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Misfiring Under Acceleration, And Flickering Ignition Light.


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#1 Chris1992

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Posted 18 August 2018 - 12:02 PM

Hi guys, so I was in London last night for a photoshoot at a bunch of different locations, when on the way back my car suddenly developed a slight misfire while accelerating. It seems to be intermittent though, as sometimes I could pull away from a standstill and bash it through all the gears up to 70, and then 5 seconds later while cruising at 70, if I try to put my foot down slightly to overtake a lorry, it'll cough and splutter horribly. 

 

The other symptom is that I've noticed that the ignition light is behaving strangely. At one point it didn't come on when I turned the ignition on, but then came on when the engine started, and then after 5 seconds flickered and went out. Other times while driving back I noticed it start glowing and flickering slightly and at times it would come on a few seconds, and the go out again. All very strange. 

 

Am I right in thinking this could be something to do with the alternator? Maybe a loose connection somewhere? If it was the alternator failing then would the ignition light not come on while driving and then stay on?

 

Any help would be much appreciated, I've got a large show tomorrow which I was hoping to take the car to, so I'm desperate to get it fixed!  

 

Thanks guys

Chris



#2 Chris1992

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Posted 18 August 2018 - 12:03 PM

Sorry just realised this should have been in the technical section



#3 WillCarter

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Posted 18 August 2018 - 01:26 PM

Have a look at this: http://www.theminifo...nd-it-misfires/

A couple of reasons are empty dashpot and dirty airfilter

Edited by WillCarter, 18 August 2018 - 01:27 PM.


#4 WillCarter

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Posted 18 August 2018 - 01:30 PM

http://www.theminifo...ignition-light/

The problem with the ignition light could be, as you said, the alternator packing in, which could then probably explain the misfire too. Check the battery's voltage to see if it has dropped

#5 Chris1992

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Posted 18 August 2018 - 05:27 PM

http://www.theminifo...ignition-light/

The problem with the ignition light could be, as you said, the alternator packing in, which could then probably explain the misfire too. Check the battery's voltage to see if it has dropped

 

 

I checked the batteries voltage and interestingly it still reads 12.6v dispite driving 2 hours back from London with my headlights and leccy fan on, although I also tested the alternator which shows a drop in voltage when the revs increase to 2k which obviously is not good, I don't understand how that's possible. I did also find a bad connection on the alternator which I fixed but it still misfires. I should also stress that it's not constant, as in one minute I can put my foot down in 4th and it will charge up a hill no problem, and then suddenly it can't handle going round a cyclist on flat road... This to me says it's electrical issue. The strange behavior with the ignition light is continuing too. It doesn't come at all when the ignition is switched on, but then will glow and flicker faintly while the engine is misfiring or under load.



#6 WillCarter

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Posted 18 August 2018 - 05:40 PM

It sounds to me like you've got a loose/faulty connection somewhere then.

Have you replaced the spark plugs to see if that helps at all?

It could possibly be that your mixture is too lean at high rpm too.

Edited by WillCarter, 18 August 2018 - 05:48 PM.


#7 Gillybobs

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Posted 18 August 2018 - 09:16 PM

Have you checked the earth strap from the engine to the body isn't loose or corroded ? Easy things first .

#8 Chris1992

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Posted 18 August 2018 - 09:36 PM

Have you checked the earth strap from the engine to the body isn't loose or corroded ? Easy things first .

 

Yep earth strap is all good 



#9 greenwheels

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Posted 19 August 2018 - 09:22 AM

Check the voltage across the battery with the engine running. This gives you the voltage produced by the alternator which be around 14.2-14.5 volts at a fast tickover. If it's not and all connections are good then replace it.



#10 Chris1992

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Posted 19 August 2018 - 08:54 PM

Check the voltage across the battery with the engine running. This gives you the voltage produced by the alternator which be around 14.2-14.5 volts at a fast tickover. If it's not and all connections are good then replace it.

 

Funnily enough I actually replaced my battery today. I was determined to get to a show so I packed a charged spare. Obviously it died on the way home so I swapped them over and carried on, didn't fix the misfire though :/ 



#11 greenwheels

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Posted 20 August 2018 - 07:17 AM

 

Check the voltage across the battery with the engine running. This gives you the voltage produced by the alternator which be around 14.2-14.5 volts at a fast tickover. If it's not and all connections are good then replace it.

 

Funnily enough I actually replaced my battery today. I was determined to get to a show so I packed a charged spare. Obviously it died on the way home so I swapped them over and carried on, didn't fix the misfire though :/ 

 

If the voltage is low measured as I described it's the alternator you need to replace. Assuming of course that the fan belt isn't slipping badly.



#12 Quincy Sparks

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Posted 21 August 2018 - 03:50 PM

 

Have you checked the earth strap from the engine to the body isn't loose or corroded ? Easy things first .

 

Yep earth strap is all good 

 

And the one on the battery? I had similar symptoms recently and discovered it was hanging on by just a few strands of wire!



#13 Chris1992

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Posted 21 August 2018 - 09:20 PM

And the one on the battery? I had similar symptoms recently and discovered it was hanging on by just a few strands of wire!

 


 

 

Yeah that one is perfect too! In fact I replaced it not too long ago due to it being the cause of a similar problem. 



#14 timmy850

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Posted 22 August 2018 - 03:41 AM

Do you have a tacho installed? Does the needle go crazy when the misfiring happens?

 

You mention the ignition light isn't coming on when the ignition switch is turned on (I assume with the engine off?). Can you check what terminal the warning lamp is connected to on the alternator? 

 

 

As above, check the voltage at idle. Without +14V you need to have a good look at the charging circuit



#15 harrythehat

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Posted 22 August 2018 - 07:32 AM

Taking a guess at the symptoms from previous experiences of life. (50 years or so of messing with motors and not being a techno)

the brushes in the alternator are getting worn out which is why the lights flickering

simples.






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