Joined: 22 Jun 2006
this is the beginning of explaining the original MPI injection that came with the 4G63 turbo engine, by no means is this a complete explination, but I hope you can help me explain it by asking the questions you have
this is a very general explinaion
I guess the place to start is the main relay, its is the power distribution center of the whole system
before OBD1&2 all the manufacturers had a free hand on how to do things, some came with serial data, some didnt, the reason that is important is because you need serial data to build a scanner tool like we have today, so in the early wild days of computer design, we had to train to use the power distribution schematics to repair fuel injection problems
this is the main relay schematic with the key off and 'at rest'
this is the main relay with the key in start position
and this is the main relay with the key in 'run' position
there are 4 things needed to happen to make the engine run ( you can count that on one hand!)
you need air/fuel mixture intake, you need compression, you need ignition (spark) and you need timing, so I guess we should break down just the ignition
This is the CAS
all it is is a camera, really, two light emmiters are in the plasitc housing, the disc rotates between the two light emmiters and two photo diodes, the windows in the disc turn the photo diodes on and off by allowing the light to shine through the windows
I originaly thought this may have been a hot wire set up but I stand corrected, it is a korman votex set up
Some early Mitsubishi models also used the KV sensor. Ultrasonics (sound waves with a frequency higher than the human ear can hear) are used to detect the pressure changes. A small speaker sends a fixed ultrasonic tone through the vortex area of the sensor to a microphone. The greater the number of vortices, the greater the turbulence and the more the tone is disrupted before it reaches the microphone. The sensorís electronics then translate the amount of tone distortion into a frequency signal which indicates air flow.
The 1983 Ė 86 Mitsubishis have a four-pin connector and the 1987 to 1990 versions have a six-pin connector. The early units also contain an integral air-temperature sensor while the later ones also have a built in barometric-pressure sensor. From 1991 onwards Mitsubishi started using a redesigned KV sensor with an eight-pin connector which replaces the ultrasonic generator with a pressure sensor which measures fluctuations in air pressure directly.
the is a barometer to sense the altitude and air temp sensor to adjust for hot and cold air
The air flow meter is just that; itís not an air mass meter - it needs other sensors to gain information on air density and temperature so the ECU can make the necessary compensations. An air temperature sensor is fitted inside the Karman vortex air flow meter, but it is absolutely nothing to do with the meter itself.The system also uses a barometer ( high alititude sensor). The frequency of the Karman vortex square wave varies according to the density of the incoming air and for altitude using the barometer
and last but not least there is the injectors themselves, after all the inputs are made to the ECU, information is computed into the proper injector pulse width, the injectors are preset in size by how many pounds per hour of fuel the injector can pass into the cylinder, but to correct for engine load and speed, the ECU controls how long to hold the injector open by using a bianayr number to switch the injector on and off
I will be posting how to test and understand all these pieces with hand held, low buck tools if anybody is intrested
Joined: 13 Jun 2009
Location: Columbus, Ohio
The MAF isn't a Hot Wire setup, it's a Karman Vortex type. The Honeycomb is used to straighten the airflow past the sensor which then it is disturbed by the sensor behind it. the sensor then looks at the vortices it caused and counts them with sound waves. The sensor then sends a square wave frequency representing the airflow.
That's the simple description.
Also, on Distributor based motors (4G64 Truck Motor) the CAS is built into the base of the distributor. wiring is the same.
I converted my 4G64 Truck motor to a dual coils setup like the 2.0 so I could use a AEM Plug and Play Fuel Computer...you also have to change the Throttle body, Ilde air controller motor is different also.
but enough thread jacking, back to the original topic.
_________________ Mike M.
ECTA Record Holder/Bonneville Record Holder
Wow, great writeup! Thank you. I know that the ECU/Harness gets all its power from the MPI relay but hooking into the MPI relay from the stock stuff was sort of a gray area for me. This helps tremndously!
Joined: 22 Jun 2006
before scanners were developed to work with serial data,we had to use hand held votage meter with a firm understanding of how to read scematics and what the different volages were telling us
Scematic's by themselves were no good without understanding how to use them, they are maps, really, showing the trail of voltage
Voltage is not the only force working on the relays and wires , but with ohm's law, you can find the other numbers for resistance and amps, its just easier to find the voltage number
If you think of the voltage as 'pressure' pushing the electrons down the wires, then think of the voltage meter as a pressure guage, you can imagine the wires are tubes filled with fluid moving towards ground as a final destination
this is only the fuel injector/ECU side of the main relay, the same exact proceeure is used on the fuel pump side of the main relay also
Joined: 22 Jun 2006
did you ever build a telegraph key when you was a boy scout? I did, we used a nail, with wire wrapped around it and a small strip of sheet metal near the nail, when we closed the switch, battery voltage was grounded through the fields of the wire and made the nail a magnet for the metal strip causing a buzzing niose to occur, well, that is all a main relay is
here you can see a 'hand off' of power within the relay, controled by the ECU . It exchanges power feeds to the fuel pump from the primary starter side to the ign 'run' side
Wow, great writeup! Thank you. I know that the ECU/Harness gets all its car navigation system power from the MPI relay but hooking into the MPI relay from the stock stuff was sort of a gray area for me. This helps tremndously!
Hey you seems to be an experienced person. I am thinking of designing custom race car. Will you handle my entire project.
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