nearly zero left in the tank? It may have made you very nervous, but the car made it to the gas station.
It is unacceptable to the OEM’s – and to the owners – to keep at least a ½-tank of fuel in the tank in order to have good fuel delivery under all driving conditions.
Imagine driving your car and coming up to your favorite freeway cloverleaf, sweeping turn, etc. But wait, you have to tip-toe through that fun driving because the liquid level in the tank is below 1/2. Does that seem even a bit reasonable?
To solve this problem, the OEM’s have integrated many of the technologies mentioned in the earlier sections, then added a few more to make them better. To make it easier to understand, we will call the device that integrates these features a fuel module.
In short, and what will be laid out further in this section, is that the OEM derived fuel module is simply in a different orbit than almost anything offered in the aftermarket. The engineering, safety, and thoughtful design of these modules makes them a game-changer for aftermarket fuel delivery, and we are fortunate to be able to take advantage of the large-scale manufacturing costs associated with them. There is only one aftermarket company offers an integrated fuel module like those used by every OEM automotive manufacturing company on the planet, and that is KPM (Part Number 67706 and 67707). Even the new Honda Gold Wing motorcycles use a fuel module design! If there were a better, less costly method for reliably pumping fuel, the brain-power at the OEM’s would have it figured out.
Please note that all modern fuel modules will not work in low-pressure carburetor applications. High pressure fuel is needed to drive the jet/suction/venturi pumps. If used in a low pressure / carburetor application they will fail miserably.
Modern fuel modules perform many of the functions that were traditionally handled with separate components.
Fuel filtering, pumping, and pressure regulation can be done in the fuel module.
The fuel module also has a built-in surge tank/reservoir, venturi/jet/suction/transfer pumps to keep the reservoir full, electrical bulkheads, fuel level sensor attachment options, and excellent sealing devices.
Most fuel modules are also preloaded to the reservoir against the tank bottom using springs. This keeps the suction pumps on the floor of the tank and provides structural support. The fuel pump module, with its compressible hat/bulkhead, must be preloaded against the bottom of the tank.
A typical modern fuel module is shown in Photo 1.
The fuel module shown has the following features:
1. An all-in-one fuel filtering. No other filtering is needed or recommended before the fuel rail if the proper lines and line cleaning procedures are used. The exceptions are the Ford GT500 and others that are typically dual electric pump designs.
2. A single line output that supplies regulated pressurized fuel. No return lines or external mechanical engine pressure regulators.
3. A wiring plug/bulkhead connector that passes power and fuel level signals through to a sealed external plug.
4. The large white cylindrical-shaped part is the reservoir. When the pump is running this reservoir is normally overflowing with fuel, hence keeping the pump constantly submerged.
5. 1-3 jet pumps are used to fill the reservoir and keep the pump supplied with fresh, cool fuel.
6. One of the venturi pump connections, the grey nipple on the bottom-left of the reservoir, can be used to connect remote pickups.
7. It’s an OEM validated design.
VaporWorx has performed extensive testing on many modules.
Single modules like the KPM can support up to 1000fwhp @ 60psi on e85. For the 800fwhp and below builds, the Gen5 Camaro ZL1 and Aeromotive Super ZL1 (Part Number 68101) are very capable and low overall cost.
They are quieter than a standard 255lph pump mounted traditionally in the tank, or in-line.
Best of all, even under very low fuel loads the fuel module is still working due to the reservoir.
It has been shown that the module will reliably deliver fuel at very low liquid levels even when used on autocross or road courses. When the corner pickup systems are used on-track, testing has shown that liquid levels can fall to under one gallon and the module will still be effective. During validation testing on-track at Streets of Willow Springs raceway the 1968 Camaro test car (with a wide flat-bottom tank + Gen5 Camaro fuel module) literally sucked enough fuel off the bottom of the tank that it took six (6!) Brawney paper towels to clean up the leftover fuel.
Even without the corner pickups, module performance will not suffer on autocross courses with just one gallon in the tank.
Note the jet pump locations and other features on the module bottom surface in Photo 2
What are those jet pumps, and how do they work?
Jet pumps, aka suction and venturi pumps, use a nozzle-suction effect to move fuel. Shoot a high-pressure stream of fuel through a nozzle and it will create suction. That is how remote pickups typically operate. The other way is by using the fast moving stream of fuel to shove the surrounding tank fuel into the reservoir. Remember as a kit jumping in a swimming pool with a garden hose?
Twist the nozzle to get the smallest stream of water so it shoots way up into the air. Now put the nozzle just under the top of the water. The surrounding water wants to grab on to the nozzle water. Pointing nozzle toward the pool deck can lift much larger amounts of water out of the pool than just the nozzle stream. Given long enough, you could empty the pool. What is happening is the high-speed/low mass of the nozzle stream is turned into a low-speed/high mass. The same think happens with the modern fuel module, fuel is lifted from the bottom of the tank and dumped into the top of the reservoir. If only you could have convinced your parents that the hose in the pool was a science experiment……
An often overlooked benefit of the lower reservoir is the amount of inlet head pressure that elevated fuel level provides.
When liquid levels in the tank are low, the inlet head (height of the fuel above the inlet) is also low. The pump, not being very good at suction, will have poorer performance vs. the same pump with more inlet head. The higher the inlet head pressure to the pump, the lower the chances of cavitation at the inlet.
The lower the inlet head, the greater chance of cavitation at the pump inlet, and hence the resulting loss of fuel pressure.
This cavitation is also known as vapor lock. Unlike carburetors, vapor lock on EFI systems typically happens at the inlet to the electric pump due to high fuel temperatures and low inlet head pressure. How many modern cars have vapor lock problems? If reasonable methods are used to keep the fuel lines away from heat then fuel boiling in the lines will not occur. Vapor lock on high-pressure EFI fuel systems typically happens at the inlet to the pump.
In order to make the fuel module shown above work in a standard mechanically regulated 4bar/58psi EFI system, the fuel pressure regulator in the module must be replaced. A VaporWorx fuel pressure regulator can be used to convert the Gen5/6 SS fuel modules to 4bar constant fuel pressure operation.
This arrangement will provide a fuel pressure vs. output curve very similar to that of a C5 FFR.
Note: Higher output fuel pumps like the Gen5 ZL1, Gen6/6 ZL1, C7, Ford GT/GT500, and other high-horsepower applications typically should have a different control strategy. However, if the car is driven a lot even the Gen5 SS fuel pump module will benefit from PWM control systems, just like the OEM’s do.
In order to mount the fuel module into the tank, a VaporWorx fuel module mounting ring is required.
This ring, made of 304 stainless steel (Product Number 68701) or 6061 aluminum (Product Number 68702), will weld on to the top of the tank.
Note that the fuel module, with its downrods and preload springs, must seat flat and be preloaded against the bottom of the tank. The fuel module is not designed to “hang in space” where the weight and side loads of the lower section are transferred through the downrods and into the bulkhead hat. If this is done the downrods will break out of the hat, leaving the entire lower section unsupported and flopping around in the tank. The fuel module must be preloaded against the bottom of the tank.
It is acceptable to have the sealing surface of the mounting rings/fuel module to be under the liquid level provided that the hat is fully sealed / plug vents, etc.) It is this way in the OEM application as well.
Above the mounting surface of the ring a minimum of 1-1/2” is needed for most module plumbing and electrical clearance. Note in Photo 3 how the module is recessed into a 1-1/2” tray for overhead clearance.
The outlet of the module is a GM 3/8” quick-connect and sufficient for up to 750fwhp.
VaporWorx has adapters available that will attach to the 3/8” quick connect and convert it to an AN6 male fitting.
Power wiring to the module is done using an OEM style wiring harness. A typical wiring harness can be seen in Photo 4.
A typical fuel line and electrical connection layout is shown in Photo 5.
The 5th-gen LS3/L99 fuel module requires a 15-amp minimum circuit.
In most cases, a relay will be needed to supply sufficient power. A VaporWorx PWM controller (Product Number 66136) will work very well with this pump for up to 550FWHP naturally aspirated. It is not recommended to use the Gen5 LS3/L99 fuel pump in forced induction applications.
It is highly recommended to use the ECM fuel pump control circuit. The ECM will automatically shut off this circuit if the engine shuts off in an accident. Most of the ECM fuel pump control circuits are BAT+ switch, meaning that the circuit connects to BAT+. The relay will need to be wired accordingly.
No additional fuel filters are needed since the final filter is built into the fuel module.
However, it is required that the fuel line from the pump to the fuel rail be thoroughly flushed before engine startup.
Using PTFE flexible fuel lines and stainless hardlines will reduce the chances of hose deterioration and the resulting injector clogging. Modern fuels can be very aggressive on elastomer lined hoses whereas PTFE is impervious to just about anything.
When comparing the cost of a fuel module system vs. a traditional, the costs of un-needed components should be considered.
For example, when using the VaporWorx system, the following components are no longer needed:
1. External filters
2. External pressure regulators
3. Return lines
4. Fittings, mounts, clamps, etc. to connect it all
5. The room all of the above components take
6. The long-term reliability of the components
Over 800 on-track and 3000+ street miles were put on the fuel module during testing.
At no time did the engine suffer due to fuel starvation except when it drained the tank dry on a road racing course.
The same module is still in use today, since 2010, serving well as a test mule for the electronic fuel control systems that will be covered in the later sections.
The key to selecting the correct fuel module is to know what power level it will support.
The following guidelines can be used for gasoline engines:
Note: GM pumps are noted below due to their low cost and are readily available. Ford GT and GT500 pumps are also quite capable.
Naturally Aspirated:
Under 550hp @ 60psi: Gen5 Camaro LS3 fuel module.
Under 775hp @ 60psi: Gen5 Camaro ZL1 fuel module.
Under 900hp @ 60psi: Cadillac CTS-V2 fuel module.
Supercharged:
Under 650hp @ 60psi: Gen5 Camaro ZL1 fuel module.
Under 800fwhp @ 60psi: Aeromotive Super ZL1 (Product Number 68101) fuel module.
Over 800fwhp @ 60psi: KPM1500
For E85 applications, a minimum of 30% additional fuel capacity will be needed for up to 800FWHP. By about 900FWHP more pump gasoline than e85 is needed to help keep intake temperatures cooler.
Note: The Gen5 ZL1 is usually easier to fit since it is shorter and has fewer penetrations on the hat to plug. The Gen5 ZL1 is a great low-cost pump and is recommended for many retro-fits into muscle cars when running on gasoline.
Fuel Flowrate Tables
Fuel flowrate tables for the LS3, Gen5 ZL1, CTS-V2, and CTS-V3 can be found below.
The Aeromotive Super ZL1 has the same flowrates as the CTS-V2.
Note that the BHP values are for a Brake Specific Fuel Consumption of 0.55.
Adjustments according to your engine type should be made.
Camaro Gen5 LS3/L99 Fuel Module
Camaro Gen 5 ZL1
Cadillac CTS-V2 (2009-2014) Fuel Module
Key Comparisons
The overall cost of the fuel system is usually also a factor when choosing they type of system. However, all of the components of a traditional system should be weighed and compared to that of a VaporWorx PWM system.
• No external regulators, return lines, fittings, or fuel filters are needed.
• Extended pump life is expected and reliability increased.
• If big power is in the future, a larger capacity fuel module can be used now with no drawbacks, hence you avoid needing to do the job twice.
• Need even more fuel? The KPM1500 can supply 1000FWHP on e85m plus Aeromotive has even higher horsepower offerings.
Fuel module advantages:
1. Excellent fuel delivery under all conditions.
2. Proven OEM design and reliability.
3. Readily available replacement fuel modules are as close as your GM dealer.
4. OEM wiring and sealed plugs.
5. OEM o-ring seals and cam rings.
Fuel module disadvantages:
1. Initial costs may be higher than other systems.
2. Additional fabrication typically required to get the fuel module into a tank. Custom tanks are readily available for any car.
Continued Reading
This article is part 6 of the 10-part informational series: Fuel Delivery Systems – An Understanding
To continue reading in the series, use the navigation below:
