Heat related misfire

[Wilf]

Been out and about today around the new forest and south coast. Car on the whole behaved well, but if I get caught in a queue for long enough I pick up a misfire. Let the car cool a bit and it's fine again. Something obviously does not cope well with the heat. (Car never gets over ~95 on the guage for what that's worth). Misfire feels like a single cylinder drops as it's a very regular misfire, so I am ruling out the coil and lumenition for the moment. Will change plugs, leads cap and rotor arm for known good ones and see what happens, but as a general sanity check what else should I look for?

I did notice is that the lumenition wires from the distributer are incredibly "limp" for want of a better word, seem far too flexible - are they all like this?

[stevem]

If it was generally spluttering and missing I would maybe consider the fuel pump might not like being hot, I had that once on two previous cars that I owned. They ran great on a cool day or when moving along, but stuck in traffic jams or on a hot day would start playing up.

[Stink]

Been out and about today around the new forest and south coast. Car on the whole behaved well, but if I get caught in a queue for long enough I pick up a misfire. Let the car cool a bit and it's fine again. Something obviously does not cope well with the heat. (Car never gets over ~95 on the guage for what that's worth). Misfire feels like a single cylinder drops as it's a very regular misfire, so I am ruling out the coil and lumenition for the moment. Will change plugs, leads cap and rotor arm for known good ones and see what happens, but as a general sanity check what else should I look for?

I did notice is that the lumenition wires from the distributer are incredibly "limp" for want of a better word, seem far too flexible - are they all like this?

Hi i have the same problem ,really hot days the engine seams to have an iregular paterened missfire , after using the car on a hot day i noticed that when i went to close the driver side window it stalled the car , any ideas ?

[rogerch]

If they are silicon plug leads, which thet probably are, and more than 2 years old replace them, may not be the cause, but at least it's a possibility eliminated.

[Wilf]

That was my first thought - my new NGK leads arrived today, though judging by the weather will not be hot enough ambient temp to get the chance to test it for a while .

[andydclements]

The wires to the dissy are normally quite limp, they're very flexible with lots of small fibres of copper, that way they can flex easily as the engine moves but the coil stays still.

Heat related misfire could be the coil breaking down as it over heats, it's just another option.

[Wilf]

I did wonder about the coil, but the misfire seems too "regular" thats also why I do not yet suspect a failing fuel pump, it does not randomly miss but feels just like a single cylinder dropping. If I could recreate at home I'd whip the leads off one at a time and catch which one it is. Bit harder in a traffic jam in Bournemouth!

[andydclements]

I had a small motorcycle (100cc) which gave me this sort of issue years ago. When I'd be on my way to and from the college it would be fine some days, others it would get part of the way and then stop without warning.

I tried various things, eventually had the magneto coil checked and it was breaking down under heat, so cold days it was fine, warmer days or days when I got stuck in a bit of traffic it would over-heat and I'd end up pushing it.

[molemot]

The wires to the sensor inside the distributor are very flexible...but they can also wear through their insulation where they go through the distributor itself, which can give very odd misfires.

[Wilf]

Managed to get it good and hot on Friday afternoon and lo and behold Mr Misfire crops up again, however this time I'm on my way home from work so able to recreate on the driveway. No 1 is the culprit, plug looks to have been firing OK judging by the deposits (and by behaviour - this is only intermittent when hot). So, new plugs and leads and we'll see how it goes. Added ,mainly as it can be useful to see how these problems are evntually fixed when doing forum searches.

[Wilf]

New plugs and leads and problem gone. Old ones were not really that old by age or mileage (< 18 months) but don't really care as it goes great now. Traffic jam this morning proved it!