XM 2.5 TD coughing & spluttering

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noz
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Joined: 05 Mar 2003, 03:33
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XM 2.5 TD coughing & spluttering

Post by noz »

Now that I've got it fixed, thought I might share a gem with you in case there are any more sufferers having the same symptoms.
To cut a very long story short I had a severe knocking noise started one day at the top end of the engine (diagnosed since as being a fauly injector and hence burn pattern). Took a long time to diagnose (trying to deny the obvious because it was too painful to consider) and it turned out to be a badly damaged piston. The knocking noise was VERY bad piston slap. I stripped the head off taking great care to mark the belt, sprockets and engine with paint before I started. I replaced the offending piston, new set of rings, new set of big ends, new belt, new gasket set, new injector nozzles. I marked the new belt with paint to match the old one and rebuilt the engine. I was always nervous about the belt/sprocket alignment because it just didn't feel right. However, I persevered and got the car back on the road.
The car, from that point onwards exhibited a very annoying trait. After warming up, when slowing down for traffic lights or a roundabout the car would falter and cough when trying to pick up speed. This happened every time I slowed down and in town was a real pain. I discovered I could cure it by getting some speed up and throttling back for 3 seconds and the problem went away until the next time I slowed down.
I measured every sensor and acuator and compared the results to the book - no joy. I bought an oscilloscope and traced both the needle sensor and the TDC sensor - no joy. I took it to 4 different garages and had it plugged ino the diagnostics - no joy. Thought seriously about a box of matches !
In parallel with that, after the rebuild, I had a bad oil leak between the head and the cam carrier. There's no gasket - you're supposed to use a liquid gasket. I used Hylamar but it failed. The thought of taking the carrier off again filled me with dread since the job is a real pain. It seems that half the engine bay needs to be dismantled just to get to the bit you need. Anyway, I plucked up the courage to do this last weekend. It wasn't as bad 2nd time around now that I new the sequence in which the parts had to be disassembled. Again I carefully marked the belt, sprokets and engine with paint. I used the proper gasket compound and refitted the cam carrier. Again when I tried to refit the belt it just didn't feel right, the marks lined up but the datums didn't. Eventually I plucked up the courage to ignore the paint marks and set up the belt using the datums. When properly fitted the cam shaft sproket and the injection pump sprocket were 0.5 and 1 tooth out respectively compared to the paint marks. I turned the engine over by hand 20-30 times just in case I had a valve/piston clash. I nervously started the engine and listened for the crash of metal. It sounded as sweet as a nut. The 'engine noise' had disappeared and it revved much more smoothly. I took it out for a test drive and it drove beautifully.
The stuttering problem has gone, the engine is a lot quiter and I increased my mpg by 5 to 36 - a roaring sucess. Many other small, insignificant symptoms also disappeared. (eg ocassional unsteady tickover). The car is a real joy to drive. I never would have considered a diesel before - now I wouldn't consider anything else.
My only conclusion was that the belt must have been fitted wrongly when I bought the car !
On the subject of belt tension mentioned in other posts I'll add my twopennyworth. I have worked on cars since I was 10 years old although I'm not a mechanic to trade, I'm a building services engineer. I have replaced countless belts in my time and never used a tensioning tool. The old rule of twisting the belt through a given angle depending on the distance between the two adjacent pulleys has always served me well and the XM is no exception. I appreciate that it's a subjective assessment and there's no substitute for experience but you mustn't believe the Haynes book of lies. Reading it would have you believe you'd have to buy half of Halfords to change a light bulb. A certain owner of a well known XM dealership spouts the same advice as Haynes. Not to be trusted in my book.
If anyone wants to change their belt or just wants to know the ins and outs of the job I'll gladly explain in detail. The clip holding the EGR pipe on to the exhaust is a real treat !!
cheers
noz
ps
great forum Jon, the problem with the Citroenian (although a great mag in its own right) is that it takes 2 months to have a conversation by correspondence. The benefit of the forum is that it's instant. Keep up the good work[8D]
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