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MPi (Multi Point injection) Info and Faults

MPi distributor

Trick title - there isn't one. It's a twin wasted spark system.

The ECU provides the timing for the spark which it calculates from a bank of stored values it keeps in it's memory. In some MEMs equipped cars it also uses a knock sensor to detect when the timings wrong. In the MPi it just uses the values it has stored.

With the wasted spark system the ecu fires the plugs 8 times during one engine cycle, so each plug fires twice per cycle, one spark being wasted as it fires on the exhaust stroke.

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Why does an MPi feel like it has more torque?

At very low revs the MPi can feel torquier because the ECU has load compensation/idle speed regulation, ie, it'll automatically apply throttle if idle revs drop, making for easier starting.

Also, the injectors sit right in the middle of each of the two inlets, aiming dead centre from the top of the inlet, about half a cm away from the edge of the cylinder face. The inlet is quite long in comparison to the carb-equipped Minis: the inlet on the carbs tend to have to curve up and round to meet the face of the carb, with the carb being sat at the end of the inlet. However, the MPi has the inlet right to the back then the air intake and stuff sat on top.

The longer and straighter the inlet (within reason), the more torque is produced.

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MPi/Spi emmisions... MOT fail?

There's plenty to go wrong with emmisions, there are two common faults that
I know with the SPi, I'm pretty sure it's the same with the MPi.

Coolant Temp Sensor. This acts like a 'choke', it senses the temp of the
coolant and alters the fueling, if this is knackered, then the car will run
rich, causing emmisions problems. When I was building my Mighty Mini, it
was 6 times over the legal limit, it was the coolant temp sensor.

Vacum pipes. These are very dodgy and probably the most common cause of
emmisions and bad running, if they are on too tight, the vacum don't work,
also the collars split and the pipes sometimes burn on the manifold.

Look for the simple stuff before messing with the expensive stuff, cat and
lamda sensor as these are often blamed, but not the problem.

Info form Craig: IME'd 20 Dec 2002

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1998 MPi cooper cutting out on idling/coating.

Problem: Whilst driving it will occassionally just cut out whilst idling. Or sometimes when I have been coasting (still in gear, i.e. foot off throttle) and then go to accelerate again.

Solution from Adrian Taylor added 29 12 02 :

Sounds very much like the IACV to me - I've driven 2 cars with similar symptoms, IACV was replaced in both cases.

Rover finally have quoted me 500 to change both the Idle Air Control Valve (IACV) which they say (although not on paper, only by one of the service engineers) is sticking occasionally, and the ECU itself, and even then they are not sure this would work.

The IACV can be removed and cleaned up, I believe.

I'm told that actual part is about 90 from Rover, fitting should be minutes...

Rover maintenance manual states 0.30 hours.

As for the ECU, they're reprogrammable, and a Rover dealer should be able to either plug in their Testbook computer and tell you whether it's working correctly, or swap one from another car temporarily to see if it cures the problem.

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