2007 S-line tdi - vcds shows injection start 6.5 degrees btdc??............hard starting...

[sparkymarky]

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[sparkymarky]

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[Rory Allan]

Hi Sparky My first post too, so go gently.

I have just done my 1.9TDi 2008 Caddy engine's timing checks and torsion value, as it seemed a bit 'flat' at low rpm . I found that the torsion value did in fact make a huge difference, as my van 'hunted' around in idling at anything over + 2 or under -1.5. I tried a few shifts of the cam and found a much better response at +1.5 KW (turbo kicks in around 1700rpm now, 2000 before, and there is much better 'grunt'. I have to still see what the fuel economy is like).

A diesel needs to have the timing set a bit before TDC, as you don't want the start of your squirt happening when the piston is at its peak. There is a bit of a lag between when the squirt starts and when the full explosion occurs (this should be at TDC). Your duration therefore looks spot on as the end of your squirt occurs pretty much bang on TDC.

Now the 'start of injection' is when the ECU opens the solenoid to allow the fuel in. But the squirt pressure is obtained mechanically via the camshaft lobes. So retarding the peak pressure attained by the injector pump by 2.9 degrees (your 'torsion value' - PS, negative means retarded) seems out of whack with the rest of the timing.

I would take it round to +0.5 or +1.0, or even try +1.5 , which will basically bring your peak squirt pressure forward by 4 deg from where it is now, and into a much healthier relationship with the opening of the gate (the solenoid) (You might have a situation where you're still squirting but half of it it is slamming into the closed solenoid (could be why the idling fuel cons is so low)

A negative torsion means you've retarded the timing (made it later) and advanced (positive torsion) means your peak pressure will be before top dead centre.

This guide is pretty good. How to adjust rough idle and camshaft timing on VW and Audi TDI pumpe duse engine

Clockwise with the 18mm bolt(which will move the cam clockwise and advance the injectors) to give about a millimetre's movement on the sprocket will probably end up at about +1 torsion (Yep, I had so many goes at getting mine exactly to 1.5, I have a good feel for it now). Its pretty easy to do so don't panic. You obvios;y have VCDS so try a few values and see what happens, but definitely don't go above 2 or below -2, as mine started idling really badly in these regions. PS, the limits are +- 3 deg. Go past these and VCDS will read 0, so keep an eye on the movement and take vsual markers of where you are. I find that the timing tabs on the cam timing wheel make good points of ref, as when you turn the bolt, these move but the sprcoket stays still (held by the cambelt)

I am suspicious that 6.5 deg BTDC may be a bit early for an injection start, as its usually around 1.5 to 2 degrees, but on an S-Line, it might need to be that bit earlier to get the full power.

Give it a go. You can't break anything and once you've got the cambelt cover off, its quite easy to make the adjustments.

This is also a great little doc

VW_TDI_with_PumpeDuse(2).pdf

Rory

[sparkymarky]

wow thanks for the long reply rory! I've moved the pump on my old 306 diesel before to get the injector pump timing spot on-that was a case of loosen the bolt push the whole pump forward or backward until you heard the engine note change and at the first bit of diesel knock, just retard it a mm. That worked spot on. Will do the same here but only adjust it a mm like you say and with vcds on the wing next to me i think until it gets nearer to 0-1. Will haev a go this weekend if its fine and report back....you're sure i cant do any damage? i know diesels these days are generating some serious fuel pressures.........

[sparkymarky]

I've just read the guide and it seems straightfoward.....but i think the 2.0 tdi is a twin cam.......i havent taken the cover off yet though but assume there are two cam pulleys???? in the guide there is one.......how will i know which one to adjust???

[Rory Allan]

I believe you still only have 4 injectors, which run off the front camshaft. So just doing the front one will work (you might want to check this yourself). I guess that ultra-theoretically, you should move the back one by the exact same amount (and you aren't going to get that right with the tiny movements we've talked about !), but literally you are talking a few hair widths of adjustment, and its not going to make much difference to the valve timing (which is all the back one does) as these have nice smooth cam lobes (unlike the injector pump lobes which are steep as anything to give you that rapid squirt).

I know in the petrol twincams the two camshafts are linked internally by a chain but can't find a decent piccie of the TDi twincam.

I'm going to leave it up to you. I don't want to give any false info. There are loads of forums on camshaft timing, and pretty much they all say the same, that most people with big negative torsions are having problems. Try a search for vw or audi camshaft timing or torsion value.

If it was me I'd have a go at the front one, and this seems to be supported by others (see first link). You have VCDS so you can always put it back exactly where it is if it doesn't improve things. Here are a few links to read from similar posts

Increased consumption VW MKV Golf - 2.0 TDI 16V BKD - TDIClub Forums

TDI Cam Timing Adjustment (for rough idle) How-to (with pics) - TDIClub Forums

[Rory Allan]

Been doing some more playing with VCDS and have noticed my ignition timing when cold is also way down at -5 ish, then when the engine warms up it gets pretty much to 0 deg at idle. When I rev it the timing changes to earlier and earlier BTDC (neg values) (makes sense, when its cold you need the extra time for the burn to kick in to overcome heat loss in a cold engine, and the same when its revving to compensate for the shorter burn window) So your injector should open around 0 deg (ignition timing) once warm at idle, so check this on VCDS, as the ECU adjusts this off the crankshaft sensor for TDC (you can't really adjust it and it shouldn't be out unless the belt has slipped a tooth). The torsion value can be adjusted (the mechanical pump timing of the fuel injector/pump, and earlier (advanced, +ve values) is better for the same reasons and all the reasons already discussed, at anything above idle revs)

[sparkymarky]

Been doing some more playing with VCDS and have noticed my ignition timing when cold is also way down at -5 ish, then when the engine warms up it gets pretty much to 0 deg at idle. When I rev it the timing changes to earlier and earlier BTDC (neg values) (makes sense, when its cold you need the extra time for the burn to kick in to overcome heat loss in a cold engine, and the same when its revving to compensate for the shorter burn window) So your injector should open around 0 deg (ignition timing) once warm at idle, so check this on VCDS, as the ECU adjusts this off the crankshaft sensor for TDC (you can't really adjust it and it shouldn't be out unless the belt has slipped a tooth). The torsion value can be adjusted (the mechanical pump timing of the fuel injector/pump, and earlier (advanced, +ve values) is better for the same reasons and all the reasons already discussed, at anything above idle revs)

Thanks for another post Rory you mention the front cam is the one I need to adjust ....of course my engine isounyed longitudinally being the a4......I'll have to check out your links and rotate the engine in my head to figure out if its the right or left cam to adjust in my case will have a go this weekend though me thinks!

[sparkymarky]

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