Topic

Yeah, I can't find a pin out for the ECU to identify whats connected on that plug to investigate further. Its either the ECU or something connected to that plug



The fuse blows straightaway unless the battery has been disconnected and then as soon as key is turned from position 1 to 2

Can you confirm the fuse wont blow in either of these distinct scenarios (e.g disconnect one or the other rather than both at the same time) :

Remove that specific relay only then turn on the ignition?

Disconnect the ECU connector only then turn on the ignition ?

If I remove the ECM relay in the boot with the ECU connected then the fuse does not blow.

If I have the relay in place but disconnect the small connector to the ECU, again the fuse does not blow.

***edit to add, I could hear the fuel pump when I had the covers off but can't hear it from inside the car, had son turn the key to P2 for me. Is that normal or should it be easily heard?

It depends on the individual car I think. In both of mine i can only just about hear the pump starting up from inside the car when there is no background noise.

OK so no nearer to the cause but have the car running again

The previous owner had fitted a battery isolator so something in my mind made me try using that to turn the power off, replace the fuse, put key and turn to position 2 then restore power. Fuse doesn't blow, usual immobiliser beeps, press unlock on fob to disarm and turn for ignition and the car starts instantly
¯\_(ツ)_/¯

Drives home flawlessly. I am developing a love/hate relationship with this car!

Argh its so annoying when the old advice of 'have you tried turning it off then on again' actually works but there's no evidence of why the fault occurred.

Im wondering if there could be a non obvious partially stripped wire in the loom that is occasionally touching a metal edge or perhaps another partially stripped adjacent wire. Now it is running again it could be worth grabbing the wiring loom around the ECM relay and the ECU connector and moving it about to see if anything happens.
Also knock and move the ECM relay in case this might have an intermittent internal short

In fact following that thought it would be worth shaking handfuls of the wiring loom wherever you can access it

Concentrate on the love part of the relationship, it makes the hate part easier to bear when you have problems.
I commented earlier about prior owners adding paraphernalia to their cars & then when we become the new custodian, we don’t understand why it’s there, how it works & what made them fit it in the first place. Then all sorts problems arise.
Unless you understand all the above rip it out & return it to original. If my car were to leave the family the new owner would be comprehensively flummoxed. Fortunately all my mods are cataloged & as my daughter in law will inherit it’ll be in very safe hands.
M

I would not bother with that small connector of the engine ECU. That connector carries only ground wire of ECM relay coil. That means if you disconnect it you disable the possibilty for it to energize the relay coil when ignition key is turned to position 2.


You have a problem when relay is energized and provides power on its "exit" terminal which has some connection to ground.

At times when your fuse start blowing you can check this and measure connectivity with multimeter from relay's base "exit" terminal to ground. I expect that you will have firm connection to ground.

Since exit terminal has Brown/Pink wire attached that wire is grounded somewhere on its path.

That wire provides power side for all engine important parts like injectors, purge control valves, solenoids etc...
Since that wire is grounded it does not provide any damage to mentioned engine units. However it does blow your fuse and render your car useless.

It would be useful to confirm this continuity to ground when this happen next time, and if so you need to trace where Brown/Pink wire goes or passes and see if there might be some brake in the wire touching metal or other bare ground wire.

Futher regarding your boot hinge wire break, please take a look the explanation at the end of thismthread where I explained what could happen with break in these wires: https://www.the-t-bar.com/forum/roverlike-s-guides/97856-mg-f-tf-boot-hinge-lid-wiring-loom-inspection-guide

Hi, there is a topic on here that may help ( I can't copy the link over for some reason)
It's called The Case Of A Blowing 30amp Fuse!!
Posted by Uncletone 9 years 5 months ago.

I am going to see if there is a local auto electrician that can possobly read the ecu for any stored codes. I have in the intervening period where the car has been running fine had the boot loom checked and repaired so there are no breaks there that could be causing this.

The 30 amp blowing article is here: https://www.the-t-bar.com/forum/9-mgf-tf-pitstop/91008-the-case-of-a-blowing-30amp-fuse The symptoms sound like yours..

A physical fault rather than an internal ECU fault does look more likely. Definitely do not send the ECU away until you have very thoroughly checked the wiring the article describes.

Managed to get the codes read and there was a stored code of P0135, specifying the heater circuit of the pre-cat lambda sensor. Live data showed it static at 0.475v

After watching this on YT the part from 15 mins suggest the sensor is caput, checked the wiring and there is no damage to short on the exhaust manifold.

Replacement ordered and will be a job for this evening/Sunday and hopefully this will resolve the intermitent issues.