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Mpi Ecm Woes

electrical

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#1 mpialan

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Posted 06 July 2019 - 04:52 PM

Until recently my MPI was fitted with a SC Injection Kit, The car was running, but was very rough, running very rich and was a bit of a dog, Despite trips to a number of tuners no one could get it running as I would like.

 

In desperation, I made the decision to revert to the Rover set up. I bought an ECM off eBay (to replace original defunct ECM) and sent it away to have it checked over and have the immobiliser function removed. The ECM came back with a clean bill of health.

 

Having fitted the Rover set up the car will not start. I believe that the MEMS Relay is not energising. The Workshop Manual states the following:

 

MEMS ECM

The ignition sense of the ECM receives battery voltage from fuse A4 in the

passenger compartment fuse box on a W wire provided the starter switch is in

position II. As a result the ECM supplies an earth from the main relay control on

a WK wire to one side of the main relay coil (within the MEMS relay module).

Since the other side of the main relay receives battery voltage on an N wire from

link 4 in the engine compartment fuse box, the relay will energise switching

battery voltage via the relay contacts on an NK wire to the injector(s), purge

valve, stepper motor, ignition coil, manifold heater (Japan only) and positive feed

to the ECM.

 

The ignition sense on the ECM receives 12 volts, however, I do not believe that the ECM is providing an earth to the main relay in the Relay Module. I have continuity on the WK wire.

 

How can I test that the main relay coil is receiving an earth? from the ECM?

 

If the ECM is not providing an earth, why?

 

I have an old MEMS Relay module that I have opened up. By manually operating the various relays I can get the engine turning over, fuel pumping, and a spark, which suggests to me that the ECM is not controlling the various functions?

 

Please keep answers to the basics, electrics frighten me at the best of times and, at the moment my brain is in meltdown.

 

Please, no one suggest that I revert to the SC Injection Kit, I might just cry!

 

 



#2 Steve220

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Posted 06 July 2019 - 05:17 PM

Did you send the ECU off with the 5AS unit for pairing?



#3 mpialan

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Posted 06 July 2019 - 05:48 PM

Yes the 5AS was sent off with the ECM. I had assumed that the 5AS would no longer be required as the immobilser function on the ECM was disabled. However, just in case the 5AS completes the electrical circuit I have fitted it anyway.



#4 genpop

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Posted 07 July 2019 - 02:12 PM

Hi, just take a check-lamp and connect it to plus somewhere. ( I took C157-1 on the main-relay) connect to C159-2 on the ecm and switch on ignition. Lamp should light up.Then connect to C154-3 on the relay.pack .Turn on ignition, lamp should light up as well.So the wire from ecm to relay-pack is ok too.

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#5 mpialan

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Posted 07 July 2019 - 04:09 PM

Thanks for the reply. Unfortunately it will be next weekend before I can have a play.



#6 FlyingScot

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Posted 07 July 2019 - 05:27 PM

When you say it won’t start do you mean it turns over but fails to fire? Commonest cause of this is crank sensor.

Worth a quick check as “no crank” will stop fuelling.

FS

#7 mpialan

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Posted 07 July 2019 - 07:20 PM

I think my problems may be down to poor connections to the Relay Module. Wiggling and holding the connectors in place I can get the Module 'clicking'. I had no problems with the Aftermarket SC loom but, a brand new Rover loom may be at the root of my problems. Next weekend I am going to try and pull the connectors tight using cable ties. You can fix anything with cable ties and gaffer tape!







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