Why Does My Engine Misfire?
Discussion
People who know about points type ignitions needed.
I have an old VW Golf Driver which I am going to eventually get round to selling, but at the moment it comes in handy when it's p*ssing down with rain and I don't fancy dicing with death in my MR2.
It's pretty much always done it, but WHY does it misfire at high RPM when the engine's cold? The theory I've come up with is this:
Electricity from the battery goes to the primary coil winding and then follows a path to earth through the closed breaker points of the distributor thus creating a magnetic field around the secondary coil winding. When the breaker points are opened by the distributor cam then the current in the primary winding of the coil collapses, thus creating an electric current in the secondary winding, which then follows a path to the distributor cap, rotor and on to the spark plugs in each cylinder.
Assuming that I've got this correct (which I think I have but I'm not completely sure), could it be that when the engine is running at higher RPM the points are closed for a much shorter duration and therefore there is less time for a suffiecient megnetic field to build up around the secondary coil winding, meaning that not enough electricity is then distrubuted to the cold spark plugs?
I recently changed the 'plugs, dizzy cap and rotor arm on the Golf, but I'm thinking that maybe I need to use a different type of spark plug... Am I right?
>>> Edited by DanBoy on Saturday 7th February 20:27
I have an old VW Golf Driver which I am going to eventually get round to selling, but at the moment it comes in handy when it's p*ssing down with rain and I don't fancy dicing with death in my MR2.
It's pretty much always done it, but WHY does it misfire at high RPM when the engine's cold? The theory I've come up with is this:
Electricity from the battery goes to the primary coil winding and then follows a path to earth through the closed breaker points of the distributor thus creating a magnetic field around the secondary coil winding. When the breaker points are opened by the distributor cam then the current in the primary winding of the coil collapses, thus creating an electric current in the secondary winding, which then follows a path to the distributor cap, rotor and on to the spark plugs in each cylinder.
Assuming that I've got this correct (which I think I have but I'm not completely sure), could it be that when the engine is running at higher RPM the points are closed for a much shorter duration and therefore there is less time for a suffiecient megnetic field to build up around the secondary coil winding, meaning that not enough electricity is then distrubuted to the cold spark plugs?
I recently changed the 'plugs, dizzy cap and rotor arm on the Golf, but I'm thinking that maybe I need to use a different type of spark plug... Am I right?
>>> Edited by DanBoy on Saturday 7th February 20:27
To be honest danboy its probably none of that scientific mumbo jumbo stufff and a tesco carrier bag will solve it!! dont ask me i cant explain why but vw dizzy caps have a bad tendency to let moisture in when wet and i bet my life its cross fire your suffering in the dizzy cap, i know its a bodge and i am not really into them but the only way i cured mine was tesco carrier bag round the dizzy cap!!
the points can also go out of adjustment, and a change in fully open points gap will equate to a change in ignition timing (that's why you need to check the timing after changing the points)
Had similar symptoms once on a (wait for it) Lada 
which was caused by a hairline crack in the rotor arm. HT current was tracking down the crack (oo..er) when it was cold / damp. Friendly AA man tracked it down and cured it by painting over the crack with nail varnish 
...never did get an explanation why he was carrying nail varnish tho....
>> Edited by tigerk on Wednesday 11th February 13:15
which was caused by a hairline crack in the rotor arm. HT current was tracking down the crack (oo..er) when it was cold / damp. Friendly AA man tracked it down and cured it by painting over the crack with nail varnish ...never did get an explanation why he was carrying nail varnish tho....
>> Edited by tigerk on Wednesday 11th February 13:15
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