The reason that the coil pack can be damaged by faulty plugs, leads or
removing a lead with the engine running, is that normally the maximum
voltage the coil generates is limited by it jumping across the gap in
the sparkplug.
If there is a break in the HT circuit or somewhere else the voltage out
of the coil can go far higher than it's designed to and cause the
internal insulation in the coil pack to fail.
I unplug the injectors in turn instead if i want to do a cylinder test
on a EFI engine.
And, the reason that most ECU's can't tell you theres a problem with the
crank sensor is that it's the crank sensor that the ecu uses to detect
that you are turning the engine over on the starter.
Without pulses from the crank sensor the ECU has no idea it needs to
start generating sparks and injecting fuel, it's sitting there waiting
for you.
A crank sensor generates a higher voltage pulse output the faster the
engine is turning so if it starts to fail it will often fail next time
you try to start the car.
Jim
On 11/07/2012 21:59, Derek Clews wrote:
Thanks Michael,
It was a general recommendation as a preventative from an AA mechanic.
He said the bulk of the engine breakdowns on modern cars can be fixed
by replacing the coil pack or the crank sensor and they carry quite a
number on each van as a result. He said they can be affected by heat
and age. Also they cannot use a computer connection for most cars so
are back to trial and error, backed by experience!
Interestingly, he also said the AA recommend that if a coil pack has
been found faulty and replaced, the plugs and leads should also be
replaced as it is possible a problem with these could cause the coil
pack to fail in the first place. Also rough handling like pulling off
the plug leads when the engine is running can cause problems. (Did
not do that!) Makes the modern systems seem very fragile.
To support his view, the only time we had a breakdown in the old Punto
my son learned to drive on it was the crank sensor that failed.
Basically it drove normally, parked up and would not start again, no
fuel & no spark. But of course the car would not tell you what the
problem was so you are stuck with having to use a garage - that's why
I like older cars! The basic CVH will still run with the distributer
loose, carb faults or whatever - not very well, but it will run!
Still, I am learning new ways...... part of the fun of this
particular project coupe.
Derek
On 11 Jul 2012, at 19:46, [email protected]
<mailto:[email protected]> wrote:
Your information might be correct but from my experience with a 1.6
turbo CVH the weakest link might well be the connector rather than
the sensor itself. Michael
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