Xantia II 2.0 16V - Petrol smell from the exhaust

[lancia58]

Hi

This problem has been around since I bought the car. I did the following but nothing helped.

1) Changed the spark plugs
2) Oxygen sensor
3) Air filter

At the last time I measured the HC it was 130.

I noticed that when I press the gas pedal ( at neutral ) all the way and release it at once a slight backfire is heard at around 3000 RPM. The backfire never appears on normal drive though. Any suggestion how I can track it down. I have a Lexia, can the readings of the various parameter be used to track it

Thanks
Zohar

[Mandrake]

Is it down on power ?

HC of 130 is very high. Either the cat is dead or you have a misfire. (Or both!) A misfire can cause a backfire when you snap the throttle wide open, so I would check for misfires first.

A strong petrol smell from the exhaust suggests an ignition misfire not an injector (lean misfire) problem. Also be aware that driving the car with an ignition misfire can permanently damage the cat by overheating it.

Did any of the spark plugs show signs of fouling or a significant difference to the others ?

Have you done a cylinder drop test and tested the strength of the spark for each cylinder ?

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Unfortunately on an old ECU like those in a Xantia a Lexia probably won't give you a lot of help in troubleshooting as the ECU won't have misfire monitoring.

Coil charge times and oxygen sensor reading under hard acceleration will give some clues but are not conclusive on their own.

[lancia58]

Hi

The coil pack is new. Can a bad cat be the cause for smell of a petrol at the exhaust ? On top of it the bumper right above the muffler is a bit black, looks like a carbon built up

Thanks
Zohar