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metro
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Discussion Starter #1
Hi

Does anyone know if the 3AS and 5AS Lucas units are pin compatible?

Specifically can I plug a 3AS (and matched engine ECU) into a loom that previously had a 5AS (and matched engine ECU), and expect it to work?

Thanks!

Stuart
 

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rover_45
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The pins are the same. The 3AS does not have to be coded to the engine ECU as it completes the ignition circuit.

There is no way a 3AS will work with an ECU that works with a 5AS as even a new uncoded one is set into a default mode without the setup been done.

You either have some sort of other electrical issue thats stopping the car from starting or you have got the ECU's mixed up.

One thing is for certain a MEMS ECU that requires a 5AS code will not work with a 3AS alarm unit and will not work without a code unless you have a seprate box put in.

However an older MEMS ECU from a SPI Metro will work with your car and require no alarm unit at all, just aslong as your handy with the wires.
 

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metro
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Discussion Starter #3
That makes sense.

Can you explain why a 3AS (with its matching ECU), won't operate (or even flash the alarm light) when plugged into a loom that used to have a 5AS?

I have bypassed the immobiliser by bridging a certain wire to ground, so now the car turns over via the ignition key, but the injector still doesn't fire. I was wondering if some late 3AS / ECU combos actually had the "coded" treatment too.
 

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rover_45
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The 3AS is not coded to any ECU. That means you can change the alarm unit or engine ecu and not require it to be coded to each other.

The 5AS sends a signal to the MEMS ECU, if this coded signal is not the one the engine ECU was expecting it will do nothin. It wont even fire up the fuel pump in most cases.

The method I told you via PM should have sorted for a tempory measure. The only other thing I can suggest is PM me your reg number and I can have a look and see if yours has the additional immobliser realy. Which I very much doubt.
 

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metro
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Discussion Starter #5
Ok thanks. Maybe I do have some other issue. It just seems VERY strange that two days ago, I had the original 5AS and original engine ECU on the car, and it ran fine. Then I swap the 5AS for a 3AS and also the engine ECU from the 3AS car -- boom, doesn't work. So then I go back to my original setup, and the car won't de-immobilise, and won't work.

One other question, I take it the only immobilisation done by the immobiliser is the starter and not the fuel pump?, I actually hear the fuel pump whirr up when I turn the ignition on so I take it that's all good?

Thanks for the reg number offer, I'll PM you.

Stuart
 

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rover_45
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It is strange which is why I suggested you check all the fuses under the wheel and under the bonnet. As no damage should have happened to any of the ECU's.

But just double check them all and see what happens.
 

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Ok thanks. Maybe I do have some other issue. It just seems VERY strange that two days ago, I had the original 5AS and original engine ECU on the car, and it ran fine. Then I swap the 5AS for a 3AS and also the engine ECU from the 3AS car -- boom, doesn't work. So then I go back to my original setup, and the car won't de-immobilise, and won't work.

One other question, I take it the only immobilisation done by the immobiliser is the starter and not the fuel pump?, I actually hear the fuel pump whirr up when I turn the ignition on so I take it that's all good?

Thanks for the reg number offer, I'll PM you.

Stuart
3as ecu uses a different pattern flywheel aswell and are not compatable to 5as ecu.
You need to buy a R100 SPi ecu, 5as box and fob. Have you tried pressing the fob loads of timeson your originals rapidly as this usualy kicks my kit back into life after removal.
 

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Hi

Does anyone know if the 3AS and 5AS Lucas units are pin compatible?

Specifically can I plug a 3AS (and matched engine ECU) into a loom that previously had a 5AS (and matched engine ECU), and expect it to work?

Thanks!

Stuart
Hi, I appreciate this is an old post but I've literally just carried out this on my mini, I was wondering if you ever got to the bottom of it, what wiring changes do I need to make? Because it definitely didn't like the 3as alarm with the original 5as loom, thanks in advance, Luke.
 
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