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Technical Mk2 misfire when accelerating after over-run. Help!

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Technical Mk2 misfire when accelerating after over-run. Help!

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NclePunto

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Apr 14, 2011
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Hi, first time poster here and I have been looking at this really helpful website for a good few weeks after occuring problems with my MK2 2001 Punto 1.2 8v ELX. Had this beautiful car for just under 2 years and it has been running effortlessly until a couple of weeks ago. It has 69000 miles on the clock and we have no engine management lights on at all.

Our car misfires on acceleration after over-run (only when it is hot) when you ease off the throttle the misfire sometimes ceases and the car runs normally again. Sometimes you could drive for a few miles and nothing occurs.

We have changed the spark plugs, HT leads, both ignition coils and the car has been plugged in and the only hard fault has been to change the map sensor which we have done. The Head Gasket was done a year ago.

If anybody could enlighten us on a potential solution it would be more than appreciated (y)
 
As it happens only when the engine is hot it might be the lambda sensor. They can be working within normal range (so the ECU is happy) but still giving the wrong signals for good fuel mixture. The correct PC software can see the Lambda voltage trace so it can be evaluated.
 
Thanks for that White. Would i not get a fault code if the lambda sensor was playing up though?
 
If you have a missfire and no warning light, then I would consider the Lambda (O2) sensor to be suspect.

This is because the lambda should see something odd from a missfire, unburnt fuel frinstance, and should throw the light.

It will be possible to get the lambda checked with an Examiner clone.

Cheers

D
 
If the engine is running rich such as when the lambda isnt signalling properly that can also cause a missfire. You need to get the voltage trace with view to replacing the lambda. If it was cheap I would say replace it anyway & see but £80 plus labour is a bit steep to go guessing with.
 
Thanks very much to both of you, WhiteSei and rallycinq. With both of you suggesting this looks like I'll be buying a new lambda sensor. Thanks again for the quick responses, brilliant posters.

However if anyone else has any suggestions, I'm not ruling anything out.
 
thanks again whitesei & rallycinq - will get Lambda sensor checked before replacing it. Looking forward to a smooth running Punto again.
 
Quick update - just changed/replaced the lambda probe from a scrappy. Do i need to reset the ECU and if so how?

Edit - Another update. To reset the ECU i just disconnected the battery and left for 15 minutes after I had replaced the lambda probe/sensor. Took it on a little test ride and nothing seems to have changed. Back to square 1 it seems. :bang:
 
Last edited:
Its needs the ECU codes looking at.

As we said dont rush in and a used O2 sensor can be worse than the one you replaced.
Exhaust popping usually means an air leak (exhaust manifold area) but when it happens on a fuel injected engine it means rich running and air leak. It could therefore be many things. Lambda, crank/cam sensor, faulty coil, something we didn't think of, etc.

See http://www.lambdapower.co.uk/diagnos...stic_index.asp
 
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