From: "Norbert Wank" <mrv8@dhc.net>
Subject: Vmax ignition trouble solved

Here's some time consuming experience closely related to ignition, which
drove me nuts over the past few days, so I had to blow my trip to Austin
last weekend  :-(


Problem:
right at 4,000 rpm, significant loss of power, rough ride. Repeatable
event, with smooth idle, pick up gas when the throttle is blipped and
revved (even above 4,000 for short term), but did not pull quite as smooth
under 4,000, much worse above 4,000 (takes ages to get close to redline
under load).
model: 95 Vmax, 33k miles, spark plugs about 4,000 miles.

First attempt:
starting with a clean sheet, I replaced all spark plugs (early maintenance)
with no effect.
measured pick-up coil resistance and vaccum sensor output = OK (after
finding them, thanks Mike).
Measured primary coil winding = OK.
Sparks are seen with strobe light on all cylinders. Replaced spark plug
wire and spark caps (with aftermarket ones, just for trial. Genuine Yami
caps are $40 a pop!)
Since it felt like my old KZ when the ignition box went wild, I suspected a
TCI problem. Heat, gas, vibration and moisture is not really a friend of
electronics. Thought I check visually for blow marks (none) and the power
transistor leakage (collector-emitter, all nicely labeled after the box is
sliced open). Resoldered the entire board, eliminating "cold" solder
junctions. No effect.
Replaced TCI unit with known good one (from Vern, thank you, thank you,
thank you, Vern): no effect.
measured secondary coil winding: bingo, front left was open, but still
firing (suspecting voltage arc).
Repeated measurement confirmed prior results.
Installed spare ignition coil (thanks Vern). Much better, yet not
satisfactory results (bummer).
Threatened to take Max to the dealer: immediate cure! That's called "doctor
syndrome. Ran fine the rest of the weekend :-) Put it to the test Monday
morning with high moisture content in the air, to push my luck: positive.
Max runs like crap again.

Since a known good coil is in there, and the original coil proved ok as
well: must be connectivity problem!
Strangely enough, both front coils are mounted on the same sub-bracket that
are bolted to the frame for return current of the coils. But only one coil
checked bad when measured through the new plug wires.
The wire itself has continuity.
After dismantling Max again, I found all four bracket screws rather loose,
picking up enough vibration at 4,000 to yield intermittend sparks. After
tightening all screws, including the ignition coil, the mystery problem was
solved.

Morale: always check the "free and simple" fixes first. Hope it may help
someone someday and save a weekend.

Bert
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