[v12-engine] Misfire and rev counter dropping

V12-Engine
1

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 hva 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?–
PEXJC
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2

In reply to a message from PEXJC sent Fri 14 Oct 2016:

When the tach drops, do you lose power? What car do you have?–
The original message included these comments:

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 hva 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?

PEXJC

–
Bill Gutierrez, '61 OTS '73 OTS
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

In reply to a message from Lundabo sent Sun 16 Oct 2016:

I would start with the ReOpus amp. I know it’s upgraded
componentry from the Original Opus, but the failure
symptoms sound identical
Does it do this from a cold start? The Opus starts
playing up once hot.–
The original message included these comments:

When the tach drops, do you lose power? What car do you have?

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

–
Mark Brown 71 S3 Etype
Ohope beach, New Zealand
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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4

Turned out to be a dicey connection in the low voltage circuit. Very difficult to find.

5

That was going to be my guess. My tach was dropping to zero and was accompanied by the engine losing power. The culprit was deterioration of the tach wiring at the ballast resistor that was shorting. Glad you were able to find it.