Citroen xantia misfireing once warm

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nick19800
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Citroen xantia misfireing once warm

Post by nick19800 »

I've been searching for about a week trying tO find what might be the problem and came the conclusion that the coil pack was on its way out but I managed to plug it in to a Bosch diagnostics and I had 3 fault codes all to do with the O2 sensor, but would the O2 sensor cause the mAssive misfire on it own. Also does the ecu store fault codes until there cleared in other words if I had a problem with my coil packs would there be code stored in the ecu as when it was plugged the car was running fine?

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Re: Citroën Xantia misfireing once warm

Post by Carsten S »

Misfires will cause unburned fuel into your exhaust, this may give a O2-sensor fault.
An O2 sensor will usually not give misfires - My 5£ is on the ignition coil. The faultcode will be there, until there cleared, if i remember correct.
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Re: Citroën Xantia misfireing once warm

Post by DickieG »

Rather than just read fault codes what needs to be done is to observe the data-flow, i.e. the information running to and from the ECU, this will allow you to for instance to see what the Lambda sensor is doing, it should once warmed swing quickly from 800 to (IIRC) 100 repeatedly, what it does is constantly adjust the mixture from rich to weak, one end of the scale is weak, the other rich so if the lambda sensor was stuck or swinging too far especially towards the weak end of the scale that could cause a misfire.

The coil pack is a likely suspect as Carsten describes, it could be a wiring fault, difficult to say without further info, what exactly were the Lambda sensor faults?

Reading codes is one thing, understanding what they mean and what's happening i.e. cause effect and remedy is another thing altogether.
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Re: Citroën Xantia misfireing once warm

Post by CitroJim »

The ignition coil is the most likely culprit Nick as for them to fail when hot is their normal failure mode. You don't say what Xantia it is but don't forget that the Turbo CTs (and maybe others) have an ignition amplifier which can also cause this same issue.

The V6's put a fault code in the ECU if the coil goes faulty and brings on the engine management light as well as making the car practically undrivable.

let us know the exact model, age and precisely which engine and we can then confirm...
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Re: Citroën Xantia misfireing once warm

Post by Chris570 »

i've been on the phone with nick this evening, i am 99% its a coil pack as its using excessive fuel, only running on 2 cylindars and as said only does it when hot, i'll be popping over on monday with the lexia to confirm, its a 99 2.0 16v xant
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Re: Citroën Xantia misfireing once warm

Post by handyman »

Looks like the ECU is operating in 'limp home' mode if its only firing on two.

It is worth checking the insulator between the coil pack and the sparkplug as I have seen this a few times. The insulator gets dirty from oil from a cam cover leak, eventually the insulation breaks down and the current from the coil tracks at higher engine revs as it can no longer cope. This is not prevalent on just the 2.0 16V engine but on a few of the PSA engines with the coil pack mounted between the cams. I now keep a stock of new insulators for a few different engines. Check the price from Citroen for the sets! :shock: :shock:

Let me know if you need one or two, as I might be able to help.

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Re: Citroën Xantia misfireing once warm

Post by nick19800 »

I must say a big thanks to Chris570 for taking time out after work tonight to come and help me out with some diagnostics and filling me in with some information about known troublesome areas and other faults that are knocking around the ecu i.e suspension. =D>

Anyhow I ordered a coil pack tonight which Im hoping will cure my problem.

Also any ideas where I can find a break switch pedal as the ecu constantly thinks that my foot is on the brake which could be a contributing factor as to why my cruise control is not working? :lol:

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Re: Citroën Xantia misfireing once warm

Post by Chris570 »

not a problem, its worth taking it off and giving it a clean :)
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Re: Citroën Xantia misfireing once warm

Post by CitroJim »

nick19800 wrote: Also any ideas where I can find a break switch pedal as the ecu constantly thinks that my foot is on the brake which could be a contributing factor as to why my cruise control is not working? :lol:
This may be a contributory cause Nick. On some ECUs if it sees the brake pedal and accellerator pressed at the same time then it sees this as wrong and does not allow correct operation. On yours this may manifest as a misfire. Worth checking...

The cruise brake switch is not the same as a standard switch. It has two sets of contacts - one for the brakes and one dedicated to the cruise control.

If you search out a thread I did long ago on cruise problems the switch and how to fix it is described in good detail.
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Post by addo »

A 16V '99 model will have the cruise type brake switch as standard.

The brake part of the switch is a simple "make" contact and it could be the wiring is pinched somewhere. A mouldymeter is one easy way to check.

Coil packs are easy to diagnose on Lexia; the dwell times are your clue.
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Re: Citroën Xantia misfireing once warm

Post by nick19800 »

The car was running perfectly fine when it was plugged into the lexia but as soon as I left to go home I got about 5 yards down the road and was running crap which is typical so essentially wouldn't the dwell readings be correct as it was running fine when it was reading the data?
Any ideas as to what the correct name for the brake switch is and where I could find one as I'm struggling a bit to locate one.

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Post by addo »

The brake switch is in the pedal base itself. There's a connector upstream on the pedal "arm"; you will have to be upside down in the footwell to really see it.

Normally even a dead/dying coil will show crap reading when cold - you just don't notice the effect until it's hot and loaded up. Getting the motor warm and stalling it up will simulate loading to some extent.

They are overall a simple ECU, so diagnostics/repair is a matter of physical checks first, then basic supply items, then parameters.
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Re: Citroën Xantia misfireing once warm

Post by nick19800 »

Problem solved!!!

Chucked the newish coil pack on along with some new BKR6's and its not skipped a beat.

Thank God, it was driving me mad.

Thanks for everybodys help.

Nick
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