Xantia's sudden loss of Power -- Help

AndersDK · Post by **AndersDK** » 28 Apr 2007, 20:43

I'd say always check simple things first.

On a diesel this always means the fuel feed to the pump. Inherent by the function, any diesel pump will get its fuel volume regulation totally screwed up by air on the fuel inlet side. This makes the engine run very bad and will make it soot or smoke.
This is because at some injection cycles it runs OK, some injection cycles it runs lean and some injection cycles it runs rich etc. etc - in a completely random pattern. The engine rpm's can not shift as fast as the fuelling shifts, hence the lumpy and smoking running.

First point to check is the last fuel hose from filter to pump. This hose must be replaced to a clear PVC type such that ANY - however small - air bubbles are readily seen. If any air - any at all ! - is seen in this test, you have a leak problem in the fuel filter and/or backwards in the fuel linings to the fuel tank.

This is also the only thing I could think of that would suddenly and abruptly fail driving over a speed bump.
Plus the fact that airleaks are by far the most common problems that screw up otherwise good running diesels.

tomthered · Post by **tomthered** » 14 May 2007, 09:34

right guys especially AndersDK and Peter.N

Got back from Cyprus last night, gorgeous weather but crap in UK!

Went round and picked car up. It sems that he had to reset the timing belt which apparently runs the pump as well as others. It was 45 degrees out and he said he had never come across this before. It starts fine, although slightl hesitations now and again whilst cold. Once hot no problems.

He did say that the car was spewing a tiny bit of blue smoke (oil he said) when cold but seemed OK when hot. Took it for a drive and it seemed fine. Not tried starting it yet (monday morning) but would probably be OK. He said the engine may be on the way out and to get rid now and get another.

Does anyone know why the timing belt would suddenly jump like that? As well it does not seem to burn much oil, although with 132K on clock I would expect some loss, but nothing major.

Any suggestions guys on what I should do next? I asked about replacing fuel pump but he said not necessary as running fine now. Says it took him ages to figure out what needed doing but removed the guards? and make it easier to get at next time if there is one!!!!

What could make it burn a little oil at start up, run a little lumpy, ie engine tickover lump on tickover, but fine when hot?

jeremy · Post by **jeremy** » 14 May 2007, 11:33

I get worried by anyone who leaves guards off 'as it'll save time next time' They're there for a purpose - one of which is to stop your clothing dragging you into contact with moving parts. He clearly hasn't considered this risk (and it might be his clothing) - so what else has he not considered.

AndersDK · Post by **AndersDK** » 15 May 2007, 00:29

45 degrees out on the timing belt

How would the timing belt slip 45 degrees on the pump

If that really is the case, I'd certainly had done at least 2 things :
1) removed both idler, tensioner and waterpump for inspection and possible replacement.
2) replaced the timing belt, no questions asked, as a precaution

Also I'd possibly dig into the diesel pump timing belt cog - looking if it really was a rigid connection to the pump axle. As this sounds to me as a very good reason for the problem first off.
I really do have a suspecious mind on the pump axle and belt cog. The belt wont just slip 45 degrees on the pump cog - and survive that

About the remaining problems : pretty sure most of it is a fine adjustment of the diesel pump. This is VERY sensitive. Nothing like you know from a petrol engine.
The rest may well be air problems on the suction side of the pump.

A diesel engine is a very solid constructon in general, as it has to withstand the pretty high compression ratio of approx 25:1 with resultant large vibrations. This is close to 3 times a petrol engine.
132K on a well-looked-after diesel engine is nothing close to end of service life. You should have at least the same mileage left on that engine.

tomthered · Post by **tomthered** » 16 May 2007, 08:10

Right as the guard is off I can see a bloody big cog wheel attached to the pump underbelly with a big nut on the end. I assume he would have checked this as I can also see the timin belt (I think). AndersDK are you saying that the cause may now be air in the line or a slight retardation of the pump injecting fuel at the correct time. If that was so why does it run fine at normal engine temp?

Why would the belt not survive slipping 45 degrees on the pump cog?

Do you think I should get rid or see if something else is amiss. I would rather not be left with egg on my face if its a serious problem!

Any other suggestions you or anyone can think of?

cheers Tom

AndersDK · Post by **AndersDK** » 16 May 2007, 23:08

Once hot no problems. I overlooked that.
You are right - its not likely to be an air problem then.

Could still be a minor timing issue. There is a coldstart circuit which exactly alters the timing at cold engine to prevent engine from stalling at coldstart instability. Also the idle revs are increased a bit - to some 1050-1100 rpm - for the same reason.

The cambelt would not slip untouched over the pumpcog teeth. It would be more or less stripped then. Either that or the belt tension must have been that loose it made the engine a ticking bomb to your repair budget !

I'd say check the belt tension once more, have the pump timing fine tuned and then enjoy the car.

tomthered · Post by **tomthered** » 17 May 2007, 12:18

I noticed on start that it seems to be running slightly fast (as my rev counter dont work due to some thing on the flywheel I have been told) is there some electrical circuit I should replace?

How can the pump be fine tuned, is there an instrument to do that or is it guess work? On a petrol engine you can connect it to an instrument that will show if its tuned correctly. Can you do the same on a diesel engine?

cheers for the help Tom

Post by **CitroJim** » 17 May 2007, 12:54

tomthered wrote:I noticed on start that it seems to be running slightly fast (as my rev counter dont work due to some thing on the flywheel I have been told) is there some electrical circuit I should replace?

This is correct Tom. When cold, the waxstat pulls the idle speed up slightly. There is also a small electrical circuit to give the pump some cold start advance. This works from a signal supplied from the glowplug controller and from a signal from a Coolant Temperature Sensor (the green one IIRC). The cold avance stays in effect until the coolant reaches 60 degrees. The signal operates a small solenoid on the front side of the pump. Try disconnecting the electrical connection to it when the engine is cold and you will hear a slight but distinct change in engine note as it is connected and disconnected.

tomthered wrote: How can the pump be fine tuned, is there an instrument to do that or is it guess work? On a petrol engine you can connect it to an instrument that will show if its tuned correctly. Can you do the same on a diesel engine?

cheers for the help Tom

Setting timing on a mechanical injection pump is a very critical job. It must be set very precisely and requires the use of a Dial Gauge (DTI) and a special adapter. Very small timing errors can make a tremendous difference to performance and economy. This is a job best entrusted to a specialist simply because of the equipment needed although the BoL covers it adequately if you want to have a go. The problem is in obtaining the necessary DTI adaptor unless you can make one yourself.

Some can indeed set timing by ear but it's hit or miss and you need a great deal of experience to do so. I'd not try it.