SOLVED: Ignition Warning Light - K Series

[JohnJo]

Hi all,

About 20 mins ago Spanky's red engine warning light came on. (Ignition Warning Light)

2002 140 SV 1.8 K Series X Power, unmodified. About 22,500 miles. Overdue a service by about 5 days.

I was pootling about for about 35 mins, grinning mostly, then accelerated hard for a couple of overtakes just before home. The light came on just after second acceleration.

Oil pressure as normal (mechanical stack), engine temperature as normal. Engine still responsive and sounding good.

Garaged it. Turned off and set imobiliser, then disabled imobiliser and restarted. Light still on. 

Any ideas appreciated. Last engine I took care of myself was a Spitfire 1500 so not up to speed...

Cheers

UPDATE: Handbook says "Ignition Warning Light" (not, as I put, "Engine Warning Light")

 

[Jonathan Kay]

Private Message sent.

Jonathan

[Wrightpayne]

Alternator and its wiring is what to look at. Any haynes manual should give you the general diagnostics.

[JohnJo]

Thanks for the reply. Jonathan has been kindly walking me through some stuff. So far all the wiring from the alternator to the battery seems solid. Belt good. Have ordered a multimeter and will take it from there.

[john milner]

Most likely either the alternator or the regulator. Once you have tested the voltages and it if looks like something in the alternator department is at fault it could be worth just buying a new regulator (£20-£30) and trying it as that has a higher chance of being at fault than the actual alternator (£50-£80). A recon alternator would normally include a regulator so if you ended up buying both it would mean an overspend so there is a small gamble either way.

https://www.mg-rover.org/threads/alternator-regulator.866545/

[JohnJo]

Hi John,

Thanks for the reply. Will see what the multimeter says later on today.

[JohnJo]

Update FWIW: Handbook shows the 7 went back to Caterham to have a starter button fitted very soon after original purchase. Not sure if relevant.

So this is what has been discovered using a multimeter with guidance from JK:

Reading at battery with engine off: 12.47
Reading at battery with engine running: 14.16 dropping to 13.9
Reading at battery with engine running at 3000 revs: 14.24 dropping to 14.17

Ignition Warning light remains on after ignition/engine running, which wasn't the case until a few days ago.

It's been suggested to me that the problem could be the connector behind the tacho. I've had a feel around and found nothing loose.

I may have to just live with this until I manage to get her to mechanic at end of June.

 

 

[TomB]

I'd suggest a failed diode pack on the back of the alternator.  The voltages look OK to me - the alternator would appear to be charging the battery.  

As I recall, in simple terms (the only ones I know ) the diode pack / regulator should trigger the red light if the charge of the alternator drops below the battery voltage when its running.  

Getting the alternator off isn't difficult (2 hanging bolt, 1 adjuster bolt, unplug connector).  Then you could find an auto electrician to test it, or see if you can borrow one locally to test.  

[mudguard]

... not forgetting the thick power lead which leads to the starter motor and then to the battery.  So disconnect the battery first!

Pretty much the same thing happened to me. I chose to simply replace the whole alternator with a reconditioned one. As it turned out I was glad I did as, aside from its (presumed) failed diode pack, the old alternator was just about ready for reconditioning itself!

The replacement wasn't expensive and came in the post from Schmitz Rotary Engineering. It has worked perfectly ever since.

[JohnJo]

This problem has now been solved with the kind help of Andrew (revilla) & Jonathan Kay. Andrew suspected a:

"faulty diode in the rectifier section of the alternator" which  "can leave some phases of the winding coming into play and some not; the result being pulsating voltage at the regulator with regular dropouts. So the battery will still charge (over most of the cycle, so not full strength) but the warning light may still be on (over the rest of the cycle, so maybe not full brightness but sometimes hard to tell). A multimeter wouldn't show that fault very clearly, the waveform is too fast. A scope probably would".

Amazingly Andrew offered to stop of at my place on the way elsewhere and replace the alternator with a unit he already had (we did keep our distance, which was relatively easy). I fired the Seven up and no warning light :)

Thanks again to them both and to everyone else for their comments and suggestions.

 

[revilla]

You're most welcome. Was nice to meet you. Glad we got it fixed. I'll see if I can see what's wrong with the old one.