Quote:
Originally Posted by aardvarkash10
Hey Dave - In the spirit of friendly discussion and to agitate my grey cells a a little, here's my tuppence in response - sorry for the threadjacking everyone else!
Yup. Any airflow will reduce the under-bonnet temperature overall.
My point was there will be very little airflow over the ignition module so won't provide much, if any cooling effect. Also we've been having a heatwave here recently (30+++C) so it seems very much temperature related.
This is of course correct. The issue is whether its relevant. Its not.
Funny you should mention it but it is relevant - the fault disappeared above 40mph when the coil is most likely to be in the resonant "window"
Perhaps, perhaps not. Since the switching is effectively digital, the output transistor is either on or off. Sans a temperature affected junction or component in the output section and resulting loss of current, the output voltage of the coil will be unaffected.
This was my point in the first section - elevated temperatures are causing the problem
This makes two assumptions - the mixture at cruise is weak/lean (probably not - it should actually be near ideal 14.7:1) and that there is a resonant frequency issue with the coil at a specific road speed - there isn't. In any case, the coil is probably capable of around a 25kv output. At stoichiometric ratios, the ignition voltage required is typically between 5 and 8kv. Lean, this may double (at worst). All this from personal experience with lots of different vehicles, oscilloscopes, and problems to be fixed.
Resonant frequency - see above. Cruise mixture - almost certainly higher than stoich, between 16:1 and maybe even 22:1 - very lean in other words!
Part of the "raison d'etre" of manufacturers using the L-Jetronic was its ability to be retro-fitted easily to enable more engines to be "lean-burn" which was all the rage here in the mid-late 80s before catalytic converters became mandatory in 1992
https://en.wikipedia.org/wiki/Lean-burn
If you have a read of that you'll see the point i'm getting at.
Totally agree. |
That's better - got to the end of the "quote" bits! Haven't sussed how to do individual quotes like that on this forum yet, hence the italic typing!
We've both arrived by slightly different routes at the same probably conclusion for this, neither is right or wrong in the methods and/or clues used. We're just interpreting some things in a different way and from a different perspective but still seeing the same picture.
For now though, i'm going to put my brain cell back in its jar and hit the pit
