MK 4 1.9Tdi injection pump timing keeps going out.

[Tdi jetta 4 ever]

Hi guys. I am struggling with my injection pump timing for the past 3 months. It keeps moving to the retarded position. When i check the injection timing on vcds its way too much retarded that it doesnt even show on the graph. I then adjust it to a slightly advanced position then everything is okay again.
Symptoms is i struggle to start the car in the mornings and there is no low down torque. I struggle to get the car going at the stop streets. Obviously because of the retarded injection pump.
What i have found is that the sprocket moves at that 3 x 8mm bolts.
What i have done is i machined the surface on the sprocket where the bolts make contact. It had deep marks from tightening and loosening from all the adjustments. I also put new bolts from VW. I torque the bolts at 30NM. No difference. After about a week the injection timing is too much retarded again.
Any ideas what would cause this. ? Thanks in advance.

[Tdi jetta 4 ever]

Anyone ? Any ideas ?

[VAG Fan]

So the sprocket is slipping on the stump of the pump?

To prevent the slippage, I would worry more about the other side of the sprocket, in other words, the mating surface between the pump stub and the sprocket. That's where you need proper friction to prevent slippage.

I'm no mechanic, but I would suggest three options: [Edit: four, actually]
[Edit: added this first one to the list] 1) Check that the pump-facing face of the sprocket is still perfectly flat.
2) Thoroughly degrease the stub of the pump and the mating face of the sprocket.
3) Add flat steel washers under the bolt heads, so that their clamping force is more evenly distributed onto the sprocket. Use slightly longer bolts if needed.
4) Find some form of friction "gasket" to put between the pump and the sprocket. I've never tried this, but I read years ago that one can use a type of paper impregnated with diamond grit for this purpose. Apparently the diamond grit grabs both the working surfaces. Whether it works - I don't know.

[Tdi jetta 4 ever]

Thanks for your reply. Yes i checked al those things when i had the sprocket removed. The surfaces is perfectly flat. Nothing had changed there. My guess is that something in the pump is going bad. Causing it to have more resistance. I do have a spare injection pump. I am going to fit that one and see if it still does the same. Yes i also thought of flat washers and spring washers together but then i thought why would the setup run like this for 22 years without problems but now its a problem ? The new bolts and the machining of the surface where the bilts make contact should have cured the problem but nothing.

[VAG Fan]

Yes, when I read your post, one of my suspicions was also that the internal resistance of the pump is increasing. I doubt that it's mechanical resistance, because then it would break down or wear out in a few hours. So, is it hydraulic resistance, i.e. attempting to pump against a hydrolock? Not sure whether that's even possible...

Speaking of spare injection pump:
Mine is getting quite noisy (lots of fine rattles inside), but for now, is still working fine. Engine starts and idles perfectly, power is also good.
But one never knows...
Did you buy a spare one for scrap and have it overhauled? What sort of money is one looking at? Could you name some suppliers?

[Tdi jetta 4 ever]

Hi yes you are thinking like me. I also thought it could be something like mechanical resistance or high pressure problems causing resistance somehow.
I bought my spare pump from Prinsloo scrapyard at Vredefort. I think i paid something like R2000. But that was something like 3 years ago. No i am not going to recondition the pump. I am going to try it first and take it from there.

[VAG Fan]

Thanks for the feedback, Robin.
Is this the original pump on your AHF, and what's the mileage? Mine's done 340,000.
I used to fill up with budget Diesel (MBT brand) for a few years, but I think this may have hurt the pump. It started making a buzzing mechanical noise when it warmed up. When I returned to Shell Diesel, this noise mostly disappeared, but now, the rattles and little buzzes are starting to come back.

Installing a used pump and seeing how it goes, sounds like a sensible move (controlled gamble...)

I'm very interested how things turn out - if you have any new developments, please keep this thread posted.
And sorry I couldn't be of more help...

[Tdi jetta 4 ever]

No problem Mark. Yes its still the original pump the car came with. About 290000km on now. My plan is to start replacing the pump on Sunday. So i wil keep you and all others interested up to date.