Xantia diesel - power then no power

Johnno · Post by **Johnno** » 23 Apr 2006, 18:38

Hi. Long time, no post. Good to see the forum is still going strong. Unlike the 2.1 Xantia - which goes but often not that strong. I seem to have an intermittent fault with fuel delivery whereby there are days - or parts of days - when it pulls like a train and days when the proverbial rice pudding is not in any danger. I say it's fuel as, when the car is in "I really can't be bothered" mode, it is almost impossible to get the usual diesel overfuelling smoke on full throttle. The turbo eventuall kicks in, but is sudden and not progressive.

I've looked at the throttle sender unit, which I assume is some kind of potentiometer, but it is a sealed unit. Is this the likely cause of the fault or is there something else (not the ECU or pump, I hope!)?

I've not been able to show any correllation with temperature and the throttle bowden cable outer sheath seems well positioned.

Any ideas?

John.

AndersDK · Post by **AndersDK** » 23 Apr 2006, 19:03

Hi John -

Sounds like you have had an XUD propelled Citroen in your hands before your 2.1TD ?
Anyway - they all suffer from the same selection of common problems - whether or not they are crammed with ECU, sensors and electronics.

Fuelling problems :
air leak on suction side
air leak on return lines
burnt out (hot running) fuel cut-off valve coil
general wear in pump causing over-fuelling (needs the fuelling screw set back a bit)
TD :
pressure signal hose from intercooler ruptured
same hose clogged with condensed oil

And then the electronics - but very rarely the ECU. Its incredibly reliable.

I'm sure others can add to the list

jeremy · Post by **jeremy** » 23 Apr 2006, 20:35

You mention the potentiometer - which like all of its kind can wear but really is easy to check with a multimeter - disconnect it annd connect a meter between the wiper and the resistance- and measure its resistance - move the thing through its full range and look for hesitstion and rapid meter movement - if you've got rapid uneven movement its knackered and you will have to replace it (or perhaps overhaul it by opening it, and bending the wiper.)

BonceChops · Post by **BonceChops** » 23 Apr 2006, 22:44

By the way the accelerator position sensor is well over £200 from Citroen

Post by **Peter.N.** » 24 Apr 2006, 09:50

Have you changed the fuel filter lately?

BonceChops · Post by **BonceChops** » 24 Apr 2006, 10:37

On the 2.1 there is supposed to be an inlet pressure sensor that connects to the gearbox side of the inlet manifold. If you look on the Citroen pr-net it shows it. On all the ones I have seen there is a blank in the hole where it should be. Does anyone know if there is an inlet pressure sensor on the 2.1? If so where is it. Your problem could be that the ECU is not increasing fueling as the turbo pressure increases causing your lack of power. The injection pump is totally 'fly by wire' with no pipes or accelerator cables going to it, only a multicore cable, so the usual check of the turbo pressure pipe to the pump can't be done.

Post by **CitroJim** » 24 Apr 2006, 12:40

The BOL suggests that the 2.1 has an EGR valve. Now we all know the BOL and its accuracy but if it does, then this has to be a prime suspect. I believe they can be easily rendered inoperative with very little detriment.

What about the timing sensors? I saw a 406 with a 1.9TD ECU controlled pump exhibit much the same symptoms and that was caused by the timing sensor.

Johnno · Post by **Johnno** » 24 Apr 2006, 16:16

Thanks for the replies guys. That gives me quite a bit to go on. And for £200, I'll definitely be looking into dismantling the throttle position sensor - the words "no user serviceable parts inside" just incite me to try harder!.

I'll keep you posted.

BonceChops · Post by **BonceChops** » 24 Apr 2006, 17:49

citrojim wrote:The BOL suggests that the 2.1 has an EGR valve.

It has yes. How can this effect the engine running please?

Post by **CitroJim** » 24 Apr 2006, 18:02

BonceChops wrote:
citrojim wrote:The BOL suggests that the 2.1 has an EGR valve.
It has yes. How can this effect the engine running please?

The EGR valve bleeds exhaust gas back into the inlet manifold to re-burn it and improve emissions. It opens under certain conditions only, the precise detail I forget.

If the EGR valve sticks open (as they usually do), too much exhaust gas goes back in at the wrong time, diluting the inlet charge and also boost pressure sensing fails to work correctly, hence your turbo not behaving properly and fuelling being upset. An EGR stuck even partially open really upsets performance. It is likely it is happening intermittently to give your symptoms.

EGR valves work in a very hostile environment and thus don't enjoy a long and happy life.

I don't know exacly how but I understand it's not hard to render the whole EGR system inoperative (i.e. permanantly closed) as an aid to diagnosis.

BonceChops · Post by **BonceChops** » 24 Apr 2006, 20:00

citrojim wrote:I don't know exacly how but I understand it's not hard to render the whole EGR system inoperative (i.e. permanantly closed) as an aid to diagnosis.

I made a round disc out of thin shim steel and placed it inbetween the flexi metal pipe and inlet manifold. I had to make it dish shaped and the original clip was a very tight fit afterwards. I have since removed it allowing the EGR to work - or not - while I was trying to find my fault. Maybe I will refit it. I ran the car without the inlet manifold on after I replaced the leak off pipes. I could feel the exhaust gasses coming up the EGR pipe. As the car struggled to idle the EGR was opening and closing.