Electrical problem - killing me!

[RichP]

hi.

What could cause all electrics to “trip” until I disconnect and reconnect the battery?

Bit of background:

I lost my dials, clock, and dimmer switch. It was fuse 31 blown. When I replaced it immidiatelt blew. I assumed it was the light switch as the dimmer rheostat was knackered. I removed this, and “fixed” it (removed the rheostat element and soldered a connection to keep it on). Re connected and everything works. Put the heater vent back in and it’s blown again.

Did this a couple of times, checked wiring as much as possible, no matter how much I move stuff I can’t blow it deliberately.

So for now I leave it dangling, but every so often, not every time, when I start the engine it does half a turn, makes a clonk, and everything is dead. Not even key operated central locking works. If I disconnect the batt and reconnect it all works fine again. And fuse 31 is not even blown.

Could the immobiliser cause complete power loss to everything? That shares fuse 31.

It’s not the light switch as I can have that connected and in use and everything works. Plus it no longer blows the fuse, just everything else.

I’ve run out of ideas!

Thanks

 

[Sean d]

My initial thought was something to do with the immobiliser, have you had it on a diagnostic reader.

 

[t-tony]

Does this happen only when you're trying to start the car?

Tony.

 

[RichP]

I thought the immobiliser still let the engine turn over but cut the spark..

The current issue is only when I start the car, but it’s instant, the starter motor clonks once (not click like a dead batt, but a kind of 1/4 turn) then everything dies.

I have just found this elsewhere...
http://zroadster.net/forum/viewtopic.php?t=38652#p361214
He reckons it was just a loose batt connection. I did remove the battery cable when I fixed th switch, and it wasn’t fully tight. But could this really cause a full cut out of everything? It was definitely still in contact, so could the ecu be shutting everything down because it had inconsistent power?

I have tightened it, and so far it’s working, but I can’t test it properly as I have ran the batt flat testing now. So need to charge back up.

 

[Redline]

A discharged battery can also cause lots of odd things to happen.
Could also be a combination of things - poor battery connection, drawing lots of amps, current across the poor connection can't be maintained, battery voltage collapses, and one of the control units says I'm out.

 

[RichP]

Ok thanks. I’ll give it a good run out tomorrow, see how it goes with tight connections and a full charge. Thanks. I was ready to set fire to the thing earlier!

On a side note, to save £140 for a new rheostat unit, my simple modification which puts the dash on full brightness seems to have done the trick!

 

[t-tony]

Been out tonight, my next question was going to be have you had the battery tested?

Tony.

 

[mrscalex]

I thought the immobiliser still let the engine turn over but cut the spark..

In effect but it doesn't cut the spark as such. The immobiliser (EWS) makes its security checks and if it's happy it has the responsibility for releasing power to the starter. If the engine turns over you know the EWS is happy with security checks. If it doesn't turn over you are either failing security checks, the EWS has become faulty (eg the internal starter relay has failed) or you have a fundamental failure like a flat battery

The EWS then passes the baton to the DME. Which will make its own checks and if happy it will enable ignition of the engine (the starter is turning while it thinks about this). Its last role in the startup sequence is to send a message back to the EWS when the engine has fired. The EWS then disables power to the starter. Which is why unlike older cars you can't turn the starter over with the engine running on a Z3.

So yes, the immobiliser/EWS is responsible for cranking but the DME makes the decisions on whether to enable ignition based on the baton being passed by the EWS.

 

[Althulas]

@RichP https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/232729304434 if you like a cheap spare.

 

[mrscalex]

@RichP https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/232729304434 if you like a cheap spare.

Careful. That’s not for a Z3 despite the heading. It’s for an E36 only. It has too few pins.

The Z3 part is 61318353506.

 

[Althulas]

Careful. That’s not for a Z3 despite the heading. It’s for an E36 only. It has too few pins.

The Z3 part is 61318353506.

Thank you saved me droping a clanger good spot though.

 

[RichP]

Update: since i got it working i haven't blown any more fuses or had any other troubles. So i appear to have fixed it by doing nothing. As i removed the gubbins from the rheostat i cant dim my dash - but its not worth £142 for the pleasure of that function.

Thanks for the info on the immobiliser system though. Despite it not being the problem i am always more than happy to learn about how Z stuff works for future reference!

 

[Bampz]

Hi
My brother had the same issue with his Focus , tried to start and just a dull click and dash lights went dead was a slightly loose battery connection but wouldn't tighten up property so new connection no more issues