Fuel Injection System Conversions

Throttle Body Injection (TBI)

For the easiest method of converting a motor to EFI a throttle body is generally the best alternative. Many components are elliminated reducing the complexity compared to MPI systems. The throttle body controls the fuel pressure, fuel delivery, idle air mixture in a single housing with the throttle butterfly and the TPS. A lot of plumbing and work fitting up components to motor is elliminated. In Australia the 1.8 Camira and Nissan Pulsars are a good source of parts for a Delco system to suit any size motor provided a suitable throttle body is fitted. The EA Falcon used a 3.9 litre six with a dual throat TBI system that mounts to most manifolds with a Webber bolt pattern. Custom Engineered Fuel Injection Systems have a very informative site on the Delco ECU providing information, products, technical guides and a manual. This site is a must for anyone attempting to repair, modify or install a Delco EFI system.

Delco EFI relay and MAP sensor.

One of the many Delco ignition circuits.

Multipoint Injection (MPI)

Multipoint injection systems usually require a custom fabricated manifold that accepts the injectors unless a derivitive of the motor being converted can be located. Be very thorough when selecting appropriate parts for a conversion most bits you think should fit won't. Converting a 1.8 Camira TBI motor to MPI became a nightmare when the distributer drive on the cams were found to be different. Swapping the cam, complete with its housing resulted in the loss of all compression. Three attempts later the distributer shaft was cut off with a hacksaw and persuaded to fit, a 10 minute job that could have been done initially except for the desire to do it properly. Manufacturing specifications change during a products life cycle and EFI components are no exception with the possibility of mechanical and electrical changes being made.

Sequential Injection (Port Tuned MPI)

Sequential injection is an advancement on MPI that produces better performance by activating each injector when the inlet valve on the adjacent cylinder is open. MPI opens all of the injectors at the same time or in 2 banks of 2, 3 or 4 injectors and this arrangement is not considered to offer many benifits over TBI. If the expense and complexity of fitting a MPI system can be justified a sequential injection system is the most desirable. Power comparisons between common Australian cars shows models fitted with TBI to produce less power than MPI vehicles and sequential injected is on top in all comparisons made. Always be sure the injectors are the correct size for the type of ECU you are using, sequential injectors flow much more fuel than batched injectors. Be sure when comparing flow rates of the injectors that the data is presented the same. Some report the flow rate at 100% while others use 80% (the maximum recommended duty cycle).

Ford throttle body and TPS.

Volvo hot wire air flow meter.

Modifying and Tuning EFI systems

All open loop EFI systems can be modified cheaply by sourcing parts from other models, altering the signal values from the original sensors or some like the Delco system can be re-mapped to alter the fuel and ignition settings. The web is the best source of information on wiring connections for ECU's and sensors. AEM is a good site to look for information along with others linked below. The Bosch LE Jetronic is another system that has a lot of information available making it an ideal conversion candidate available from many local models worldwide. This unit cannot be re-programmed easily like the Delco ECU but has many adjustments built in to the sensors to allow it to be used on a wide range of vehicles from different manufacturers.

There are 2 types of airflow meters used on the Bosch system, one is a vane type and the other pictured above is hot wire unit. The vane type uses a flap in the air input duct to operate a switch/es that signal the ECU. A hotwire is a heater element in the air intake duct that varies its resistance according to how hot it is ie. more air = less temp = different resistance signal to the ecu. The 2 types are not interchangable but various sizes and configurations exist for each type. The vane type is the better choice to tamper with allowing the preload on the flap to be altered. Less spring pressure results in more fuel and less fuel is delivered when the spring pressure is increased. This system allowed easy adaption to the requirements of different engines making it ideal for tinkerers. Resistors can be connected to water temp sensors to alter fuel ratio's over the rev entire range. A higher resistance (add a resistor in series) increases richness and a lower resistance value (add a resistor in parallel) leans the mixture.

Fuel injectors with a different flow rate and altering the fuel pressure are 2 other methods of adjusting the fuel ratio if suitable parts can be located. Jetronic Fuel Injection    Kalmaker Fuel Injection    EFI Applications PDF These links were found to be useful for the projects I have undertaken and should provide links to all of the information needed by anyone else keen enough to have a go.