Ah, here's the article Will was talking about!
>"One time a fellow with an XJ6 came into the shop with the following
>problem. The car ran fine at idle, but would misfire badly under hard
>acceleration. Interestingly, it would run fine under hard acceleration, BUT
>ONLY IF IT WAS IN REVERSE, moving backwards.
>What is the explanation?"
For a while, our TR7 would misfire only while turning left. It turned out to
be a loose connection to the ignition switch in the steering column, which
was exacerbated by turning the steering wheel left.
> What was the explanation? The casing
>on the old coil had developed a leak, and the liquid insulant inside had
>partially drained out. Hence, when the car accelerated forward, the liquid
>went to one side of the coil, resulting in a short at the other side, which
>in turn caused a weak spark and a misfire. When the car accelerated
>backward the liquid of course went to the other side and protected from a
>short, resulting in no such misfire.
Sounds perfectly reasonable. Assuming that the front is the high voltage
side and the problem was a line-to-ground (case) fault (as opposed to a
turn-to-turn fault, which would occur at whatever side the oil wasn't),
it's entirely possible.
For those who don't believe, here's a somewhat related high-voltage story.
Our HV lab was doing some tests on transmission-class cable (real big stuff)
using deionized water as a semiconductive, stress-grading material that
helps to even out the voltage distribution between where the grounded metal
sheath is stripped off to where the insulation is stripped off and the outer
conductor is exposed <kill techno-babble copy writer: ...wah!>. If you're
willing to take the leap of faith that such measures are necessary (we deal
with terminations as long as 20 ft!), you should be able to appreciate why
we'd use water - it's commonly available, and takes the shape of whatever
size cable we throw in. Anyway, the water heats up quite a bit under
voltage, and we're too cheap to have a system that circulates and cools the
water, so the plastic cable insulation heated up too. Plastic expands quite
a bit when it heats up, so it pushed some of the water out of the top. When
it cooled down between tests, the water settled down to a level below
where the inner conductor was exposed, so there water no longer had a good
contact with the high-voltage conductor. And the next time we energized the
sucker.............BANG!
Next time we're going to borrow an overflow bottle from one of the fleet
vehicles.
Jody
jlevine@rd.hydro.on.ca - Toronto - '80 TR7 drophead
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