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"theoretically, the advantages of this type of system is
reduced coil loads, better spark voltage and the ability to support
big-horsepower levels without misfiring. Unfortunately, when these
multi-coil systems age they become troublesome. Plauged by misfires,
failing coils and general rotting and corrosion of the connectors,
this reduced maintence system is often the cause of alot of trouble.
My experience with coil-troubled cars is that disturbing the
factory installation can cause problems. After changing a set
of spark plugs on an RB25, for example, it is not unuasual for
coil-related misfires to surface. This is extreamly frustrating.
This very situation once occured with Susan's old 180sx. It was
a light misfire that eventually turned into a full bore chug after
a couple of months. She first described it as the car beginning
to chug at traffic lights in the morning, which in some instances
caused the car to stall. This was embarrasing and potentially
dangerious, paticularly if it was at a busy intersection.
I then drove the car to idebntify the problem, only to find that
it would never misbehave for me. The engine ran like a Swiss watch
the whole time I was behind the wheel. A cold morning was required
to identify the dielemma. After a couple of kilometeres, there
it was; a clear misfie started. At around 60km\h the engine suddenly
dropped onto three cylinders and failed to recover as I pulled
up to the traffic lights.
With the Nissan idel air-control system doing it's damnedest
to keep rthe engine from dying, th battle was a loss for the engine,
as it spluttered and stalled. The first turn of the key it restarted
and, as if by magic, ran on four cylinders for a few seconds before
the whole frustrating process restarted.
After about 10km or so of driving, the problem completely disappearedl
the four cylinders fired the whole time, regardless of wether
the engine was idling or at full load.
This scenario should be fairly familiar to a lot of S13 Nissan
owners, but also contains a few clues for owners of other makes
eqipped with multi coil packs.
Realising that the problem wasn't going to fix itself, it was
time for a brief pull down and inspection of the Nissan ignition
system. You must be very carefull of, if working on these systems,
the plastic connectors on the coils, which have been affected
by years of heating and cooling. They become brittle and shatter
at the slightest knock, so carefully prise them off the coils.
The coils themselves, and their associated insulator boot that
reaches down onto the top of the spark plug, collect a fair coating
of carbon and general grime throughtout the years. Part of it
is from grubby mechanics fingers, and part of it is from the general
crap in the Japanese air. While this wouldn't normally be such
a problem, the body of the coil is supposed to be insulated and
carbon is a good conductor of electricity.
Once the effort to fire a spark plug increases - such as with
worn spark plugs or high- demand engine conditions - the spark
will take the simplest parth out of the coil pack. In this instance,
the spark was travelling out of teh tip of the coil and then through
the coating of the carbon and the coil body itself before jumping
to the wall of the spark plug tube. With the spark plug recieving
no spark there is no combustion occuring and, hence, the misfire.
Once the engine began to warm up and the cylinder temperatire
increased to the point where the spark plug decreased in effective
resistance, the problem dissapeared and the spark again started
coming out through the plug.
Fixing the problem is no more of an issue than removing the alternative
path for the spark to leave the coils. This involved removing
each coil individually and wiping them down with a rag dipped
in a solvent (in this cast I used a simple spray on degreaser).
With some elbow grease, each coil comes up like new, with a glistening
red boot and a black shiny body. You will be surprised at how
much dirt and grime can be removed frin them using this simple
techinique.
Before reinstalling the coils, it pays to give them a light coating
of silicone spray. This not only lubricates the threads in the
coil mountings, but also acts as a further insulator against the
spark trying to wander off somewhere. Spending 30 minutes performing
this type of maintenance turned out to be a good idea; not only
didi the idle quality of the car improve, but also did the car's
mid-range urge, due to the odd light misfire being eliminated.
Regardless if the make or model of your car, if it is equipped
with plug-mounted coils then this is a good way to ensure peak
engine performance.
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