HDi K light and revs out of control...

simoncanfer · Post by **simoncanfer** » 25 Jun 2008, 21:27

Today I noticed the engine speed rise of its own accord; as if someone else was pressing the throttle pedal slightly! The K light came on.

Took it to get the code read, which was "primary fuel circuit". Mechanic cleared the fault, test drove it and it didn't recur.

You guessed it, it has now come back, symptoms and K light! Imagine a stuck throttle cable, the symptoms are the same.

Any ideas?

Anyone know of a HDi faults FAQ?

Simon

Xantia HDi 110, 1999

deian · Post by **deian** » 26 Jun 2008, 17:13

It's not an air leak in the fuel delivery pipes is it?

Thats the usual case with the older 2.1td unit with the lucas pumps. Not sure how different the technology is on the HDi units, I know they are higher pressure.

AndersDK · Post by **AndersDK** » 26 Jun 2008, 19:08

Hi Simon -

The HDI works completely different from the early style diesels.
In fact a HDI works much the same way (in principle that is) as a multipont injected petrol.
The most noticeable differences being a much (insanely much) higher injection pressure on the HDI - and still no throttle butterfly.

The injectors are electrically operated and controlled by an ECU on both the petrol and the HDI engine types.

The reason why you get this sort of slow engine run-off would then come from either of 2 facts :
1) the HDI engine management thinks (for any faulty reason) it needs to open the injectors for longer injection times thus providing more fuel to the engine and it then starts to run off.
2) any engine oil bypass problem causing engine oil to take part in the combustion as fuel - a wellknown faulty diesel phenomen

Reasons for these situations I could think of :
In case 1) it could be any electric problem with any electronic accelerator pedal ("fly-by-wire"). Cabling, connector or pedal position potientiometer sensing faults.
Could also be a temperature related problem with the crank-speed sensor. Either a contaminated sensor, a faulty sensor or the sensor distance is out of range to its sensing media (flywheel or whatever it works off)
in case 2) you should start out with a good check of your engine oil viscosity grade and oil type.
For HDI engines there are much more stringent recommandations on engine oil types - than on earlier engine types.
Any faulty sump ventilation or a failing turbo (cold/inlet side) seal may be the cause.
Proof on engine oil fuelling will evidently be a messy dripping wet oily greased intake system.

simoncanfer · Post by **simoncanfer** » 28 Jun 2008, 23:17

deian - the hdi (or at least the one in my car!) has a fuel pump in the tank so at least I'm immune from air in the fuel. In fact it works at a few bar pressure so leaks would be obvious.

Anders - thanks, I'm learning about the HDi, there's quite a lot of info about the system in general on the web, but precious little about fault diagnosis!

I suspect my fault is related to the ECU receiving incorrect sensor voltages. This could be down to a lot of reasons of course, not simply broken sensors! It's interesting how the wiring loom puts low voltage sensor wires, un shielded, next to the injector wires - with their 70V spikes.

DickieG · Post by **DickieG** » 29 Jun 2008, 07:38

Do you have the exact description/fault code number recorded when you had the codes read? I've looked through the Citroën diagnosis manual (genuine dealers one) and of all the codes that can be recorded there isn't one to match your description.

The manual does state that spontaneous acceleration can be caused by;
1, Mechanical fault, accelerator pedal cable.
2, Coolant thermistor function.
3, Running on oil due to vapour recycling : Fluid level.
4, Fuel pressure sensor function.
5, Mechanical fault : Fuel pressure regulator - high pressure fuel pump.

Have you found this link yet? http://www.christiantena.pwp.blueyonder ... index.html

rory_perrett · Post by **rory_perrett** » 12 Jul 2008, 14:09

Following the demise of my Xantia 2.1TD I have picked up a Xantia Hdi (110). Had a similar problem, the car seemed to be driving itself on occasions with the engine accelerating up to approx 2500rpm all by itself. In my case I think is was something to do with a sensor on the air intake. The connector to this is broken and not “locked” into position. Used a tie wrap to hold it place. I also degreased and pressure washed the engine and replaced the air filter with a Green washable sports filter. Problem seems to have gone away, just don’t know which one of the 3 things I did last weekend cured it.

No K light showing on mine, but as it never illuminates (assuming its got one) it might just not be working.

Rory

deian · Post by **deian** » 12 Jul 2008, 18:22

I guess I'm learning new things too, as we always do in life, especially about citroen cars (lol).

Oh well, out of the window goes my theory.

I would suggest any sensors then, hooking it up to an ECU reader will help of course.

nick · Post by **nick** » 12 Jul 2008, 18:49

rory_perrett wrote: In my case I think is was something to do with a sensor on the air intake. The connector to this is broken and not “locked” into position. Used a tie wrap to hold it place. I also degreased and pressure washed the engine and replaced the air filter with a Green washable sports filter. Problem seems to have gone away, just don’t know which one of the 3 things I did last weekend cured it.

No K light showing on mine, but as it never illuminates (assuming its got one) it might just not be working.

Rory

A fault with the MAF sensor as you describe doesn't seem to bring the 'K' light on on this Bosch system. With mine I tried unplugging the sensor with the engine running, the engine note on tickovever changed very noticeably with it unplugged but even that didn't bring the light on. It seems that in absence of sensible data from the MAF, the ECU defaults to using a best guess set of values to try to keep the engine running relatively normally.
I imagine an intermittant loss of signal caused by a dodgy connection to the sensor could confuse the ECU considerably though. There was also a known fault on early HDis with earthing problems to the MAF. The cure was to run an additional earth wire to it.