Tag Archives: electronic fuel injection

Rover Mini MPi Inlet Manifold and Throttle Body

I’m embarking on a project to fuel inject my 1987 Austin Mini, which has already had an engine swap from a 998 to a 1098, but currently runs on an HS4 1.5″ single carburettor.

This obviously offers a reasonable level of tunability, with the ability to change needles, dashpot damper springs, dashpot oil and mixture adjustment and is relatively easy to set up for quite a reasonable state of tune, especially now that I have an AFR meter installed.

However, I would like to try fitting an MPI system and develop my own ECU for electronic fuel injection. Due to the ‘Siamese ports’ on the A-Series engine causing charge robbing, and only having one fuel injector per two ports, this is apparently something that’s difficult to achieve well, which makes me want to do it all the more.

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What does a Manifold Absolute Pressure (MAP) sensor do?

Manifold Absolute Pressure (MAP)/ Manifold Pressure sensors are used to determine the pressure of the air inside the inlet manifold, just before it enters the engine inlet ports. This is generally measured between the Throttle Body and the intake ports on a naturally aspirated engine, and between the turbocharger compressor outlet (after the Intercooler) on turbocharged or supercharged engines.

GM Manifold Absolute Pressure sensor

GM/Bosch Manifold Absolute Pressure sensor

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Video Explanation

I’ve made a video of the whole system explaining all of the sensors, actuators and interfaces, and some of the more advanced indicating equipment that I’m using.

A more detailed explanation of the closed loop ignition timing control is given here: http://scottsnowden.co.uk/?p=341

Adding a load

More progress made today, I connected up the alternator to the engine to begin testing it under load. This was pretty successful, and the ECU all performed as expected, with only a few tweaks to the PID controller parameters to improve the AFR control. I restricted the range of fuelling down to as restricted as possible to prevent the system setting wildly large or small fuelling amounts under certain conditions. I finally managed to get the PID to maintain the AFR slightly rich within a few percent under steady state conditions.

Belt drive to alternator

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Fuel injection map and closed loop lambda feedback

I have now managed to successfully map my engine simulator for the fuel injection timings across all loads and engine speeds. I have set up a two dimensional array, of speed and throttle position, and inside each element is the time in microseconds (us) that the fuel injector should be open for. I’ve also added closed loop lambda feedback.
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