Can a bad alternator cause loss of engine power & misfire?

[DevonMark]

As above.

Broke down on Saturday after, for the first time since last October, I had the 'mystery' problem again - van started losing power and 'chugging' before I pulled it in. Once engine was turned off it would not come back on again, had to be towed.

The van's been up with South West Splitz and they can't fault it (compression test fine). They have replaced alternator and think that that could be the problem.

Would a bad alternator cause that sort of break down?

It was a cold night and I had wipers on, lights on and radio on, so would a faulty alternator (and no charge) lead to loss of engine power?

Confused.

[AdrianC]

Did the charge light come on?
Does it normally come on when you turn the ignition on but before you start the engine?

If the answer's that the light was behaving correctly, then you had some charge. Possibly not keeping up with demand, but some - and unless your battery's very borderline or it was a massively long drive, that's unlikely to be the issue.

If the battery was getting to be very, very flat, then - yes - it'll start to run badly. Which engine? If it's a petrol injected, then you're going to have problems sooner than on a low-tech wheezel.

[DevonMark]

Yes, the battery was very, very low, to the point where once I'd pulled in and turn the engine off, it was completely dead (no charge for it to turnover).

So the loss of power could be down to having such a low charge? That's a relief. I have an underlying worry that it's an engine problem and hate things being undiagnosed!

It's a 1.9l petrol (1989), not injection.

[AdrianC]

Yes, the battery was very, very low, to the point where once I'd pulled in and turn the engine off, it was completely dead (no charge for it to turnover).

But lights hadn't started to dim?

What was the charge light doing? If ever that comes on, stop immediately and investigate - if the belt's broken or come off, you don't have a water pump either...

[Ralf85]

[quote="DevonMark"]As above.

Broke down on Saturday after, for the first time since last October, I had the 'mystery' problem again - van started losing power and 'chugging' before I pulled it in. Once engine was turned off it would not come back on again, had to be towed.

The van's been up with South West Splitz and they can't fault it (compression test fine). They have replaced alternator and think that that could be the problem.

Would a bad alternator cause that sort of break down?

It was a cold night and I had wipers on, lights on and radio on, so would a faulty alternator (and no charge) lead to loss of engine power?

Confused. [/quote

The alternator charges the battery and that fires the spark in your spark plugs. If the alternator brushes are worn out it won't charge, the battery runs out of juice and the sparkplugs cease to function. If your battery is not charging and you are using wipers, lights and radio, that will speed up the drain of juice. The brushes are part of the regulator which can also fail. A replacement regulator/brush pack costs a few quid thus saving the need to replace the alternator. Let's hope that your problem is now solved. Good luck.

[DevonMark]

Yes, the battery was very, very low, to the point where once I'd pulled in and turn the engine off, it was completely dead (no charge for it to turnover).

But lights hadn't started to dim?

What was the charge light doing? If ever that comes on, stop immediately and investigate - if the belt's broken or come off, you don't have a water pump either...

Lights probably did start to dim, but they're not the brightest anyway and was on a road with street lights so not easy to tell.

I honestly can't remember whether the charge light came on initially (when it first started losing engine power), but I don't think so. It may well have come on once it got really bad though and I needed to pull in.

[DevonMark]

The alternator charges the battery and that fires the spark in your spark plugs. If the alternator brushes are worn out it won't charge, the battery runs out of juice and the sparkplugs cease to function. If your battery is not charging and you are using wipers, lights and radio, that will speed up the drain of juice. The brushes are part of the regulator which can also fail. A replacement regulator/brush pack costs a few quid thus saving the need to replace the alternator. Let's hope that your problem is now solved. Good luck.

That is a hugely helpful explanation - thanks so much Ralf!

[California Dreamin]

Ralph pretty much nailed it....as the battery discharges it's voltage decreases. As the coil depends on a healthy voltage to create an adequate spark, the decrease in voltage to the coil reaches a point where the output of the coil isn't good enough to properly ignite the fuel and air mix in the combustion chambers...it then starts to misfire. This just gets worse until finally breaking down.

Martin

[DevonMark]

Ralph pretty much nailed it....as the battery discharges it's voltage decreases. As the coil depends on a healthy voltage to create an adequate spark, the decrease in voltage to the coil reaches a point where the output of the coil isn't good enough to properly ignite the fuel and air mix in the combustion chambers...it then starts to misfire. This just gets worse until finally breaking down.

Martin

Great, thanks.

This did happen before though, back in the autumn, and by the time the van had been towed to the garage it had miraculously cured itself, started and would not fault. Can this happen if the alternator is the problem? I would have thought that if the battery was dead enough to cause a break down for the reasons described above, that would be it.

Weird.

I guess it could have been that the first time it broke down it was because it needed a good service and new spark plugs etc sorted the problem out and it's just a coincidence that the failing alternator has caused similar symptoms this time, but I'm still concerned that its a more sinister engine related problem.

But if the compression test was fine, engine should be OK shouldn't it?

[AdrianC]

I guess it could have been that the first time it broke down it was because it needed a good service and new spark plugs etc sorted the problem out and it's just a coincidence that the failing alternator has caused similar symptoms this time, but I'm still concerned that its a more sinister engine related problem.

The fact that the charge warning light didn't come on makes me sceptical about the nice easy "lack of charge" diagnosis, though. I've nursed cars, not charging, back and had the real fun'n'games of trying to avoid braking because the brake lights mean there's not enough sparks left to keep the engine running. Or misfiring in time to the indicators... But it's taken a LONG while after the charge light's come on for it to get to that stage.

Forgive me here, Mark, but I'm assuming you're not the kind of driver who'll fail to notice/respond to a bright red light for tens of miles...?

[ghost123uk]

The van's been up with South West Splitz.... They have replaced alternator...

I bet the clue is there
Summat to do with a little blue wire (on the back of the alternator, it triggers the charging led by the way Mark, if it's not connected the charge warning led won't come on, ever).

[DevonMark]

I guess it could have been that the first time it broke down it was because it needed a good service and new spark plugs etc sorted the problem out and it's just a coincidence that the failing alternator has caused similar symptoms this time, but I'm still concerned that its a more sinister engine related problem.

The fact that the charge warning light didn't come on makes me sceptical about the nice easy "lack of charge" diagnosis, though. I've nursed cars, not charging, back and had the real fun'n'games of trying to avoid braking because the brake lights mean there's not enough sparks left to keep the engine running. Or misfiring in time to the indicators... But it's taken a LONG while after the charge light's come on for it to get to that stage.

Forgive me here, Mark, but I'm assuming you're not the kind of driver who'll fail to notice/respond to a bright red light for tens of miles...?

I would have noticed it if it had been on for miles, just might have missed it if it came on just as I was steering to safety through serious loss of power! Slight moment of panic

How far in advance of a full breakdown would you expect the charge warning light to come on for the 'lack of charge' diagnosis to be feasible?

[DevonMark]

The van's been up with South West Splitz.... They have replaced alternator...

I bet the clue is there
Summat to do with a little blue wire (on the back of the alternator, it triggers the charging led by the way Mark, if it's not connected the charge warning led won't come on, ever).

I'm too clueless when it comes to mechanics to decipher your post (I am trying to learn though!)

Do you think the alternator is the problem?


Ah sorry, I geddit now - so you're saying that the charge warning light may not have come on because the wire that powers the LED wasn't working?! The plot thickens! Can I test this by turning the van on and seeing if the charge light comes on for a few seconds?

[AdrianC]

I guess it could have been that the first time it broke down it was because it needed a good service and new spark plugs etc sorted the problem out and it's just a coincidence that the failing alternator has caused similar symptoms this time, but I'm still concerned that its a more sinister engine related problem.

The fact that the charge warning light didn't come on makes me sceptical about the nice easy "lack of charge" diagnosis, though. I've nursed cars, not charging, back and had the real fun'n'games of trying to avoid braking because the brake lights mean there's not enough sparks left to keep the engine running. Or misfiring in time to the indicators... But it's taken a LONG while after the charge light's come on for it to get to that stage.

Forgive me here, Mark, but I'm assuming you're not the kind of driver who'll fail to notice/respond to a bright red light for tens of miles...?

I would have noticed it if it had been on for miles, just might have missed it if it came on just as I was steering to safety through serious loss of power!

How fair in advance of a full breakdown would you expect the charge warning light to come on for the 'lack of charge' diagnosis to be feasible?

If we're talking about an alternator/wiring fault causing lack of charge only, then assuming a decent battery, and not sitting in urban traffic, then - even with lights/wipers etc - at least ten-twenty miles, possibly more. Less, if you've got a stonkingly large stereo and amp on or umpteen big fat driving lights.

If it's the belt that's gone, then not very long at all - but it'd be a cooked engine that stops you, rather than lack of charge. The temp gauge wouldn't warn you, either, since water won't be being circulated from hot bits of engine to the gauge's sender.

[DevonMark]

If we're talking about an alternator/wiring fault causing lack of charge only, then assuming a decent battery, and not sitting in urban traffic, then - even with lights/wipers etc - at least ten-twenty miles, possibly more. Less, if you've got a stonkingly large stereo and amp on or umpteen big fat driving lights.

If it's the belt that's gone, then not very long at all - but it'd be a cooked engine that stops you, rather than lack of charge. The temp gauge wouldn't warn you, either, since water won't be being circulated from hot bits of engine to the gauge's sender.

That makes sense. If it was the belt, surely the guys at SW Splitz would have noticed this? Perhaps I'll double check that they've checked it

Temp gauge was definitely not high when the break down happened.