Any Lucas Epic experts out there (Xantia 2.1 TD)??

Jonesy · Post by **Jonesy** » 28 Jun 2009, 09:39

My Xantia 2.1 TD has started doing some strange things on the throttle. It holds on to the revs for several seconds when you have released the pedal, which can be disconcerting to say the least. Now, I know these systems have a 'fly by wire' throttle to the pump and really have no idea how this works apart from there must be a cable going to a throttle position sensor somewhere under the bonnet. Also, and don't know if it's related but once whilst idling the engine started to 'hunt' with the revs going from 1400 to 1600 rpm and back every couple of seconds, this cleared after about 5 mins sat in traffic (almost seems like an air leak but pretty sure it isn't).
The car is still in great nick and superb mechanically so any help on this would be much appreciated, I don't want to scrap it! I know the Lucas Epic system was much maligned but I think a bit unfairly as the car has not missed a beat in 134,000 miles, returns 43 mpg average and is 11 years old!

Post by **CitroJim** » 28 Jun 2009, 09:56

There's two possibilities here, one extremely simple and the other not quite so.

Firstly, the throttle cable operates a throttle position sensor (effectively a potentiometer) under the airbox. It gives very little trouble.

The EPIC is VERY sensitive to air leaks anywhere in the fuel supply system and much more so than a Bosch or Lucas mechanical. The reason for this is that all the pump functions are controlled by hydraulic servos that use the diesel as the hydraulic medium; any air in the diesel and you'll have problems.

So, although you don't think it's air, I'll wager it is. Do all teh normal checks that are applicable to a Bosch looking for air leaks on the supply lines paying particular attention to the primer bulb and filter housing. Also replace all the leakoffs as the EPIC is extremely sensitive to leaky leakoffs.

The other possibility is that one of the ESOS electrovalves within the pump is beginning to fail although the classic symptom of this is that the engine runs on for a while after cutting the ignition. You've not reported this so hopefully, they're OK as to change them is a pump strip job although it is a task just on the bleeding edge of DIY feasability. The ESOS electrovalves are a little analagous to the stop solenoid in a normal pump but they also modulate to control fuel delivery and timing. They fail because the viton rubber tips on their valves begin to break up.

Strangely, a partially choked fuel filter can give some funny symtoms too.

Check very carefully for air leaks in all the usual places and that should resolve the issues. Be aware though that if an air leak is allowed to get really serious, it can cause the pump to loose control and result in an engine runaway.

Jonesy · Post by **Jonesy** » 28 Jun 2009, 21:31

Hi Jim,
Thanks for the info. and it's nice to have found an expert!
The engine does not run on at all when switched off, so I guess this is one good sign.
I will check over the car very carefully for leaks and replace the leak offs etc. I may also replace the fuel filter even though it's been replaced in the last 12,000 miles.
Once again thanks for the advice, I will check over tomorrow evening and let you know what, if anything I find.

Jonesy · Post by **Jonesy** » 13 Jul 2009, 22:05

I finally got round to doing all the usual checks for air leaks and really could find nothing amiss, the leak-offs are all in good nick with no signs of failure and all the rest of the pipework and primer bulb appears the same, BUT, I happened to notice that when I removed the fuel filler cap after the car had run that there was a whoosh of air! I took the car for a run for a few miles and filled the tank with diesel and again on removing the cap the same thing happened.
So I am hoping that there was a blockage in the fuel tank vent so I have removed the relevant pipes and blown air through them and although there did not seem to be any blockage I now don't get the whoosh of air when the cap is removed.
I am sincerely hoping that this has cured the problem, we have done about 40 miles so far and it has run absolutely fine, so fingers crossed.
One thing I don't quite understand and hopefully Jim can point me in the right direction is how this made the car run as it did?
Is it just a case that effectively the diesel/air ratio is incorrect and so making the engine in effect run leaner and hence it wants to rev more freely???
This could be purely coincidental as it did not always do it but I am hoping it is/was related.
Thanks for your help.

One thing I forgot to mention and I believe may be related is that the car ran fine for the first five to ten minutes which would be accountable to a build up of the vacuum inside the tank?!

lolingram · Post by **lolingram** » 14 Jul 2009, 08:03

Check very carefully for air leaks in all the usual places and that should resolve the issues. Be aware though that if an air leak is allowed to get really serious, it can cause the pump to loose control and result in an engine runaway.
_________________
Jim

I can attest to this... happened to me twice before I very reluctantly dumped my J reg XM estate. Be prepaerd to stuffe the car into 5th and just drop the clutch. Only effective way to save the engive from exploding.

KP · Post by KP » 14 Jul 2009, 08:06

I would say it would be because the intank pump and the high pressure pump either had to work harder to get the correct injector opening pressures or that the pumps were not pushing out the right pressures to start with in which case a fault might be logged in your ECU but then a lexia would only show this up if the engine management light is not constantly on...

Jim will no doubt be able to give the professional judgement on this as mine is just my own theory

Post by **Peter.N.** » 14 Jul 2009, 12:14

As Jim said, the pump is very sensitive to fuel pressure, the vacuum caused by the air vent obstruction would lower the pressure within the pump and also make it far more prone to air being drawn in somewhere.

The vent blockage problem is relativly rare now but it has cropped up several times recently. In the days when lift pumps were fitted it didn't affect the engine so much as collapsed the fuel tank!

Jonesy · Post by **Jonesy** » 15 Jul 2009, 11:23

Unfortunately it does seem like it was coincidental as it is still doing it! Damn.
I will have to have a closer look for leaks and just hope that it is not a problem with the injector pump itself.
With it being intermittent and not happening when the engine is cold, it makes things more difficult, so any further advice on what else to check would be appreciated.

Post by **Peter.N.** » 15 Jul 2009, 12:05

The only 100% way to check for air is to fit a length of clear plastic pipe in the fuel system as near to the pump inlet as possible - either you will see bubbles - or not, but it least it should confirm the diagnosis.

hobblerian · Post by **hobblerian** » 17 Jul 2009, 22:04

Glad I found this thread, my Epic 2.1td XM is suffering from exactly the same symtoms, luckily they had the foresight to fit almost clear fuel lines in the engine bay. Tiny tiny air bubbles can be seen coming from the tank lines, I suspect it could be the sender unit in the fuel tank as I had a similar problem with my S1 2.1td XM. The air caused starting problems in the end with that car as the bosch pump on that could cope the air bubbles better.

The cure for my S1 was a new sender unit and replacement fuel line from tank, as soon as I've recovered from my up coming operation I will be looking to see if the current problem can be put down to a leaky fuel line union around the tank area.

Old-Guy · Post by **Old-Guy** » 18 Jul 2009, 12:38

Jonesy

To clear up a common misunderstanding: Apart from being 'compression ignition' engines, the fundamental difference between diesel engines and petrol engines is that diesels do not operate on a fuel/air mixture - there is no such thing as lean/weak, correct or rich mixture.

Diesel fuel is injected as a fine mist into the cylinder just before TDC. The compressed air is so hot that the diesel ignites instantly. Power output is controlled by adjusting the amount of fuel injected, air flow is unrestricted (not 'throttled' by a valve as the mixture is in a petrol engine) so a constant volume of air is inducted each cycle.

So for a diesel vehicle, it's really nonsense to talk of the 'ignition' switch and the 'throttle' pedal. The former switches on the fuel injection system, while the latter is really the 'power' pedal.

For a diesel to run cleanly, the proportion of fuel to air has to be considerably lower than in a petrol engine. Black smoke from a diesel is sign of unburnt fuel - restricted air inlet, poor (injected droplet size too large) or mistimed injection.

Turbo-chargers use waste energy in the exhaust to increase the pressure of the inducted air. An inter-cooler is an air-to-air radiator to cool the compressed air so that it's density is greater.

The glow plugs in many diesel engine designs pre-heat the combustion air for easier (cold) starting because the mass of cold metal combined with slow cranking speed means that the compressed air at the end of the compression stroke wouldn't otherwise be hot enough to ignite the injected fuel.

Hope this helps you understand a bit more about your engine and its erratic behaviour.

Guy

Jonesy · Post by **Jonesy** » 18 Jul 2009, 21:09

Hi Guy,

I fully understand and appreciate all of what you are saying, but are you saying that it could not be air in the fuel that is causing this odd running behaviour? What I was trying to say (and did not make myself clear) is that could air present in the fuel in effect make the engine run faster with the same 'throttle' position or is this purely down to the ecu getting confused or as has been mentioned before a problem with the Epic pump!
When I had an air leak in my old XUD BX because of an ingress of air on the pre-heater all that happened was that the engine felt lumpy and felt as though it was mis-firing which I know you are probably going to say is not possible, mis-firing!! Araldite around the union fixed this for 2 years, if only it were that simple this time.
Thanks

fred1 · Post by **fred1** » 18 Jul 2009, 22:06

Hi,

Experienced something similar with a an Escort 1.8D.

Engine revs would suddenly rise and fall by 1000 or so when at idle or would hold high when throttle released.

Turned out to be the non return valve in the primer pump head of the Lucas fuel filter.

This was leaking back to the tank causing the injector pump to see it as a weak fuel supply and increase supply to engine.

New primer pump head fixed it.

On the Escort the fuel filter/primer pump was mounted on the engine (unlike the same unit on the BX) and the extra vibration caused the non return valve seats to wear and the problem returned every 40-45k regular as clock work !

Was a well known problem on the Escort, a Lucas diesel mechanic put me on to the solution when I was enquiring about a the cost of a new injector pump. New filter hear was about 1/20 of the price !!!

Regards

John

Post by **CitroJim** » 18 Jul 2009, 22:22

No, the difference with the EPIC is that it uses hydraulic servos to control timing and fuel delivery under ECU control. The hydraulic fluid in the case of the EPIC is the diesel fuel itself. Now if that hydraulic fluid contains air, the operation of the servos will be upset and erratic and this is why the engine appears to speed up and do other odd things.

"Misfiring" in a diesel will be the result of interruptions to fuel delivery to the engine. Again usually as a result of air but giving different symptoms.

Jonesy · Post by **Jonesy** » 19 Jul 2009, 21:36

Finally got round to replacing all the leak-offs and blanking plug this afternoon on Jims recommendation. Appeared to be nothing wrong but had gone very hard (11 years old).
Also replaced the fuel filter and did not like the look of the old one even though it had been in less than 2 years, not blocked but looked rather unhealthy.
Took the car for a spin for about 15 miles and it run fine, but then again it would do that before, we'll see.