Xantia V6 Exclusive misfire

[Harlequin]

Hi , well some of you may know I am now the owner of a red V6 xantia exclusive! woohoo!

but on the way to her MOT, picked up a misfire :

heres are screen shots from lexia

the restard is varying a lot! but the click test from the coil pack(s) passed?

[CitroJim]

Congratulations

If the coilpack was the cause it is likely the EML would illuminate and a fault be logged... That has been my experience but there's always an exception!

Most likely cause is worn plugs, plug wells full of oil or open-circuit HT leads to the rear bank...

The plug well nearest the oil filler cap has a habit of filling up with oil.

Simon (Mandrake) has looked at this very same issue in great depth and it's worth searching out his old posts on the subject.

I'm sure he'll be along soon with all the information you will require to resolve the issue...

[Harlequin]

upon reading mandrakes short thread - I have now ordered some Bosch FR8KDC plugs!

[mickeymoon]

upon reading mandrakes short thread

Where is this mythical item?



Sent from my SM-G925F using Tapatalk

[Stickyfinger]

upon reading mandrakes short thread - I have now ordered some Bosch FR8KDC plugs!

I use these as well....also chosen after the reading of the mythical tome

[Mandrake]

The Lexia won't be much use in diagnosing a misfire on the Xantia V6 unfortunately - the ECU is too "simple" and has very limited diagnostic ability. Although a coil primary fault would probably show up in the charge times for the coils, any sort of secondary fault (which is far more likely) like an open circuit spark plug lead, broken insulation in a spark plug lead, faulty spark plug, oil in the spark plug wells etc wouldn't be shown, and in my experience, isn't shown, as the small variations shown on your screenshots look normal to me.

I've "only" had two Xantia V6's, but in both cases they have had intermittent misfires that were hard to track down that turned out to be largely due to worn out spark plug leads to the rear bank. The wires break internally inside the insulation (with no external visible signs) near the rear bank where the wire goes around the rear of the intake manifold and in the right hand side to the cassette, due to poor cable routing design. (The cable is bent too sharply and pulled too tight as the leads are a bit too short from the factory)

The internal break connects/disconnects in response to engine vibration and twisting of the cables. When the wire is not touching together inside the cable the spark has to jump the gap inside the cable and this considerably weakens the spark leading to misfires. On my current V6 it was well down on power when I first bought it and also had a broken plastic guide mounting for the spark plug leads that let them flop around a bit.

I discovered by accident that if I wriggled the spark plug leads around a bit the car leapt into life and the performance was normal for a few days, then it went bad again. Another wriggle of the leads and it was good again. This was my weekly ritual for a few months until I got around to replacing the spark plug leads and repairing the broken guide. Problem solved!

Another way they can fail is its super easy to pierce the insulation of the spark plug leads in the plastic guides due to the wire being a tight fit in the guides and being punctured by the teeth in the guides. If you or someone before you has had the plug leads in and out a few times there is a chance the insulation is damaged.

I've also had a faulty coil pack on both V6's but the symptoms are more subtle and in my case at least the coil only gave problems when it got hot, so if you have a misfire that is only there when the engine is hot I'd suspect the coil pack, but if its there even when cold I'd suspect the spark plug leads and/or spark plugs!

As the spark plug leads are much cheaper than a coil pack I would replace both the spark plugs and the rear bank spark plug lead cassette first and see how it runs, and only replace the coil pack if the problem is not solved. While you're there be sure to clean up any oil in the spark plug wells. If there is only a small amount soaking it up thoroughly will probably last you a few years but if there is a lot of oil you'll need to reseal the cam boxes!

[CitroJim]

upon reading mandrakes short thread

Where is this mythical item?