V12 misfire and dropping rev counter

Per

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I have a misfire which varies in severeness.

Also at about 4500 - 5000 rpm the tacho drops to zero, picking
up again once revs drop to about 4000.

It has a ReOpus ignition amp.

I use NGK Iridium plugs, previously I have run these with the
engine being turbine smooth.

Anything special to check before I start going systematically
through it all? In particular the tacho dropping indicates to
me I have a general problem possibly in the low voltage
circuit?
 

JimboV8

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Checking the ground points would be a good place to start. Does it happen when cold, if not then a cable is breaking down when getting warm possibly.
 

Per

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It is worse when hot and yes I have started to make a new injection harness and then follows the ignition harness. have to accellerate that plan.
 

Per

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An update. I eventually remembered that I had similar issues a few years ago after fitting a new ignition pickup (aftermarket type). I reverted to the original which pretty much cured it in conjunction with the ReOPUS amp. So I believe the original pickup is finally giving up the ghost. As the car is hibernating I have sent off the amp for an upgrade to hall effect pickup.
 
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