"Engine auto-diagnosis" light woes

[red_dwarfers]

<essential background story> Me and the family went on a run to do a spot of mackerel fishing yesterday in the Xantia </essential background story>

The coolant temp was heading towards 80-85 degrees, and just as we were getting to the end of the run the "Engine auto-diagnosis" light came on, which according to the handbook means that there is an ignition or fuel injection fault.

When the bulb firsts started doing its thing yesterday it would have a lot more 'on time' doing it's flickering under 2000 revs than if I accelerated over 2000 revs, when it would flicker but sort of go off before the bulb fully comes on, if you get my drift.

After giving it a nice 150mile round trip today i've come to the rough conclusion that when the car is pootling along at a steady speed the light just stays on most of the time. Generally speaking if I accelerate then the light will start flickering. Today's results are all very general and rough and there were many exceptions to this rule but its a start.

I've had a look back in the forum for this light and as far as I can see a couple of people have had it:
http://www.frenchcarforum.co.uk/forum/v ... odiagnosis
I would be tempted to say it could possibly be linked to Xac's problem last year but the car has only been running on 95-100% veggie for a month or so and the last two weeks has been filled up with diesel with probably about 20 ltrs of veggie still in the tank. And surely in this hot weather that shouldn't be the problem?


Some bits that probably arn't in the signiture that I really should add:
190k miles on the clock
Clutch on its way out...eeek!
Late '97 Mk1 Xantia

[CitroJim]

So did you catch any Mackerel? I adore eating fresh Mackerel caught straight from the sea, a real treat

The usual suspects for bringing on the Engine Management Light on a 1.9TD is either a duff Needle Lift sensor, a duff load sense pot or a duff TDC sensor although if any are really duff the car will run very roughly as the pump fail safes to very well retarded injection timing.

What the light is telling you in fact is that the ECU has not been able to set the timing value it so desires on the pump. It sets the timing by pulsing the timing servo on the pump and comparing the TDC sensor and Needle Lift Sensor signals to see if the timing has indeed been set to its chosen value it determines by looking up a map in the ECU based on engine RPM, engine load (from the load pot - how hard you have your foot down), road speed and coolant temperature. It measures the time difference in signals between the Needle Lift and TDC sensors and trims the timing in a feedback loop until it is correct. If it fails, it gives up, sets the timing fully retarded and shows you the light...

So, firstly, check and clean the connections to all sensors mentioned.

The running on veg is very unlikely to be the cause although as the timing servo is a hydraulic device that uses the fuel as the hydraulic oil, it could be if it was incredibly thick (unlikely in June) or if it was rather badly aireated. Air bubbles in the fuel could upset the operation of the timing servo. If all else fails, it is worth checking the usual suspects for air leaks (leakoff pipes, filter housing, priming bulb etc).

[Xaccers]

My money is on air in the fuel line
If I run my tank dry (ie it's sucking up air) I'll get the K light come on even though performance isn't affected noticably.

[red_dwarfers]

Im 100% sure that there is no air in the fuel line as there is a seethrough bit of pipe coming from the fuel filter with no bubbles.
Where do I find these three sensors to check?
I wouldn't say performance has been retarded much if at all.
I did play with a couple of connections on the IP yesterday, took one of them off and had the engine running, Cor! It sounded like a right old tractor!

Oh and Jim, unfortunatly we didn't catch any makerel in the 2 hours we were out, it seems that no one did that day. The day before though, the bloke said they were bringing them fine.
Hope that don't happen too often or it'll not do his business much good.

[Xaccers]

The needle lift sensor is on the second injector, the TDC sensor is on the top of the gearbox by the body of the engine, lightly to the back.
They've both (if memory serves) got BROWN connectors, just pop them apart and give the contacts a good clean.

[red_dwarfers]

Cheers Xac
While engine is running:
I disconnected the TDC sensor and there was no difference to anything.
While this was disconnected I also disconnected the needle lift - lost rev counter and engine went into tractor mode and K light still on.

Playing with wires when engine switched off then switching engine on:
Disconnected needle lift sensor and connected TDC - K light stays off, engine feels more responsive and powerful and runs better at lower revs. Still got rev counter and engine sounds smoother.

Can I presume that my needle lift sensor is dud?
Is the ECU being bypassed, hence the K light not flickering and going back to pure mechanical mode? I would have thought that the NL sensor needed to be connected for the timing to be corrected, but it seems a lot better without?

[CitroJim]

C
I disconnected the TDC sensor and there was no difference to anything.
While this was disconnected I also disconnected the needle lift - lost rev counter and engine went into tractor mode and K light still on.

Playing with wires when engine switched off then switching engine on:
Disconnected needle lift sensor and connected TDC - K light stays off, engine feels more responsive and powerful and runs better at lower revs. Still got rev counter and engine sounds smoother.

Short answer no, the Needle Lift Sensor appears good. The first paragraph above proves that. The second paragraph proves the TDC sensor is good.

A longer, more considered answer suggests that as the problem is intermittent, the Needle Lift Sensor could well be the cause as it operates in a rather hostile environment compared to the TDC sensor.

The Needle Lift Sensor is integral with the injector and the whole injector needs to be replaced. These injectors are expensive new but it might be worth searching one out in a breakers yard. If you do swap the injector, note that a special socket is required to undo it and the copper fire washer must be replaced. Also, strict clinical clenliness must be observed at all times when working in this area of an injection system due to the very fine tolerances and precision engineering in an injector. A bit of dirt can cause damage and/or very poor running.

*SAFETY* take care that you don't do the injector pipe union too tightly as it can distort the pipe fuerrle and cause leaks, likewise if not done tightly enough. Diesel at the injector unions is at extremely high pressure and if leaking, the jet of diesel can cut skin like a knife right to the bone. Such a cut can lead to severe health problems so do take care. Also, in some people, diesel spilt onto skin can cause contact dermatitis. Wear gloves.

[red_dwarfers]

Cheers for the quick reply Jim.
As the engine is running fine would there be any harm just leaving the needle lift sensor disconnected and wrapped up in insulation tape for the time being?

[CitroJim]

As the engine is running fine would there be any harm just leaving the needle lift sensor disconnected and wrapped up in insulation tape for the time being?

No, none at all as far as I can see. If it is running sweetly and continues to do so without it, that's a result. Beware though, it might not continue to run nicely forever like that and the Engine Management Light may come on one day. Still, all you'll need to do is reconnect the sensor.

One thing you may like to try is disconnecting the batter for an hour or so to make the ECU "forget" all it knows and then try again. Make sure you have the radio code though...