[alfa] V6 Spark Breakup - Part 2 (Long)

["Herbert Neily" <neily@xxxxxxxxxxxxxxxx>]

Hi All,

I'm still experiencing a perplexing ignition signal breakup in 2 of the 6
plug wires in my GTV6.

In our last episode, I wrote:

>After installing rebuilt cylinder heads on my '84 GTV6, I was very
>disappointed by how poorly the engine idled upon the first startup.  I
>verified that my ignition and cam timing were correct.  I discovered a bad
>connection at an injector's electrical lead, fixed it, and engine idled
only
>marginally better.  Using an inductive timing light, I found my #6 plug
wire
>to have a very weak and erratic signal. My plug wires were old, so I
figured
>it was time for a new set. I decided to replace the coil as well.
>
>As of right now, I've got brand new:
>  Spark Plugs (Bosch single electrode platinum - maybe iffy, given the
>recent discussions, though my '87 Milano runs great with them)
>  Distributor Cap & Rotor
>  Bosch Coil
>  International Auto Parts copper core wire set (their Item 23047)
>
>The engine still idles poorly.  Tonight, I used two inductive timing lights
>to check the pulses in the wires.  Plug wires #1 through #4 give distinct
>and regular light pulses.  The #5 and #6 wires exhibit bright, less
regular,
>pulses surrounded by very quick pulses of lesser brightness.  It's as
though
>I've got some kind of signal leakage.  I reinstalled the old distributor
cap
>(which showed no cracks or carbon tracking) and rotor, only to find the
>behavior the same.  I've run the car after dark and don't see any errant
>sparks flying around.  To check the plugs, I swapped my #4 and #5 plugs.
>The erratic signal remained in the #5 and #6 wires.

Tonight's episode:

At that point, I checked the resistance of each new wire.  I found about 2.4
kOhms, measured from one wire connector to another.  Since the wires were
brand new and the resistance consistent, I decided that the problem lay
elsewhere.

I ran through a multitude of  shop manual diagnostics, verifying continuity
and resistance of ignition-related wires from one ignition component to
another.  I cleaned all connectors and grounds.  With all of that checking
out, I began to swap major components from my smooth running '87 Milano.
One component at a time, swapped the following into the GTV6:

Ignition Amplifier (from beneath the ignition coil)
Distributor (including hall-effect pickup coil)
Ignition Control Module (beneath dash, above fuse box)

After swapping each component, I ran the engine and continued to find the
spark breaking up in the two plug wires - though weirdly, the breakup
shifted from #5&#6 to #4&#5 somewhere in the process.  I ended up with all
of the original GTV6 pieces in place.  A digester had suggested using the
timing light to check the coil wire's output - firing at six times the rate
of the individual wires, the coil wire's signal was too fast to evaluate by
that method.  I had checked every other individual element of the ignition
system and still not found the smoking gun.

I was at a loss at that point, so I grabbed my old plug wires and
reinstalled the old #4 & #5 wires - eureka! - the engine idled smoothly and
the inductive timing light showed regular bright pulses in all wires.  I put
the new #4 & #5 wires back in place - the idle went to hell and the timing
gun signal went back to the former erratic mode.  Tried the old #4 & #5
wires again - smooth idle and clean signal.

Though I found it hard to fathom, I assumed that my new wires were
defective.  I called International Auto Parts and they agreed to send out a
new set of wires.  They suggested that, in the meantime, I should check the
resistance of the wires while connected to the distributor cap - perhaps I
wasn't getting good contact at the cap.  Since I'd already tried two
different manufacturers' distributor caps, I was a little skeptical, but I
went ahead as suggested, going one better by using a spare spark plug to
measure total path resistance from the inside of the distributor cap to the
center electrode of the plug.  Each cap-wire-plug assembly's resistance
consistently measured about 5.4 kOhms.  I installed yet another brand new
rotor and distributor cap and found the same signal breakup in the #4 & #5
wires.

Today, my replacement wires arrived in the mail. I installed the replacement
wires and eagerly started the car...... only to find the #4 & #5 wires'
signals breaking up and the engine idling poorly - arrgh!  I'll be
sheepishly sending my very low mileage replacement wires back to IAP on
Monday....

Color me perplexed.   The only other information I can offer is this:  My
old plug wires were a set of blue fiberglass-core wires (now discontinued
for the V6, was IAP Item No. 23039).  These wires' resistance varied
proportionately with length.  Tonight I checked the old #4 & #5 wires'
cap-wire-plug resistance and measured 14.1 & 15.8 kOhms, respectively -
roughly three times the resistance of the newer copper-core wires.  Can
anyone offer an explanation of how higher wire resistance could overcome or
mask a signal breakup caused by..... something else?  The shifting of the
breakup, from the #5&#6 to #4&#5 wires, does suggest something odd going on
in the primary side of the system as opposed to the secondary side, though
I've changed out virtually all of the primary side system that's devoted to
generating the triggering pulse for the secondary side.  I have not tried
swapping the Milano's FI ECU, since I can't envision it having an effect on
the triggering of the ignition system - though I might give that a shot
tomorrow.

Thanks for reading and thanks for any input y'all would care to offer.

Bert Neily
Raleigh, NC, USA
'84 GTV6 with unruly electrons
'87 Milano donor
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