Limp mode / severe hesitation / cutout

[Crumpet]

Well, for the first time in ten years of ownership my 500 has let me down. It’s managed to maintain its 100% record of never leaving me stranded on the road but it did finally cut out on the driveway - pretty lucky to make it home really.

Anyway, the symptoms:

It’s been running great up until yesterday but I’d forgotten to plug in the battery conditioner while I went away for three weeks and came back to a completely flat battery. Plugged it into the CTEK, tried again this morning and she fired up on the first crank. Great.

Drove it normally for twenty minutes or so but did notice it felt a bit lifeless. Then went to give it some beans and it felt rather flat above 4000rpm, almost hesitating. Then on a couple of occasions it got to 5000rpm and completely cut out - almost like the fuel was being cut.

Then I went out a few hours ago to see if it had mended itself and it had got much worse. Anything more than about 1/8th throttle causes it to miss and cut fuelling. It would drive with the barest amount of throttle but wouldn’t go above about 2300rpm.

Then as soon as I pulled onto the driveway it cut out and that was that. It no longer starts. The fuel pump primes but nothing happens when you turn the key. One thing I have noticed is that even with the ignition off the heater LEDs and the handbrake warning lamp are faintly illuminated and I can’t work out why!

To be honest I don’t have the time to tinker with cars these days, as much as I’d like to. I’ll have a few hours on it tomorrow but any suggestions?

I was thinking:

100amp fuse
Air intake hose collapsing
Knackered battery?
Distributor cap and rotor arm

None of those, other than the fuse, would stop it from even turning over though. Any help appreciated before it gets sent away.

[Steve_D]

Those symptoms are all making me think the battery was, and is again, flat.
You don't mention a charge light but that may look fine but in the background a charge is not getting to the battery. Possibly the 100amp fuse but many other causes could be the issue.

Get the battery fully charged and see if the problems go away.

Steve

[Crumpet]

Well, good shout on the battery! Took it back to Halfords as it’s only two months old and they confirmed it was dead. Fortunately they’ve replaced it under warranty.

Installed in the car and everything works exactly as it should, started on the first crank, picks up fine and drives as it always did.

So, either I completely ruined the battery or the battery isn’t actually getting charged. I checked the voltage across the posts before and after installing and it showed 12.8v. After starting it showed 12.5v and after a 20 minute drive it now shows 12.2v. Is that suggesting that it’s losing charge and not actually charging? Is there a better way to check whether it’s taking charge?

[Belle427]

You alternator isn't charging the battery, it should be closer to 14 volts.
Check the 100 amp fuse under the car.
You can check the charging voltage at the alternator large wire just to see if it's ok.

[Crumpet]

Belle427 said:

You alternator isn't charging the battery, it should be closer to 14 volts.
Check the 100 amp fuse under the car.
You can check the charging voltage at the alternator large wire just to see if it's ok.

Thanks! That’s what I thought, when I’ve checked on previous cars it’s always been running about 14v with the engine running. Better get the axle stands out....

[Steve_D]

Check at the alternator first before you go diving underneath,
If you have around 14ish volts then the 100amp fuse is the likely culprit.

When you check the fuse don't just look at it you need to remove it. The normal failure mode is it fracturing due to vibration so can be difficult to see.

Steve

[Crumpet]

Thanks chaps!

Come to think of it there was quite a racket coming from the engine bay a couple of weeks back. I thought it was the power steering pump being noisy but it could well have been the bearings on the alternator. The noise has stopped now and the steering is fine so I reckon it’s probably the cause.

I might be being a bit stupid here but where do I measure the voltage at the alternator? It’s not something I’ve ever needed to do before. Is it +ve to the alternator output and -ve to the chassis?

[Crumpet]

Ok, worked out how to measure it - used the output and the exhaust manifolds.....

Anyway, voltage across those points was 12.3v, same as the battery.

Alternator buggered then?

If so, which one are people replacing with these days and is it a tough job? Happy to spend a morning on it but don’t want to be spending days!

[Belle427]

Fairly easy to change although the bottom bolt is a little hard to access.
Is your charge warning light coming on as normal when you turn ignition on?

[Steve_D]

Belle427 said:

Fairly easy to change although the bottom bolt is a little hard to access.
Is your charge warning light coming on as normal when you turn ignition on?

Good question.
Some alternators need the charge light working to 'Stimulate' the charge circuit so if, for instance, the charge lamp bulb has failed the alt. may not start charging.

Steve

[Crumpet]

Belle427 said:

Fairly easy to change although the bottom bolt is a little hard to access.
Is your charge warning light coming on as normal when you turn ignition on?

Er.....I’m not sure but they’re doing g very strange things.....

With ignition off I have the oil lamp illuminated, like so:



With the ignition on I have the battery lamp illuminated, like so:



And with the engine running I have no warning lamps on. Doesn’t seem right at all and I’ve often wondered whether the two lights are connected the wrong way round anyway!

Edited by Crumpet on Tuesday 23 July 18:13

[JonathanT]

Someone else on here had similar weird lights. Both should be off with ignition off, then both on with ignition on, then both off again with engine running.
They found their lights were swapped over too, and they had a fault on their alternator (like yours sounds like it does).

[Belle427]

On the back of the alternator you will see a brown/yellow wire, its normally fixed with a 6mm nut. (small gauge wire)
if you touch this to the alternator body with ignition on it should light the charge warning lamp, this will prove if its connected to the right place.

[Crumpet]

In case anyone searches and finds this thread in the future I just thought I’d wrap it up....

It was the alternator. Twenty minute job to fit the new one and it now has 13.9v at the battery with the engine running. Looked like the original alternator so pretty good going really and four years SORNed probably didn’t do it any favours. Incidentally the new one is absolutely identical, even down to the Magnetti Marelli stamps - not bad for £120 given that some specialists are selling the originals for £900!