Punto Mk2 16v: engine cutouts while idling?

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Jan-Sebastian Winckelmann - 19 Apr 2004 18:20 GMT

Hi,

my Punto Mk2 ( 16v ) shows an annoying behavior. While idling
the engine has random and frequent cutouts, i.e. a cylinder
isn't fired. This leads to a mildly shaking car and a not very
healthy sounding engine, especially when the engine is warmed
up. While driving I don't notice any cutouts.

My authorized garage wasn't very helpful. They said that the
computer diagnostics doesn't show any problems and they have to
replace some expensive parts trial and error to locate the
problem ( throttle valve or electronic control unit ). It's
obvious why I'm not very happy paying around EUR 500.- for such
a proceeding.

Are there any known issues with this engine that could cause the
problem? At least it should be clear if the problem is connected
to the fuel injection or the ignition. I suppose that not fired
petrol could cause some damage to the catalytic converter. But
the exhaust emissions doesn't smell of patrol ...

I plan to switch to an independant garage which may has some
more motivation to locate the real error, not just exchanging
whole units. What should they check? Any hints?

Thanks in advance!

Bye,
Jan

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Jan-Sebastian Winckelmann
Henstedt-Ulzburg, Germany

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ato_zee@hotmail.com - 19 Apr 2004 19:33 GMT

On 19-Apr-2004, Jan-Sebastian Winckelmann
<20040419.3.jwinckelmann@spamgourmet.com> wrote:

> Are there any known issues with this engine that could cause the
> problem? At least it should be clear if the problem is connected
> to the fuel injection or the ignition. I suppose that not fired
> petrol could cause some damage to the catalytic converter. But
> the exhaust emissions doesn't smell of patrol ...

As it happens when idling during tickover I suggest you get one
of the little neon ignition testers that goes on top of a plug, in
series with the ignition lead, these are good for showing no
spark. In practice, as they are difficult to use in daylight, I use
a timing light in series with the coil. Of course this falls down
if you have a badly carbonised plug that is bridging out and
not firing. Other than that proviso, if the light flashes while the
engine misses it is unlikely to be a vibration induced electrical
intermittent or a bad coil.

I have met a Fiat with a short length of hose buried behind
the engine between the fuel pipe from the tank, and the fuel
filter which was on a bracket. It had a split, and at low revs the
fuel pump was pulling mostly air, at higher revs it ran ok.

Intermittents are always a challenge needing methodical
deduction, and don't forget Fiats are not noted for good
electrical grounds.

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Jan-Sebastian Winckelmann - 30 Apr 2004 17:23 GMT

>> Are there any known issues with this engine that could
>> cause the problem? At least it should be clear if the
>> problem is connected to the fuel injection or the
>> ignition. I suppose that not fired petrol could cause some
>> damage to the catalytic converter. But the exhaust
>> emissions doesn't smell of patrol ...

> As it happens when idling during tickover I suggest you get
> one of the little neon ignition testers that goes on top of
[quoted text clipped - 6 lines]
> misses it is unlikely to be a vibration induced electrical
> intermittent or a bad coil.

Thanks for your advice. My independant garage was able to locate
the problem. It was a faulty spark plug, not easy to find. The
spark plug looks almost o.k. but the isolator looks brownish
where the metal part of the plug starts, there are also very
tiny pieces of melted metal visible. The sparks must have
choosen a strange path. My authorized garage still is convinced
that their computer should have been able to locate this
problem.

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Jan-Sebastian Winckelmann
Henstedt-Ulzburg, Germany

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