Technical 1.2 Dynamic rough start

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Technical 1.2 Dynamic rough start

DaveMcT

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The car is 1.2 Dynamic with 60K on the clock. Correctly serviced and not abused.

The engine seems like its running on three when started from cold but its fine when warmed up and mpg is good so not been too fussed about it.

It's had -
new air filter
New spark plugs (though old ones looked fine)
Runs on posh petrol most of the time

The last MOT showed good emissions at 2,500 revs but borderline on HC and tick over.

If it was always running smoothly I would be thinking the catalyst or O2 sensor is failing but that slight roughness on cold start might be a clue. Italian tune ups have not affected the issue.

What does the collective think it could be?
 
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It won't take any notice of the O2 at cold start.

It'll use pre set cold start settings until it thinks the O2 is hot enough to send back a reliable sign.

With a scan tool, even a simple one like Torq Pro, you can watch the fuel status from start up.

It'll use what's called Open Loop until it thinks/knows the O2 is responding properly, then change to Closed Loop, this now means it's using the O2 to trim the fueling.

From a stone cold start, they'll do this within a couple of minutes as the O2's heater speeds up the process rather than waiting for the gases to heat it, like a few years ago.

If the O2 fails to heat quick enough they tend to fail back into Open Loop - System Fault and continue on a rich, pre set setting to get you home.

You might want to measure the fuel pressure, check the ignition by swapping the coils (if you can identify which cylinder is misfiring).
You can try this with the injectors too, see if the misfire moves with the injector/coil.

Something else would be to check the compression.
 
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Try something simple first,
such as spark plugs or HT leads, or just spray the coil packs with wd40 to remove early morning damp.
One of the problems with ECU controlled systems is that all seem to want to dive in to guessing at an electronic or sensor/component fault when it could or more than likely be a simple age old problem of damp or wear.


on that side though, the coolant temp sender has a big input in fuelling when the engine is cold (although I don't think it's the issue you have)
 
Re-reading my OP it does sound worse than it actually is. Its more of a stutter just after startup rather than a full missfire. It might be coils but as they are the wasted spark type I'm not sure that's the cause. A coil would affect both of its plugs but it's not behaving that badly.

Coolant levels are good so compression is not top of the list. But it could be a valve so a compression test should be done. I'll have a look at the coils and get a code reader on the case.

Any thoughts on the MAP sensor?
 
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