Engine won't stop

[Matthew Willoughby]

As a bit of a change from the usual "my engine won't start" threads, I am regularly suffering from the opposite problem. When I come to switch the engine off, which I generally do via the battery master switch, sometimes the engine switches off immediately, other times it stops reluctantly and often it merrily keeps running, even with the master switch and ignition keys switched off and removed.

 

The onset of the problem seems to have coincided with fitting a new alternator after the old one failed. Could this be the cause in some way?

[Jonathan Kay]

1. Check if disconnecting the fan stops it immediately. 
2. Have you got a diagram for how the master switch is connected?
3. What sort of alternator and was it like for like or did you have to change connections or other wiring in any way?
4. Does it otherwise charge normally and does the ignition warning light come on with the ignition and go off as soon as the engine starts? Is the lamp an LED or a traditional incandescant?

Previous discussion.

Jonathan

[Drumster]

Hi Matthew,

I had a similar problem here, eventually convincing myself that a bad connection on the alternator caused it, although failing to understand the reasoning behind it. Not had any problems since.

[SM25T]

Don't think using the master switch is a recommended way to stop the engine.

[Matthew Willoughby]

Thanks for all of the comments.

JK, in answer to your questions:

1 - it isn't linked to the fan as it does it  irrespective of being hot or cold

2 - I'm afraid not but the wiring hasn't changed which suggests this isn't the cause.  I have fitted a new master switch to rule our a MS fault.

3 - the alternator was the one that Redline stock for X flows and 8v Vauxhalls.  It wasn't exactly the same but the connections were similar.  Could switching the wires around on the alternator cause this problem?

4 - the alternator charges just fine but it does make a nasty whining noise so I'm going to send it back to Redline.  I don't think the whine is related to the running on issue.  The ignition warning light isn't connected for some reason, and never has been during my ownership, so I have no reason to think this is linked to the problem.

 

Chris, your problem seems very similar to mine.  It feels as though the car is continuing to run on the alternator as the engine revs drop momentarily when switching lights on and when I stall the engine to turn off I immediately lose all other electrics.  I need to have a closer look at all the alternator wiring.

 

SM25T - many racers use the master switch to turn off.  I understand that as long as it is a properly wired FIA switch this will not cause any problems.  I tend to do it this was as scrutineers will always check that the master switch stops the car and I want to know ASAP if I have a problem as I don't want to fail scrutineering.

[Jonathan Kay]

Could switching the wires around on the alternator cause this problem?

I need to have a closer look at all the alternator wiring.

"Yes", and that's where I'd start.

If you can find a part number for the alternator or similar or post a photograph of the terminal pattern and trace all of the current connections that should help.

The disconnection of the ignition warning light is intriguing. And that's come up before. I'd want that working properly at the end of this job.

I don't know enough about master switches or the ways they are wired, anyone... ?

Jonathan

[Bricol]

I'd be looking at the resistor and how it's linked, or not, to the master switch wiring.

 

[Paul Deslandes]

Does it stop normally if you only use the ignition switch, leaving the FIA switch on?  If so it would suggest a problem around the FIA switch and resistor.  I suspect that this is not the case but wanted to be clear.

Paul

[Matthew Willoughby]

I think Bricol's got it.

I had another play this morning and had the same problem initially.  Having turned off the master switch the engine kept running, even when I then turned the ignition switch off.  I turned the master switch back on and then the ignition key worked when used to switch off.

I then had a bit of a play with the alternator wiring but everything seemed to be alright.  On all subsequent tests the car switched off immediately on the master switch.  I noticed that the alternator whine mentioned in post #5 had stopped and decided to check the battery voltage to make sure it was still working.  I seem to have killed the new alternator.

What I think has happened is that the master switch resistor has failed which led to the failure of the original, old, alternator.  Having fitted the new alternator I checked that I was getting an output, which I was.  Having stopped the car on the master switch a couple of times the new alternator started to whine.  Later in the weekend the car exhibited the running on issue for the first time.  Thinking it was a switch issue I changed the master switch, but not the resistor.  The problem seemed to go away but soon returned.

Now the new alternator has failed the master switch is working just fine.  All of this, to my mind, points to the resistor.  I've just got to work out where it is so I can change it for the one that came with the new master switch.

[Paul Deslandes]

You should be able to get the alternator repaired at significantly less cost than a new  one as it will almost certainly be one of the diode packs that have failed.  A local automotive electrician should be able to do it for you.

The resistor should be located close to the FIA switch and is usually beige, square section and about 2 inches long with a wire coming out of each end.  Maybe one wire has either broken or become disconnected rather then the resistor failed.

Irrespective of whether racers shut off their engines with the FIA switch, it's a really bad idea, as you're finding out!!!

Paul

[TomB]

The resistor gets very very hot when you turn the engine off with the cut off key. Be careful. For this reason, I'd don't use it regularly to kill things.