Citroen XM V6 Bad Running

Joe T · Post by **Joe T** » 15 Nov 2005, 09:54

Dont laugh I know, but I have had this car for years and its been a good workhorse, about a year ago slight misfire or flat spot started, and it gradually over the year got worst, during this time I have replaced what I can, this includes the following

Dist,cap,rotor,leads,plugs, Coil, Transistorised ign module.
Idle speed regulator, fuel pump, fuel pressure reg, fuel dampner.
Ign ECU, Inj ECU, throttle position switch

Its a 92 V6 SEI 12v Manual Estate.

It never has the fault when cold but as the needle reaches the 90' mark it will start,
I never loses Idle, and can drive through it to about 3000
Its a throttle position fault rather than revs related but comes in on normal driving at 1800 RPM. its awful in slow moving traffic etc.
Its a smooth cut like a revlimiter, you can feel the engine move on the mountings, it feels like it looses several cylinders.

The Citroen Diagnostic computer displays no fault found or recorded.
I have kept driving it the hope it will die and the fault can be fixed.

Its had the mod to the block connecter under the LHM resovoir, and I have broken and cleaned most engine loom connectors.
It has been suggested to change the Lambda sensor, honest truth is I cant find it? I have followed the exhaust back and found nothing, I had to change the starter and I had a good look round etc.

Does this ring any bells with other V6 owners? Am I the last one left?

Post by **Peter.N.** » 15 Nov 2005, 11:52

I dont know to much about modern petrol engines as I have run diesels for 20 years or more, but if it has electronic engine management, fly by wire type, it could be a 'noisey' potentiometer,the thing that the throttle cable is connected to, like the volume control in an old radio, it could have a 'dead' or intermittent spot on it.

Joe T · Post by **Joe T** » 15 Nov 2005, 13:53

I did change the throttle potentiometer, also the MAP/F Sensor that detects manifold depression.

I alos have a diesel Saxo sort of agree on the simplicity of diesels, I cant beleive I cant find the Lambda Sensor!!!

Thanks Anyway

NiSk · Post by **NiSk** » 15 Nov 2005, 15:33

According to the parts list, it's IN the top of the cat, at the front top.

Check out at:

http://ipcxm.free.fr/xm1/environement%20moteur.pdf

page 921.

P.s. ther are lots of other goodies on

http://pepon1.free.fr/

A French site.

//NiSk

Joe T · Post by **Joe T** » 21 Nov 2005, 22:17

Wow looks like I may have to take the CAT off just to check how many wires it has to order one. What a nightmare, especially as I cant tell if its faulty, the CO seems fine?

andmcit · Post by **andmcit** » 21 Nov 2005, 23:27

Joe T wrote:Wow looks like I may have to take the CAT off just to check how many wires it has to order one. What a nightmare, especially as I cant tell if its faulty, the CO seems fine?

seems a bit drastic

Who are you dealing with - Indy/Cit/Exhaust supplier?

The sensor is easy to trace off the top of the cat - the 2 multi plugs come up and meet beneath the LHM reservoir.

The citroen parts database states for a 2,975L [without an air temperature sensor];

Part No: 1628 R9

OXYGEN PROBE
RED AND YELLOW CONNECTORS

Part No: 1628 1G NFP

OXYGEN PROBE
- SINCE RPO No. 06049
CONNECTEURS ROUGE ET BLEU

For INJECTION AND 2,963L AND 2,975L AND (J):

Part No: 1628 R9

OXYGEN PROBE
RED AND YELLOW CONNECTORS

Have a look see what the twined multi plugs are coloured and you're getting somewhere!

Mind, there's no guarantee the rusted thread of the old sensor will actually come undone off the cat...

Hope this helps.

BTW, a mate ran a 3.0SEi manual without a lamda sensor on the car and never had any flat spot...

Andrew

Joe T · Post by **Joe T** » 24 Nov 2005, 12:23

Thanks, very helpful and in some ways made my mind up not to replace it as form what you say it does not sound as though thats the fault, my fault feel like a leads or coil type fault, very harsh loss of cylinders causing gear lever to shake etc.

It is a shame becuase the old girl has served me well, and its the only thing wrong with it?

Any other bits I should consider replacing, my mate has suggested engine loom.

Cheers

Joe

andmcit · Post by **andmcit** » 24 Nov 2005, 16:03

Joe, are you ABSOLUTELY SURE the replacement parts are 100% or NEW. Won t be the first time a duff part has been tried and trusted as OK thus hindering proper diagnosis and/or repair...

I'll have a mull over they problem and have a poke about on my V6 and my documentation and post if something hits me!

The revs range abrubt on/off should be a clue - the throttle position switch you mention I presume is the butterfly on the induction?

Andrew

Joe T · Post by **Joe T** » 24 Nov 2005, 16:40

Honest truth is no not all new, but from variuos problem free cars, my only comment is the fault hasn't changed at all during in the last year!

It started on a journey through france where I lost acceleration and idle, like a smooth cut rev limiter, in desparation I pulled into a garage and bought some brake/carb cleaner and squirted that through the air bypass valve and into the throttle body, the idle started running again but I was left with the intermittant running under load. Over a period of time its become more predictable.

I started my replacement quest with the bypass idle valve, and havent stopped since, only running out of things to change. I have access to some citroen tools like the computer as I used to work for them in the GS to CX period, I have kept the faith etc.
But the computer says No fault found.

Is there a timing sensor anywhere? its such a fierce cut in and out, how about ignition switch, I am beginning to sound desparate now............

Any clues would be good,

Cheers

Joe

NiSk · Post by **NiSk** » 24 Nov 2005, 17:57

An old post springs to mind - that was also an XM V6 - try lifting out the LHM reservior (its probably time for a change anyway) and take a really good look at the cabel connectors underneath it. Pull them apart, clean up with e.g. Maplins electrical cleaner and protector, make sure none of the pins are so corroded that they dont make 100% contact, put it all back together again and marvel at your new found reliability!

//NiSk

horrid1 · Post by **horrid1** » 27 Nov 2005, 21:48

"It never has the fault when cold but as the needle reaches the 90' mark it will start, "
Could this be a clue?
Is there some way of bypassing your temperature gauge temporarily?

Ernie

andmcit · Post by **andmcit** » 27 Nov 2005, 22:38

horrid1 wrote:"It never has the fault when cold but as the needle reaches the 90' mark it will start, "
Could this be a clue?
Is there some way of bypassing your temperature gauge temporarily?

Ernie

I was wondering about the temperature effect too. The ECU will adjust the fuel and ignition according to the temperature feed it's receiving from a sender in the water jacket [IIRC there's two sensors an the casting that is a bridge above the water pump on the ECU end of the engine].

The 90 seems significant as that's the normal operating temperature with the thermostat opening.javascript:emoticon('

') The flat spot could be the ECU thinking the engine is hotter and leaning the feed on fuel into the engine thus a lack of power...

Been up to me eyes this weekend so haven't even had a chance to look at my V6 or relevant paperwork yet to verify some of the theorising here!!

All thr best,
Andrew

Joe T · Post by **Joe T** » 30 Jan 2006, 12:57

Well I thought I would update this thread on progress, or the lack of it.

I removed the LHM res as suggested took aparts and cleaned the main engine loom connectors, also noted a couple of wires had been bypassed round the connector.
Also found the Lambda plugs. cleaned them to you never know etc.
Run a meter over the HT leads.

But the fault is exactly the same. I notice above that Temp sensors were mentioned, I tried swapping the two connector's round to see if it made a difference and it did not seem to.

I tried another person in the driving seat, at first he did not notice the fault then when accelerating to 60mph in 5th at about 2500 just as it warmed up off it went, we then went through the list of parts Plugs, Leads, Coil etc. I suggested he moves it up to 80 and it was fine. In slow traffic the problem is more pronounced as its just right for slow moving traffic in second nice and jerky.

So parts I have not replaced, Injectors, Lamda Sensor, Engine Loom, Temp Sensors, Throttle Body.

Any suggestions.

jeremy · Post by **jeremy** » 30 Jan 2006, 19:13

perhaps the answer lies above!

Seriously - don't have much experience of fuel injection - but I always get worried when I find someone has been bridging connectors and tinkering with wiring. Its probably perfectly correct but worth a good look.

andmcit · Post by **andmcit** » 30 Jan 2006, 19:52

jeremy wrote:perhaps the answer lies above!

Seriously - don't have much experience of fuel injection - but I always get worried when I find someone has been bridging connectors and tinkering with wiring. Its probably perfectly correct but worth a good look.

Bizarrely, if I were you, I'd leave it alone!!

This is actually a Citroen mod that's done as an update mod by Citroen dealers upon seeing and servicing the car from new. I've got a technical updates log/manual that covers this as a splice repair!!

Ok, sorry no help, and no further forward...

Andrew

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