15 replies to this topic

[andrewdjackson]

The white ignition wire burnt out in my SPi (1994 with single socket ECU) - interestingly, the fuse (1-2 35A) didn't blow.

I have done the following:

• Completely paired back the wiring loom
• Replaced the ignition barrel and switch
• Replace the white wire and the ignition barrel plug/socket
• Checked all other wires for integrity
• Tested the relay pack in a earlier SPi that was carb converted (with 2 socket ECU)
• Tested my ECU in the earlier SPi (worked ok - but does that prove anything?)
• I put the ECU on the bench all looks good - no burns etc.
• Tested that applying 12v to pin 11 grounds pin 4 - worked ok.

Now I'm not sure if the ECU test was valid - also I discovered I have a Lucas 3AS alarm/immob. fitted - but I've never had a fob or a light on the dash so assume it's been disabled.
How can I check / disable this?

The hazard lights and headlights/tail lights work - dim/dip works - but indicators and wipers don't.

Please any help would be appreciated.

Edited by andrewdjackson, 10 October 2011 - 02:09 PM.

[andrewdjackson]

As a follow on, those reading the other similar post:
1. when you turn the ignition on (position 2) do you hear the fuel pump prime? NO
2. When you turn the ignition back off again, do you hear the stepper motor 'click' as it resets? NO
3. Does the starter solenoid click when you switch the key over to position 3? NO
4. Does the immobiliser appear to be working normally - ie does the light go out completely when you disarm, also can you arm it as normal too ? (light flashing for a few seconds then blinking, you know the sequence) DON'T KNOW, NEVER HAD A FOB OR AN LED

The Diode on the Alternator had blown, I'm getting this fixed - would / could this cause this problem? Surely the care would start even if the alternator was not working?

[LukeMoss]

Does sound like an immobilser problem but seen as it's been removed, have you checked the inline fuses? And have you checked there is a feed getting to the fuel pump?

[andrewdjackson]

I've checked every fuse I can find even the fusible links - all are good - in fact strangely none of the fuses blew despite the wire getting fried.
I pulled the loom apart I checked all the wires I can get to - which leads me to think it's something component wise.
I've checked the relays on another mini - which leaves the immobiliser or the ECU.
Since I've never had an immobiliser fob or in fact knew I had one until now - I'm not sure how I diagnose this; the wiring is not well documented (no surprise).
ECU wise I'm hoping to try a donor ECU.
I had the alternator checked as I don't get an ignition warning light.
I can't fathom why I don't get an ignition warning light??
Surely this would work with or without the ECU?
Is the alternator circuit dependant on this buld not being blow?
One step forward and another 10 questions arise.

Edited by andrewdjackson, 10 October 2011 - 05:04 PM.

[xrocketengineer]

If I follow correctly what you have done so far, it seems that the main relay on the Relay Module is not working. When I tested my ECU problems I inserted a pin/needle in between the wire insulation and the weather seal of the wire I wanted to test on the back of the Relay Module connectors. In your case you need to check any wire that is brown with a pink tracer looking for 12V with the ignition on. If there is no voltage the main relay is not active. Also check for a ground/earth path on the wire that is white with a pink tracer that provides the earth path for the main relay and for 12V on the white wire with the ignition on (as you previously tested on pins 11 and 4 of the ECU).
Since you are not getting the ignition warning light to come on, I would bet that you are not going to get 12V on the white wire either. If that is the case, no power is coming out of the ignition switch.

Hope that helps,
Ivan

[Sprocket]

From memory the white ignition live is actually fed from the body loom through the ignition switch. I'd start by checking there is 12v on the brown wire on the ignition switch. Zero volts on this brown wire would indicate that one of the body loom fuse link has likely blown.

[andrewdjackson]

The brown wire has 12V on the ignition switch, I have manually activated the relays in the relay pack and have successfully managed to get the starter motor, fuel pump etc to run. 12V at pos II (AUX) then 0V at pos III (IGN) - although if I disconnect the Immobiliser and the ECU I get 12V - this maybe expected behaviour if the either the Immobiliser or the ECU are not playing the game.

I am, with various wiring diagrams and no.1 eyeball, gradually creating a definitive wiring diagram in Visio. One thing I've noticed is that when you start piecing together all the diagrams the white ignition wire splits, one changes to light green through fuse 1-2 off to the dim/dip relay. The other goes to the ECU and the Immobiliser.
The Crank (pos III) on the ignition switch runs a white/red wire to the Immobiliser and then from that a white/pink - white/red wire goes to the starter relay - interested in where this goes next and if I can bypass the immobiliser by linking WR wire to the WK wire? Thoughts?

[xrocketengineer]

Sorry, I got lost. When you say "12V at pos II (AUX) then 0V at pos III (IGN)..." on which wire are measuring that? Because, if I am not mistaken, in order to operate the relay pack (except for the starter), all you need is power on the white wire. Looking at the wiring diagrams, the alarm has outputs only for the starter (wk), the horn (pb) and the indicator lights (gr and gw). Unless I am missing something, I don't see anything on the alarm outputs that would prevent the ECU from activating the relay pack, other than no voltage on the white wire. My car has no alarm so some of this is new to me, so I am trying to learn.
On the other hand, if you have a "coded" engine ECU all bets are off. There has to be a different wiring diagram showing an output from the alarm to the ECU for the code.

[andrewdjackson]

You need the Rover circuit diagram, all the others (another 3 I have now!) don't show the immobiliser in the circuit.
The white wire has 12V, which splits in the loom into 3 places in parallel;

1. The ignition warning light on to the alternator
2. The ECU (MNE1010.. uncoded version)
3. The immobiliser (LA3)

I haven't managed to work out what colour the white wire emerges from the immobiliser but I expect it either does a colour change in the loom like the white/red does (see below) back to white and then to the ECU or it grounds it in the immobiliser to prevent the ECU activating the main relay. Here I think is the crux; either the ECU isn't very well and doesn't ground the main relay to start everything off, or the immobiliser is playing up and is interfering with the energising of this circuit. Don't really know at this point - how do I know if the ECU is sick? or if the previously inactive immobiliser is now active or sick?

The white/red wire (CRANK on the ignition) goes to the immobiliser emerges as white/pink then changes back to white/red up to the starter relay in the relay pack. If I bypass this and activate the relay directly the starter motor will run.

Interesting that you say that the horn (PB) and indicators (GR and GW) are via the immobiliser - because the indicators don't work except as hazard - although the horn is fine.

Edited by andrewdjackson, 12 October 2011 - 12:52 PM.

[xrocketengineer]

Well, I am using the Rover diagrams and all I found there that the alarm controls is the starter. Based on that, in theory you could bump start the car. So something must be missing or hidden in the diagrams. I looked at the MPI diagrams for reference and they show a connection back from the alarm to the ECU for the code.
I tell you, the Space Shuttle was simpler than this! LOL
However, if the indicators are not working, it points back to the ignition switch. No power is coming out of it on the white wire in pos II. No ECU or alarm involved in that. Either that or a broken wire somewhere.

Cheers,
Ivan

[Sprocket]

This lot might seem a little broken up and maybe a little repetative, but its stuff i'm noting down as its whirring round my head.

There has been no mention in this topic as to why the white wire burnt out in the first instance. That is where you should start to look!! the wire will burn out only with a dead short to ground or extreme overload. I'd be trying to find that than looking at anything else.

It's not clear which part of the white wire in the loom has burnt out, if you tell us this, it might make it clearer where the problem may lie.

The 3AS alarm imobiliser box inhibits only the starter motor. The 5AS box inhibits the starter motor as well as the ignition, injector and fuel pump circuits via the ECU digital code on the grey/ white wire. No matter what you do, you will never be able to wire round it 100% to even bump start the engine.

The white wire onto the alarm ECU is only for an input signal (ignition sense), much the same as it is on the engine ECU, there is no real load drawn on these circuits. The white also feeds the fuel pump relay coil in the relay pack, not the fuel pump itself, so again draws no real load. The white also feeds the charge warning light on the dash, again drawing no real load.

The brown from the fuse link onto the ignition switch in position II leaves as white to the fuse where it then is distributed to the above circuits. The wire from the ignition switch before the fuse is a very heavy wire since it needs to survive a dead short to ground long enough to make sure the fuse link blows instead of starting a fire.

The charge light on the dash works in a wonderful way. The white wire feeds 12v through the bulb onto the brown/ yellow wire to the alternator where it grounds. The current drawn by the charge light creates a magnetic field in the field winding of the alternator. This is what really makes the alternator work when it starts turning. Without it (bulb blown or missing) the alternator will not generate any voltage. OK so the alternator is generating voltage as the engine starts and as a result the charge light ground now has a 12v potential. one cancels out the other, the charge light draws no current. There is a hidden diode in the brown yellow wire that prevents the alternator back feeding 12v through the charge light, thereby keeping the ECU live and engine running even with the ignition key turned off and even removed from the switch altogether.

Ok so thats all explained, it should be easy to find where the fault is. If the wire that burnt out was the heavy white wire from the ignition switch and not the lighter gauge wires after the fuse, there is a ground fault on that wire somewhere, and likely blown the fuse link and likely damaged the ignition switch since 12v divided by 0.001 ohms would be 12000amps instantanious (can you see why the wires melt and burn?) Check for dodgy aditional wiring for the likes of a sterio or cigarret lighter/ socket.

With the burnt wiring replaced and the fault repaired, there should be 12v on the brown wires on the ignition switch and 12v on the white when switched to position II (IGN) or III (Crank). No volts on the browns means a fuse link has blown at the starter motor. 12v on the browns and no volts on the white at pos II or III means the ignition switch is faulty. Oh and there is the multi plug connector on the column, thats a good place for a bad contact as well

Going back to what you described earlier, if there is zero volts with both alarm and engine ECU's connected, removing them, there is 12v on the white, could suggest that perhaps there is a high resistance in the circuit, that drops the volts right off when any current is drawn (likely the ignition switch after the stress of 12000amps dead short in my mind)

Position I (Aux) will only have 12v on the green, the white will be zero volts.

You could disconnect the battery and check the resistance between the brown and white wires on the ignition switch with the switch in the correct position II or III. There should be zero resistance.

There couldn be a faulty engine or alarm ECU, alternator, or wiring, but you need to try and find why the wiring melted in the first instance and where it melted in the loom

Edited by Sprocket, 12 October 2011 - 10:36 PM.
missed out a teeny bit :)

[andrewdjackson]

Great post Sprocket - I'll check those points.
The white burn out was my fault - I accidently trapped it between the air filter housing and the injector feed pipe - difficult to spot, but I'll be definately make sure that they are out of the way next time!!
The loom connector between the ignition switch barrel and the engine harness had melted, pretty much from the ignition switch right up to where the white wire splits it had melted the sheathing on the (heavy) white wire (thin whites were ok). I unpicked all of the loom taping, checked all the wires alongside the burnt wire and then replaced the white wire, I also replaced the ignition switch barrel with a new one and replaced the loom connector.
The Rover MEMs manual states that 12V on pin 11 will cause the ECU to ground pin 4 - this runs up to the main relay in the relay pack - if this does not activate then fuel pump and starter relay will be unable to activate?
Either way reading your post, if I was to disconnect the alarm I think I should get the main and fuel pump relays to activate if 12V is on the white wire in pos II?
If I don't get 12V on the white wire with the alarm disconnected do you think I'm looking at an ECU fault if there is zero resistance between the white wire at ignition to the ECU?
Thanks for your help.

[Sprocket]

Without the alarm box if it is a 5AS, you will not get the fuel pump, ignition or injectors to work as the ECU needs the digital code the alarm box sends out. The 3AS alarm box only disables the starter relay.

Removing either alarm or engine ECU results in 12v seen on the white wire, but disapears when they are refitted would suggest a few scenarios.

1. The alarm ECU is faulty pulling the 12v to ground (fuse should blow)
2. The engine ECU is is faulty pulling the 12v to ground (fuse should blow)
3. a combination of 1 and 2 (fuse should still blow)
4. there is a high resistance in the white wire between both ECU's and the ignition switch.

Point 4 I will explain. With a circuit that has 12v and a high resistance, and is not grounded, there will be 12v either side of the resistance. The resistance can very high and you will still get 12v after the resistance. If you ground the circuit, (The alarm and engine ECU's in this case), the high resistance reduces the voltage right down to zero in some cases.


If this is sounding similar to what you are experiencing, you need to find this resistance. If you get zero volts on the white with the switch in the correct position and both ecu's still connected, check you are still getting 12v on the browns on the switch in the same position, no volts would suggest the fuse link, or the wire itself. If you still get volts on the brons, then the switch is faulty.

[xrocketengineer]

The scenario of Sprocket's point number 4 make's a lot of sense. If you measure the voltage on a 12V battery you get 12V. If you connect a resistor to one of the terminals and measure the voltage, it is still 12V. If you keep adding resistors to that terminal in series it will still measure 12V. However, when you connect a 12V light bulb to the resistors and to the other terminal of the battery it will not light up or be very dim. When you measure the voltage at the light bulb terminals you will find out that the voltage is much less that 12V.
This type scenario occurs even with car batteries. You measure the voltage at the terminals and is 12V. You turn on the dome light in the car and the voltage drops to near zero because the battery is damaged and has developed high internal resistance.

[andrewdjackson]

xrocketengineer and Sprocket many thanks, with your help. I managed to fix it.
Tracing the wires by isolating and measuring resistance and voltages I managed to find one of the fusible link wires was burnt out - once repaired everything worked again.

For the benefit of anyone else who may run into this problem here is what made this diagnosis tricky:
I had a few false positives in a number of ways which took me a while to find, namely:

The diagram shows fusible links between the alternator and the start motor, in fact the main 12V from the battery goes to the starter motor and splits off to the loom from there. There are actually 3 fusible link wires that go to various parts of the loom.

Measuring from the starter motor to other parts of the loom gave good continuity results even though one of the links had gone.

POS I on the ignition switch delivered 12V ok, POS II everything dropped to 0V as if there was a short circuit.

Isolating the white wire and adding a component at a time eventually delivered 10V at various points instead of 12V until the ECU was added when it dropped to 0.5V. This made me wonder why I only got 10V, so I isolated the wire again and traced from the battery working up into the loom measuring resistance and voltage as I went.

The faulty link gave a fluctuating reading between 9V and 11V - this is where I finally found the fault.

Now.. how do I fix the link? I have put similar gauge wire in for the moment - but haven't been successful in finding fusible link wire.