Mysterious air leaks?

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freek
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Mysterious air leaks?

Post by freek »

Goodevening!
I have become quite familiar with air leaks in the fuel system of my BX trd turbo. In the past I replaced the valves in the (bosch) filter housing as well as the priming pump membrane and all the rubber seals. As a precaution I replaced recently the leak off pipes (the fuel pump is a Lucas/rotodiesel). Last year I did not experience any trouble. But since a week or so the idle speed suddely increased now and then. And yesterday morning the engine did not start at all. After priming I succeeded finally but the idle speed was very unstable. I checked the filter housing again as well as the leak off pipes but there are no obvious faults. And this morning the hand pump was still hard which I think is a indication that there are no leaks in the filtersystem. But even so the engine was again very hard to start and now the idle speed during a test ride did not fall below 1800 rpm. I am quite puzzled! What can be wrong? By the way: the stop solenoid is working ok. So now I am at a point that the pump is a verdict. Are there any weak spots in the Lucas/rotodiesel pump which I can check? Or did I overlook something else? Has anyone experienced a similar problem? Your hints are welcome! Regards, Freek
oilyspanner
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Post by oilyspanner »

Blocked fuel filter? check filter for water as this can cause engine to race and mess about.
Stewart
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fastandfurryous
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Post by fastandfurryous »

Another point to check on these is the fuel pre-heater built onto the water pump inlet (hidden way down the back of the engine) It is made of sintered aluminium, which often goes porus. I've had this happen on 2 1769TD engines (in 405's). The fix is to bypass it, or even take the feed pipe to it, and re-route it straight to the fuel filter. Getting to it is a major nightmare though.... sorry!
freek
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Post by freek »

Thank you for the quick hints. But unfortunately the filter is 2 months old and the pre-heater is by passed a few years ago. So these cannot be the cause....
freek
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Post by freek »

I was thinking something else: is it possible that there is something wrong with the tank outlet so that it sucks air with the diesel in the tank? The turbodiesel has 2 tanks; a small and a bigger one. I remember that a few years ago it occurred that after driving through a bend in the highway with a considerable speed the the engine speed also fluctuated for a few seconds. This mystery disappeared however after a year or so.
citronut
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Post by citronut »

is the cold start unit going up the spout,or perhaps check inter cooler to manifold D shaped seal,also even if you had not bypast fuel heater which on BXS is a cigar shaped unit on bulkhead behind cam belt cover,and it was letting in air your primer would not be firm half an hour later let aloan next day regards malcolm
NiSk
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Post by NiSk »

Read what Zeljko Nastasic has to say about the Lucas/rotodiesel pump at:
http://www.tramontana.co.hu/citroen/engine/diesel.html
and then worry yourself to death (or fix an new pump from a scrappy - but check the milage!)
//NiSk
freek
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Post by freek »

I know that the construction of the CAV/rotodiesel is less than perfect and subject to wear. But I can hardly beleave that this can cause a 'sudden death'. You should expect a period of deterioration in the beginning and this is not the case.
jeremy
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Post by jeremy »

It would actually seem that the problems have arisen since the filter was changed!
Starting could be glowplugs - they will start on 2 without too much difficulty! there is also the 'waxstat' operated advance device that should give a fast idle. When mine failed the thing would hunt furiously when cold.
The fact it revs to 1800 rpm suggests air in the pump. I asume you don't run it with the fuel light on? I've always wondered if the last couple of gallons were really useable if the suspension was allowed to sink and the fuel ran back into the back tank! Having said that I've never had any trouble but never run it for more than a few miles with the light flashing. It is always parked on the level at home - I don't know what would happen if I parked it nose up with an empty tank.
I expect you have already replaced the pump feed pipe with clear so that you can see if there are any bubbles. If you have its worth making sure that this pipe hasn't hardened and is leaking!
leakoff's dont make any difference with Roto-diesel pumps (have had one split twice on the ZX and it just smelt and dropped fuel!)
Jeremy
citronut
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Post by citronut »

air in fuel system usuly makes engine run lumpy,on petrol injection cars to much air in induction makes them run to fast, have you checked throtle lever on pump to see if it is tight or binding,or have you adjusted cable free play,make sure throtle lever is at its stop when car is ideling,also check cold running lever is right of when hot regards malcolm
freek
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Post by freek »

Hello again,
The mytery continues, but now in a positive way! As I wrote yesterday the engine idle speed was app. 1800 rpm when warm. I parked the car in that state in the garage. Today I dared again to try it. The priming pump was still hard, so I assumed that air didn't enter the system. I turned the key and the engine started after app 5 sec (normally it starts instantly). But the idle speed was constant at 1000 rpm as usual. So I decided to go for a test drive and to my surprise the engine reacted normally and after a few minutes the idle speed was normal at 800 rpm and stable! In short: no problem what so ever... My conclusion is that yesterday still air was trapped in the fuel pump and didn't get out. Today apperently it did at first. What I have forgotten in the whole story is that the only cause of air I could imagine was a tiny spot of corrosion in the aluminium filter housing. This spot was also at the outside of the housing so I assumed that the housing was porous at that spot. I have put some two component glue on it. But when I didn't notice any difference yesterday I decided not to mention it. But after all this could have been the beginning of the problems. I didn't suspect the filter because that was changed in march just before a trip to Austria which was without any problem. The cold start device operated as supposed. When this is the end of the story the conclusion is that air can be very troublesome to get out! I am very curious what will happen tomorrow...
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