VW Polo alarming diesel knock - frjim
Hi,
I've a real puzzler with my 1998 Polo diesel. It has a 1.9D AEF engine with a Lucas mechanical pump with accelerator cable that has now covered 105k miles. The starting symptoms which are rapidly getting worse are:- when the engine turns over there is an alarming knocking sound and the whole engine rocks violently. This only occurred when the engine was hot but now does it also when cold. It used to start after 1 or 2 seconds but now takes a couple of 5-6 secs + fully depressed accelerator, I've put new heater coils in, new timing belt and tensioner, checked the timing multiple times also tried with advanced and retarded levels, checked fuel supply to injectors, tested cylinder compression which are Nos1 - 20bar nos2 - 23bar nos3 - 21bar nos4 - 17bar. Thing is when it does go it sounds fine, pulls well and there is neither strange noises nor smoke (black, white or blue). + if on starting the stop lever, found on the top of the pump, is activated then without fuel supply the engine turns as it should without the alarming knocking sounds. I would be grateful for any help with this. Cheers Jim.
VW Polo alarming diesel knock - Peter D
I'm no deisel expert and I am sure there will be one along shortly but your 17 bar pot is really on the edge of not igniting deisel oil. If this is the case does she not smoke a lot when she does fire on all four due to the excess fuelling. Regards Peter
VW Polo alarming diesel knock - frjim
Hi Peter,
Thanks for replying. This is the really strange thing that when she does start, there is no smoke that I can see and that she runs fine, pulls fine and there are no strange noises. Do you know the bar pressures in diesel engines?
Regards Jim.
VW Polo alarming diesel knock - Number_Cruncher
If this were my car, I would first take the injectors out and get their spray patterns and opening pressures tested - it shouldn't cost much. I'd be particularly suspicious of the injector in the cylinder with poor compressions - has it been spraying all its fuel straight onto the wall of the cylinder?

Number_Cruncher

VW Polo alarming diesel knock - jc2
Instead of just having the pressures and spray pattern checked,have them serviced at the same time.They are then stripped,cleaned and re-assembled and then the spray pattern and pressures are checked-it doesn't take much longer and is well worth it;alternatively ask about a set of exchange injectors.Your knock could well be no. 4 trying to fire up.
VW Polo alarming diesel knock - frjim
Hi jc2,
Thanks for your advice. Others have talked of the problem being a)- fuel related b)- pump delivery problem c)- injectctors. What I have a problem with is that there is no smoke that I can see after she fires up! If there was excess / unburt fuel surely this would manifest itself as smoke. Then she runs fine.
Regards Jim.
VW Polo alarming diesel knock - frjim
Hi Nos - Crunher,
Thanks for your advice. I could kick myself as I've just had the pressures tested on Friday but asked to keep things to a minimum and hence nothing else was checked! Are you aware if the adative you put into diesel, to supposedly clean the fuel system and injectors might help?
Regards Jim.
VW Polo alarming diesel knock - nortones2
Suggest you have a look at this: tdiclub.com/TDIFAQ/TDiFAQ-8.html#b2

A number of fairly simple things to check.
VW Polo alarming diesel knock - frjim
Thanks for that tip - will have a look.
Regards Jim.
VW Polo alarming diesel knock - Number_Cruncher
When you say you have had the pressures tested, do you mean the cylinder compression pressures, or the injector opening pressures?

I would expect (if these are the types of injector that I think they are) that if you find a low opening pressure or a poor spray pattern, you are more likely to effect a good repair by replacing the nozzles than just by cleaning. If this type of injector doesn't shut properly, the needle/nozzle soon overheats, and is never right again, even after cleaning. But, all that is only true *if* you find a misbehaving injector.



Number_Cruncher
VW Polo alarming diesel knock - frjim
Hi Number Cruncher, The pressures I had tested were the cylinder pressures and not the injectors which I now wish I had done.
Re the injectors can you give me an idea of shape or style that I can look for.
Thanks -Jim
 

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