Fiat Dino Forum (FDF)

I just spent a worrying day with my 2.4 Coupe - only firing on 5 cylinders for much of the time, after finally getting home and some diagnostics I traced the fault to a bad sparkplug - swapping it between cylinders the problem followed the plug. That's the first bad plug for me in about 30 cars and 40 years. Ahh well, always a first time.

So I'll get a new set of NGK BPR7EIX, since I'm using Adrian's Bosch ignition module and these are the best plugs for any transistor ignition. While swapping plugs and wires around I realised my set of ignition leads has NGK 5Kohm caps, the BPR7EIX are 5Kohm plugs, so maybe I have too much resistance and I should make up a new set of ignition leads with new caps.

Before I go and source everything - what colour were the original wires/leads? Right now mine are all red - is that correct? Seeing as all colours are available I might as well buy the right one.

Thanks,

-Richard

I would not be to concerned about the resistance of the cap and plug. A good ignition system will have no problems with that what so ever. It has hardly any impact on spark output but it's there to reduce the 'noise level' of Radio Frequency Interference and it suppresses ElectroMagnetic Interference.

If you want to replace your HT-leads anyway i would go for a good quality resistor type wire-wound type of lead instead of the copper core wires with resistor caps. In the US it should be no problem to have some MSD leads made. They are good quality and the correct red color. Only drawback is that they are slightly large in diameter, 8,5mm instead of the original 7mm. Magnecor is also a respected manufacturer but there are other good brands as well.

I have some new custom set's laying around as well but for you it might be easier and faster to have them made somewhere around the corner.

Thanks Stefan - especially for confirmation re. the resistance. Searching through the NGK catalogs they make about 50 types with a 5k resistor and only 3 without - so I guess I will stick with the resistor.

I always make my own ignition leads - The Green Spark Plug company has the nice wire-core 7mm cable
https://www.gsparkplug.com/7mm-ht-ignit ... c-red.html

cheers,

-Richard

Hi Richard,

The HT lead you show in the link is a copper core lead. That type of lead should be used in combination with resistor caps you mention to have some EMI and RFI suppression. Works OK'ish in my opinion.

I would instead go for the 'ferroflex' lead they sell at the green spark plug, that is a spiral wound type of lead. This lead itself has a certain resistance per foot and has good noise suppression by lead design (1kOhm per foot for example) and can be used with normal rubber boots. Using this type of lead there is no need for the resistor caps.
That 'ferroflex' is the same HT-lead design as used by MSD and Magnecor.
Just google 'spiral wound ht lead' and you will find some pictures that show the different layers of material used in a spiral would lead.

Some additional information about ht-leads and resistance: https://www.magnecor.com/magnecor1/truth.htm

Thanks Stefan - some good info there on the Magnecor page.

I guess my confusion about a sensible resistance comes from knowing that the iridium sparkplugs work well in our cars because the smaller electrode allows a spark to initiate at a lower voltage. Therefore concerned that too much resistance in the system could negate that benefit. 5Kohm plug + 5Kohm cap + 3Kohm wire....seems like a lot, but I guess the voltage available is huge so maybe it's irrelevant.

-Richard

I'm happy with simple NGK BP7ES and standard cables/caps. The very high voltage of the Dinoplex renders them less important.