Current EFI systems use rotary electric fuel pumps to deliver fuel to the engine - all pumps use a simple, permanent magnet, direct current (DC), series wound, wet, electric (not electronic) motor driving an incorporated mechanical pump to produce a fl ow of fuel. This description is also true for in-tank pumps found on carburetted vehicles. The pressure in a fuel system is created by the restriction of the fuel pressure regulator in EFI systems and by the needle and seat, or return line restriction, in carburetted systems. The higher the pressure (greater restriction), the lower the fuel fl ow and vice versa.
All current rotary pumps are “wet”, i.e. the fuel is circulated through the pump motor to lubricate it and to dissipate the heat created as a consequence of converting electrical energy into mechanical energy. Fuel is a poor conductor of electricity and has no effect on a pump’s electrical operation – as the fuel is far too dense to allow combustion, fi re or explosion is not, except under extraordinary circumstances, a hazard.
A spring-loaded pressure relief valve is incorporated into all high pressure pumps to prevent the motor stalling (and consequently burning out) if a suffi ciently high restriction should occur on the outlet side of the pump, e.g. a blocked fuel fi lter. If a suffi cient restriction occurs, fuel is internally re-routed to the pump inlet and recirculated through the pump on external (line) pumps, and out of the pump on in-tank (submerged) pumps. Low pressure peripheral style in-in-tank pumps generally use a bleed hole (or holes - usually under the electrical terminals), rather than a spring-loaded valve, for the same purpose.
EFI pumps are not considered to be electronic – the only electronic, or solid state, components generally used in them are resistors for radio frequency interference (RFI) suppression.
All pumps are very “voltage sensitive”, i.e. the lower the voltage of the power supply, the lower the pump performance - a typical large in-tank gerotor EFI pump, at 300 kPa pressure, will fl ow 155 to 205 L/hr at 15 VDC, 130 to 180 L/hr at 13.5 VDC and only 5 to 55 L/hr at 7 VDC.
Under normal circumstances, the life of a pump is determined by the motor’s brush (and to some extent commutator) life - generally between 2000 and 4000 hours. Premature failure of a pump is usually caused by fuel contaminants – very fi ne abrasive particles (sediments), gum residues from oxidised fuel, phenolic residues (either as a fuel anti-ageing agent or as a result of under-refi ning fuel) and/or asphaltenic material (micron or sub-micron particles of carbon with a resinous coating; a not uncommon fuel impurity similar to phenolic residues).
The differences between pumps are mainly in the type of pump and the style of pumping element employed - there are only two types of pump although there are several styles of each type:
• Positive displacement type EFI high pressure pumps use rollercell (or rollervane) or gerotor pumping element styles.
Positive displacement pumps are also used for aftermarket high fl ow/low pressure performance applications.
• Non-positive displacement type low and medium pressure pumps use peripheral or centrifugal pumping styles whilst high pressure pumps use a turbine style pumping element. Non-positive displacement type in-tank pumps are also used for carburetted applications.
Positive displacement? Non-positive displacement? Consider a bath full of water - displacing the water using a bucket is positive displacement – trying to do it with a sweeping arm movement would be non-positive displacement - you could do it if you could move your arm fast enough, often enough, for long enough!
Positive displacement pumps are more susceptible to fuel contamination problems, both solids and residues, because of their smaller running clearances (down to 1.2 µm: a human hair is around 76 µm!) and are now less popular than non positive displacement pumps.
For the metrically challenged, the following conversions should sort out the measurements (in bold) used:
1 µm (micron) = 0.001 mm (millimetre) = 0.000039 in (inch) 1 mm = 0.039 in
1 mb (millibar) = 0.1 kPa (kilopascal) = 0.0145 psi (pound per square inch) = 0.03 in Hg (inch of mercury) 1 kPa = 0.145 psi
1 gm (gram) = 0.0353 oz (ounce)
1 L (litre) = 0.22 imperial or 0.264 U.S. gal (gallons) - also used for fl ow:
1 L/hr (litre/hour) = 0.22 imperial gal/hr or 0.264 U.S. gal/hr (gallons/hour) For fl ow/minute, divide hourly rate by 60 1 kW (kilowatt) = 1.34 bhp (brake horsepower)
VDC = volts direct current
FUEL PUMPS
Early EFI pumps were externally mounted (in-line) rollercell, or rollervane positive displacement types with very small pumping element clearances - side clearances typically as small as 1.2 to 6.3 µm – with a consequent low tolerance to solid fuel contaminants, i.e. dirt!
Rollercell pumps are a variation of rotary vane pumps, with rollers in place of sliding vanes creating the “cells” to fl ow the fuel, hence rollervane.
EXTERNAL ROLLERCELL PUMP
The fi rst mass produced EFI equipped vehicles used paper element fi lters of 10 to 15 µm media pore sizes between the tank and the pump, but the later systems relied on a one or two layer woven plastic screen, or strainer, generally having pore sizes from 60 to 80 µm. Typical external rollercell pump speeds are around 2500 RPM.
To overcome problems handling hot fuel vapour and aeration, the dual or twin pump system evolved. In this arrangement, a low pressure, non-positive displacement, generally peripheral, style pump was submerged in the fuel tank to prime, or feed at a positive pressure, the (still externally mounted, still rollercell) high pressure pump.
PERIPHERAL PUMP
Peripheral style pumps were used because of their greater ability to separate vapour from hot fuel: air, in any form in a pressurised EFI system is intolerable – the fuel (a liquid) will be pressurised, whilst any air (a gas) will be compressed, affecting the system pressure. Since the amount of fuel injected into the engine is determined by the “injector open” time (pulse width) at system pressure, any air in the system will cause a mixture leanness.
Vapour in the fuel of an EFI-equipped vehicle has several potential sources – the heat generated in the fuel pump, radiated and conducted engine and underbody heat, and ambient heat. Vapour may also be generated in the fuel return line: as the fuel passes across the pressure regulator valve - it drops from system pressure, generally between 200 and 350 kPa, to almost atmospheric – this rapid drop may be enough to cause vaporisation.
Dual pumping element peripheral pumps are also used on throttle body injection (TBI) systems and as pre-pumps – earlier pumps for carburetted applications were either centrifugal or single pumping element peripheral styles, but turbine style pumps are now more common.
Some early EFI-equipped U.S. vehicles were originally produced with just a single, external high pressure pump, but vapour problems associated with hot fuel led to the introduction of an in-tank centrifugal pre-pump as a service fi x. Centrifugal pumping elements are not as effective vapour separators as peripheral styles.
CENTRIFUGAL PUMP
FUEL PUMPS
Peripheral pumps employ end clearances of around 44 µm – with centrifugal pumps having even larger clearances, neither are prone to major contamination-related problems, but excessive quantities of fi ne contaminants cause wear which reduces their performance and life.
In-tank, or submerged, fuel pumps are not new, having been used on World War II fi ghter aircraft: with their ever increasing G-force loadings, they needed a positive fuel supply from the wing tanks.
AC in North America offered substitute in-tank pump assemblies for trucks in the 1950s and original equipment supply for passenger cars began in 1957.
And in England, Lucas supplied the in-tank pumps fi tted to E Type Jaguars in 1961. The fi rst application to use a pump which we would recognise today (much the same as a GE015) was the 1969 Buick Riviera.
Pumps next reverted to being a single high pressure item, but this time in-tank: initially a large (52 to 61 mm diameter) rollercell pump without a peripheral fi rst stage, then either a small (37 mm diameter) rollercell pump or a large (43 mm diameter) gerotor pump; generally with a peripheral fi rst stage to remove vapour from the fuel before it enters the pump’s high pressure pumping element.
IN-TANK ROLLERCELL PUMP
A variation of the standard small in-tank rollercell pump is the variable speed, or two-speed, rollercell pump. This type of pump incorporates a neodymium iron boron (NIB) magnet material (also known as “Magnaquench”) which, because it is considerably magnetically stronger than conventional ferrite material, allows the magnets to be reduced in thickness and the armature to be increased in size (and power), thereby retaining the same overall dimensions.
During low speed/low engine power operation, power for the pump is supplied through a resistor, reducing the voltage and pump performance – the resistor is bypassed for high speed/high power operation. Current draw at maximum performance on this style of pump is typically twice that of single-speed pumps – 10 to 13 amps versus 5 to 7 amps.
Large in-tank rollercell pump speed is typically the same as the earlier external pumps (2500 RPM), whilst a small rollercell pump speed is typically 4000 RPM - generally, the smaller the pump the higher the speed.
And the unit built into the outlet moulding of some large in-tank rollercell pumps, with the diaphragm housing on one side? It’s a pulse damper – the fi ve pump rollers form “cells” which may impart unwanted pulses to the fuel, upsetting injector fl ow. Pulse dampers are also fi tted in the fuel line between the (high pressure) pump and the engine – on CIS systems they’re called accumulators. Gerotor pumps may use pulse dampers as their pump lobes also form cells.
Note: A pulse damper fi tted to a fuel rail (at the engine) serves a different purpose to a damper fi tted at or near a fuel pump – a rail-mounted damper is used to overcome pulsations created in the fuel rail by the alternate opening and closing of injectors, even with turbine pumps.
GEROTOR PUMP
Gerotor (gear and rotor) pumps were developed as a quieter positive displacement alternative to rollercell pumps, although they are twice as susceptible to dirt-related problems as rollercell pumps. They are also more easily affected by the gum residues formed in oxidised (stale) fuel as a result of improper use of dual fuel vehicles and which prevent effective pump lubrication, particularly between the cam ring and housing. Strainer pore size on some applications are reduced to around 30 µm, but most common pumps still use 40 to 80 µm. The large gerotor pumps typically spin at around 4400 RPM and small gerotors at approximately 4800 RPM.
Rollercell and gerotor pumps are used on both multi point injection (MPEFI) and TBI systems.
FUEL PUMPS
Small gerotor pumps were used extensively in the U.S., although some early Korean cars are the only volume selling vehicles seen in Australia with this pump style. Some European car companies persist with this type of pump.
Uprated small gerotor pumps are also used as variable, or two speed, pumps.
Small (36.5 mm body diameter) gerotor pumps seen in Australia do not have a peripheral fi rst stage and can be notorious for their poor hot fuel handling performance.
Another pump type introduced in Europe in the early 1990s is the rotary screw, in which a contoured screw rotates in a housing, much like a screw-type supercharger. Whilst very quiet in operation, rotary screw pumps also rely on miniscule clearances, with their inherent intolerance for dirt, for effi cient operation.
Meanwhile, a pump developed from the earlier peripheral non-positive displacement pump style had leapfrogged the dual pump stage - the turbine, or regenerative, pump. First employed by Japanese manufacturers in ‘side-outlet’ TBI pumps and later, in 51mm diameter form, turbine pumps have now become the most commonly used pump style. It was refi ned in 1989 with the release of a much smaller (38mm diameter) and, more importantly, lighter version. Because of the pump’s turbine action, it is very good at removing vapour from hot fuel. Problems associated with dirt and oxidised fuel are also less with this type of pump as it utilises (relatively) larger clearances in the pumping element.
TURBINE PUMP
Turbine pumps are used on MPEFI and TBI systems - low pressure versions are used on carburetted applications.
Strainers are generally 40 to 60 µm pore size, although some as small as 20 µm have been used. Typical pump speeds are 5800 RPM (large turbine) to 7000 RPM (later small turbine). Turbine pumps are also used in two-speed systems.
A variation of the turbine style of pump is the side-channel pump. Unlike the traditional turbine style pump where the vanes are on both sides of the outer edges of the impeller and the fuel fl ow channel is around the circumference of the impeller, in the side-channel pump the vanes and fuel fl ow channels are within the impeller circumference and fuel fl ows through the impeller. Side-channel pumps have greater effi ciency and are able to provide the higher system pressures – currently up to 450 kPa - required for modern EFI systems. Side-channel pumps may look exactly the same externally as their turbine counterparts.
A note here on replacing a pump with a different pumping type/style item: don’t do it unless you know it works! All pumps emit some noise and different types of pumps emit different types of noise. To complicate the issue, there are two potential noise sources to contend with - vibrational and acoustic (sound) - both determined by the pump’s operating frequency and both modifi ed by the transfer medium, i.e.
solid (bracket, isolators, hoses, seals, etc.), liquid (fuel covering the assembly) and air (low fuel situation).
A positive displacement small gerotor pump with a rotational speed of 4300 RPM emits a quite different type of noise to a non positive displacement small turbine pump spinning at 7000 RPM.
The pump mounting (pump bracket, tank seal and even the tank mounting) and pump isolation (rubber isolators, hoses and even the pump sleeve, if fi tted) are all designed for the type of pump used. Unless these components are modifi ed or changed, using a positive displacement (e.g. gerotor) pump to replace a non-positive displacement (e.g. turbine) pump will create a noisy installation.
At the same time as pumps were being improved, changes were being made to the remainder of the fuel supply system.
Return lines began to be incorporated into the pump tank unit so that the clean, pre-fi ltered fuel could be directed at or near the pump strainer/inlet.
The bracketry to which the pumps are mounted have become more lightweight with the lighter pumps – steel initially, but now frequently plastic. By mounting the fuel gauge sender unit on the pump mounting bracket, one tank unit instead of two is needed and generally the whole fabricated bracket and pump assembly has been replaced by a fuel pump module assembly, with a built-in swirl pot or reservoir.
FUEL PUMPS
Early fuel pump modules were merely a conventional pump within a container attached to the tank aperture fl ange - a sort of detachable swirl pot. Current versions use either a separate, pump outlet fl ow-operated auxiliary “jet” pump, or the fi rst stage of a two stage pump, to prime the module cavity – the second stage produces the fl ow for the engine. Some modules use fuel pumps with built-in jet pumps operated by partial fl ow from a single pumping stage.
Jet pumps work on the same venturi principle as carburettors – as a controlled fuel fl ow passes through the jet pump venturi, it speeds up and produces a pressure drop at the end of the module inlet passage (located near the venturi’s minimum diameter), drawing in fuel. Jet pumps are also used to transfer fuel from the reservoir side of a “saddle” type fuel tank, generally fi tted to four wheel drives, to the side containing the main fuel pump.
Fuel pump modules may be spring-loaded between the pump housing and the tank sealing fl ange to keep the inlet on the bottom of the tank. A module of this type uses either rubber buffers to cushion it against the tank bottom, or a rigid strainer with a raised plastic moulding on its underside, to keep the strainer surface off the tank bottom. Some fuel pump modules are remotely mounted from the tank aperture fl ange and connected only by hoses and electrical wiring – the module itself is fi tted onto a bracket on the tank top, bottom or baffl e.
Fuel pump modules may be “open” (unpressurised container) or
“closed” (pressurised container). A non-return inlet valve is fi tted to the bottom of the container to maintain fuel in the container whilst the vehicle is parked and to allow the container to fi ll when replenishing an empty tank. A non-return valve is also fi tted to the inlet of a two stage pump.
The strainers used on fuel pump modules may be moulded or woven types, depending on manufacturer.
Strainers may be duplicated - one on the module inlet and one on the pump inlet - up to four strainers may be used on current applications; the extra ones for the jet pump and return.
TYPICAL MODULE – FUEL FLOW
MODULES
Many vehicles are now fi tted with “returnless” fuel systems where the pressure regulator is integrated into the tank module. Two types of these systems are now in use:
• With the pressure regulator placed between the pump outlet and the external fuel fi lter - the potential drawback of this system is that the fi lter will become more restrictive over its service life, with a potential system pressure drop at the injectors at high fl ow rates.
• With the pressure regulator placed after the fi lter – irrespective of the fi lter’s restriction/pressure drop, the regulator will maintain the same system pressure at the injectors. This type of system may have
a) a fi lter with a service life of 80,000 to 210,000 km integrated into the pump module in the tank, or
b) a conventional fi lter mounted adjacent to the tank, with a short line from a T- or Y-piece after the fi lter (engine side) back into the Fuel pump modules are made in a variety of confi gurations and may incorporate any pump type and style, but all share the same purpose:
to ensure the quality and quantity of the fuel available to the main system fl ow pump.
By routing the return line (with its clean, pre-fi ltered fuel) into the module cavity, the quality of the fuel supplied to the pump is greatly improved. And by containing the slightly hotter return fuel in the module, the greater quantity of fuel in the tank remains cooler, reducing evaporative emissions. By consistently maintaining an adequate quantity of fuel to supply the pressure pump, engine performance problems associated with fuel surge on corners and inclines is prevented, and the tank doesn’t have to be as extensively baffl ed.
FUEL PUMPS
The main advantage of returnless systems is the reduction – by up to 10 C - in fuel temperature in the fuel tank, reducing fuel vaporisation by approximately one third and thereby reducing potential evaporative emissions as legislative regulators impose ever more stringent emissions requirements.
By integrating the fuel pump, jet pump, pressure regulator, main fi lter, and fuel gauge sender unit, if possible, into one compact unit within a plastic fuel tank, vehicle manufacturers are able to maximise the fuel system effi ciency whilst minimising emissions and reducing costs.
INTEGRATED IN-TANK PUMP UNIT
The unit above is fi tted into a “saddle” type fuel tank and uses the transfer jet pump (8. in the left illustration; 14. in the right) to draw fuel from the opposite side of the tank in low fuel situations. The pipe (7. in the left illustration) must be disconnected for module removal, and reconnected when refi tting the module. The fuel fi lter is replaced every 210,000 km.
Like several other vehicle systems, fuel supply system design has moved toward the use of pre-assembled modules that can be quickly fi tted to a vehicle in production. Modular vehicle assemblies now include:
• Instrument panel, or complete dash assembly
• Inlet manifold, throttle body, fuel rail, injectors, sensors and associated components
• Fuel tank, fuel pump, fuel fi lter, fuel pressure regulator, fuel gauge sender and associated components
This method allows a module to be simply bolted to the vehicle and connected – usually with quick-connection fi ttings - to the relevant vehicle (usually semi-rigid plastic) pipes and electrical systems.
Developments in fuel pumps have included:
¾ The development of pumps able to effectively operate in a variety of “biofuel” fuel blends. This is achieved by the use of more compatible
¾ The development of pumps able to effectively operate in a variety of “biofuel” fuel blends. This is achieved by the use of more compatible