Learning about Fuel Pumps
All modern EFI systems use electric fuel pumps.
Even Direct Injection engines need a “low pressure” lift pump to feed the high pressure engine mechanical pump.
These low pressure lift pumps in and control systems are for practical purposes the same as the pumping systems used in modern port
injection (LS3, LT1/4/5, Coyote, GT500, GT, Demon, Hellcat, Hemi, etc.) Even the mighty MOPAR Hellephant crate engine comes with a pulse width modulation fuel pump driver. There seems to be a trend here by some of the smartest engineers in the automotive industry. But, we’re getting ahead of ourselves……
Electric fuel pumps have proven to be safe and reliable.
Many OEM’s offer 100,000 mile warranties
that include the fuel systems on today’s cars. If it’s good enough for that type of warranty, then they must be very reliable if they are properly fed.
The two most popular types of electric fuel pumps are the in-tank and in-line types.
The in-tank pumps used by many aftermarket tank manufacturers are typically used in a pump-on-a-stick arrangement like that in Photo 1.
The pump is held to the stick/tube/support method, and the fuel line outlet, by a short piece of hose and some clamps. Often the bottom of the pump is supported with a method to secure it to the return line which may act as a return tube.
An EFI high pressure in-line pump is just as the description implies:
Install the pump in-line external to the fuel tank. In this arrangement the fuel should be gravity fed to the pump inlet. Electric vane and turbine pumps are not good at suction, and when asked to lift fuel out of the top of the tank, it may lead to poor pump performance. For sure if the pump is lifting fuel it will not work well at a reduced speed. An example of an in-line pump can be found in Photo 2.
Though the thought of an inline pump may be attractive, there are drawbacks. First, lifting from the top of the tank puts the fuel under suction. If fuel that is already hot has suction applied it will be more susceptible to boiling. It’s the opposite of putting a pressure cap on a radiator which raises the boiling point. So, hot circulated fuel under suction
will more easily boil and cause vapor lock.
Second, if an inline pump is used it should be gravity fed. That means taking fuel from a sump (to reduce slosh effects) to feed the pump that should be lower than the sump. Pretty soon the pump is the lowest part of the car.
Oh, and exactly zero modern cars have inline pumps. Those really smart OEM engineers might on to something again.
For both the in-tank and in-line arrangements the pump or pickup can be placed in a sump.
A sump is a section that has been lowered relative to the normal bottom level of the tank. The sump is usually added to try and provide a method to control fuel slosh under less than full fuel load conditions. A basic
illustration is shown in Diagram 1.
For an electric fuel pump to have long life it must have a constant supply of fuel. Fuel is the life blood of the pump.
The fuel acts as a lubricant and as a means of removing heat. If the fuel sloshes away from the pump then its source of lubrication and coolant goes away as well.
Once the liquid fuel lubricant and coolant sloshes away, increased friction and heat occur in the pump.
With increased friction and heat comes accelerated wear. If the pump is subjected to this condition, premature pump failure will occur.
Once this damage condition occurs it is only a matter of time before the pump fails. It may be months later depending on how much the car is driven, and one may have forgotten the initial failure mode.
Sump advantages:
- Low cost.
- Offers better fuel control than just a flat-bottom surface.
- Can be made into a variety of shapes.
- Can have the fuel outlet and return in a non-traditional location.
Sump disadvantages:
- The fuel pump is not completely immersed in fuel / low pump inlet head pressure at low liquid levels.
- Fuel slosh can still occur under braking and cornering when fuel levels are low.
- For some it may not be aesthetically pleasing.
- Ground clearance may be a problem.
- Exposed fuel lines may be subject to road damage.
An external surge tank is another method to help reduce the effects of fuel slosh.
Surge tank designs use one electric pump in the main tank to feed a smaller second tank.
The smaller second tank also has an electric pump(s) which feeds the engine, and due to its small size and narrow shape, the effects of fuel slosh are low.
There is a return line from the surge tank to the main tank, and a return line from the pressure regulator to the main tank. A surge tank system can be found in Diagram 2.
Surge tank advantages:
- Main fuel tank slosh effects minimized.
Surge tank disadvantages:
- Two pumps.
- The pump in the main tank is subject to damage under low-fuel conditions.
- Double the amount of plumbing, fittings, wiring, and power requirements.
- Difficult to fit the surge tank in many chassis designs.
None of the above systems are “returnless.”
All mechanically regulated systems have some type of fuel return.
For a true returnless system using brushed type fuel pumps, an electronic pressure-sensitive feedback system combined with Pulse Width Modulation (PWM) must be used.
The primary thing to remember about an electric fuel pump is that its life – and the proper function of the engine – is dependent upon getting a reliable source of fuel at all times, and minimizing how hard to run it.
Vane vs. Turbine style fuel pumps:
For most automotive use, electric fuel pumps fall into two categories: vane and turbine.
In general, vane pumps may not work well with PWM controllers in a returnless system.
Turbine style pumps can often be used in PWM control systems, but validation testing should be done.
VaporWorx has tested and confirmed that the following brushed pumps can be controlled using the VaporWorx PWM controller with a small amount of fuel bypassed for smooth pump operation:
- Aeromotive Stealth 340 (single, dual, and triple) + all Phantom systems
- DeatchWerks, all brushed pumps.
- AEM320 (single, dual, and triple)
- TI Automotive (Walbro) 450lph ‘267 (single, dual, and triple)
- TI Automotive (Walbro) 525lph ‘285 (single, dual, and triple)
- TI Automotive (Walbro) 535ph ‘285 (single, dual, and triple)
Photo 3 shows a modern turbine style pump. Note how the fuel flows around the motor section of the pump to provide both lubrication and cooling:
For PWM to work in a returnless system a small amount of fuel must be bypassed at all times in order to avoid a condition where the pump “chugs.”
In the OE applications, this bypass fuel is used to drive the jet pumps. There’s much more on the jet/venturi/suction pumps and how they work coming up soon.
In the case of the above pumps a small bypass hole that allows some fuel to move at all times is needed. Usually a 0.020-0.041” restrictor will work (please consult Aeromotive on your application).
On aftermarket hat/hangar assemblies that have a jet pump, such as the twin TI 450lph hat/hangers for the Pontiac G8 and CTS-V2, this bypass may be sufficient. Not all pumps are created equally. During testing some 450lph pumps PWM controlled better than others. For the 450lph pumps, having a bypass of 0.041″ diameter has shown to cover all known instances, and 0.051” for the big TI Automotive 525lph pumps.
How big is too big for the fuel pump?
A car that has a 500hp engine will not make any more power if a fuel pump capable of supplying 1500hp is used.
An excessively large fuel will create excessive heat, and that heat ends up being soaked up by the fuel in the tank.
The best thing to do is try and match the fuel pump to the requirements of the engine, and then add 15-20% extra for safety.
However, as will be shown later, the beauty of PWM is that if there is a chance that more power will be needed later, a larger fuel system can in installed now with no fuel system performance drawback. In other words, get the fuel system that is needed for the future without worries of overheating the fuel.
Continued Reading
This article is part 3 of the 10-part informational series: Fuel Delivery Systems – An Understanding
To continue reading in the series, use the navigation below:
