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Discussion Starter #1
While there are countless threads discussing the setting of the Torsion Value on PD engines, I have yet to find a good technical description of why it even needs to be messed with (versus zeroing it) and why it is a thing at all. Granted, I mainly come from the world of engines with timing CHAINS which have their own quirks, but basically if everything is locked to TDC, there's no mystery. Even every engine I have encountered with a belt-driven valvetrain is about the same, with one simply aligning timing marks. Yes, the PD engines differ in that the cam also drives the high pressure injector pumps, but it is well accepted that the Torsion Value tweaking has zero to do with the fuel injection, and it is all about timing of the valves.

So, why exactly is it that every PD engine shipped from the factory with varying torsion values scribbled onto the label on the belt cover? If VW had thought it best to set it to zero in all cases, I assume that they would have since that is basically what every other car maker seems to do. For instance, mine has "-1|62" written on it, with the bar not being quite that tall, but pretty long for a comma. I presume that it means that the cam was retarded 1.62° from the factory. At this point, the car has had 2 belt changes, as well as a new cam and lifters, so I wonder what the best value is now. The previous owner had just changed all of that before I bought it from him, and I have only had it for about 6 months. This gets to why I am posting this at all. The torsion value in VCDS reads -5.5° at idle, which is pretty far off of zero, but not out of the (wide) range of values that people in various forums have set it to and claimed improvements in power or fuel economy. Anyway, should I just set it back to the original value of 1.62°? The car smokes a little at startup, feels like it runs out of juice above 3000RPM and only gets ~39.5MPG (measured from odometer and gallons pumped when filling) when I did a few hundred miles on the highway with cruise control locked to 65MPH. Around town it gets 32-34MPG, and I feel like this is a little low. The car is a 2006 Jetta with DSG and 209K miles.

So, if anyone has thoughts on my explicit case above, I am all ears. Beyond that, I'd like to see if anyone knows the true technical basis for the big variance in torsion values that these cars shipped with. From a manufacturing standpoint, the pistons, rings, camshafts and valves are all going to be within a couple of thousandths or better as they come off the manufacturing line, so I do not see any way that variance in those bits would be the reason. The timing belt seems like the only item that could have anywhere near the kind of variability that might lead to each car having a unique torsion value optimum. Some may be a little stretchier than others, or have different thermal expansion characteristics, different tooth wear-in etc. Other vehicles with belts don't seem to worry about it, and I cannot imagine that the belt in our cars is super special, except for the additional tension in it from driving valves AND injector pumps. Other than my guessing, has anything ever been published that goes into detail about why torsion value (which I am calling "valve timing" in my mind) needs to be adjusted, and how one is supposed to determine the optimal value for their engine? Did VW get a dial indicator on a lifter and set the cam to a specific position at TDC (or some other angle) when they built these things? That's about the only way that I can think of that they would have been able to set the cam timing to an optimal value fast enough to be in a mass production environment.

Thanks folks! With any luck, maybe we can put this one to rest for good.
 

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This is a new forum layout with loads of bugs which have been reported in the new thread. There is no TDI Wiki at the moment.

You need to get your motor scanned (preferably with VAG-COM\VCDS) for any error codes logged in the ecu and post them, that will save a lot of guessing and check systems out.
 

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Discussion Starter #3
OK, success! I got out there and made the adjustments, and while I have no idea what it will do with fuel economy, the car actually runs WELL now. It was pretty gutless before, which I just attributed to it being a ~100HP engine and me being used to a ~200HP 2600lb E30 BMW. The TDI is not "fast" now, but I think that I an actually merge in the way that I usually like to without needing a 300ft runway. Overall it is a lot more pleasant to drive, and it starts a lot faster too.

Here's how I approached it this afternoon. First, I drove it around to get it fully heated up. After getting the boost pipe and belt cover out, I noted that the cam was retarded in the slots at almost the maximum possible amount.




Looking in VCDS, the torsion value was stuck at zero until the engine was warmed up, at which point it read -5.9 at idle and -6.4 when driving. So basically, it on or a little past the range where it could be measured at all.




So, given that it was a good 6~7 degrees retarded, and the cam:crank speed ratio is 1:2, I figured I would need to advance the cam at least 3 degrees (which is 6 degrees on the crank, and I assume torsion value is measured in crank degrees). I have a nice digital level/protractor, so I held it to the wrench and zero'ed it to start.




I then advanced the camshaft ~3 degrees, which got the three 13mm bolt heads nearly centered in their slots.






Back in VCDS, things were improved, but still a bit retarded relative to where I think they needed to be. Still, the digital level really helped to ensure that I didn't grossly overshoot. 3 degrees is not a lot, as far as your eye and a breaker bar are concerned.




Thereafter, I advanced it another degree, which got me slightly past where I thought I wanted to be (0.5 is indicated on the belt cover).






I made a final tweak of ~0.25 degrees in the other direction with the level, and that got me right where I wanted to be. It was reading 0.5 at idle, and 0.0 when driving. I probably missed it somewhere, but is the torsion value on the belt cover supposed to be the value at idle, or some other operating condition?




From there, I put everything back together and drove around for 15 minutes. The difference in response and power was very noticeable, and while I hope that fuel economy will improve, the car is vastly more pleasant to drive. I'll just have to see how my economy calculations look over the next couple of tanks of fuel. Anyway, after the drive I re-checked the idle values and they seemed to hold, so I considered this little project done for the day.




My idle fuel consumption went up a little versus before, but most info I have read indicates that minimizing idle fuel use does not translate into minimizing driving fuel use. We'll see. How do my Injection Quantity Deviation values look?
 

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Discussion Starter #4
Oh, and lastly how do my EGR and boost values look? I logged them while driving, and here is what things looked like with a mix of WOT, deceleration and cruising. It seems like the EGR & MAF actual values are considerably higher than the EGR spec value during decel...is this normal, or a sticky valve? Also, actual boost tracks the spec pretty well, but seems to chronically read high at low boost values. Could the VNT actuator be a little sticky at the low end, or is this also normal?
Thanks again!
 

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A little tip on Read Measuring Value Blocks (MVB)

Its shows the Label File: at the top. The lbl filename is shown in blue if you click it, it shows all the measuring block numbers that can be shown for that component.

If it shows cbl files are encrypted then these files it don't show anything.
 

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My theory...........The written value is just that. The production line technician signing off and recording the value and verifying in writing that it is within the tolerance the factory allows on the assembly line. (maybe to be read by quality control further along the line, a bit like the yellow paint dabbed on other parts)

Now......the ideal torsion is 0 degrees and that allows the designed ideal valve timing and also the point that the injector reaches peak pressure. Remember the injector may be fired up to 40 degrees before top dead centre at high speed. If the cam is retarded that peak pressure may arrive too late to inject the required amount of fuel to provide the needed torque at speed.

At idle the injector peak pressure point is less important (it's always important of course) because of the short duration of the injection period.

Your fuel consumption at idle reduces with retarded cam timing because the exhaust valve stays closed for longer so more energy can be extracted from the combustion process etc..................................
 

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I would suspect that your EGR valve is sticking a little open. The EGR values recorded are not actuals. They are a calculated value given from the ECU maps. The MAF values are actuals. So if the EGR values are high, this reflects that too much EGR is being given, and it is being reflected in the MAF values. When mine failed I had very high EGR values. I also changed my oxygen sensor. I have read some BOSCH documents which say, 10 years or 150K miles is the normal useful life on the type of oxygen sensor we have in our diesels.
 

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Hi all.
Sorry to hijack this thread but I'm having a peculiar issue:
My torsion values bounce from 1.1 to 1.7. Is this usual?
Btw it's a 2002 Passat with an AVF engine.
I've checked for error codes and found none...
Many thanks in advance
 

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VIGGeN

First posts normally go in introductions else you could get a free fix and we never see you again!!!

Forum Rules and Guidelines


This is a new forum layout which is owned by a company 6 months ago that doesn't give a dam with loads of bugs which have been reported in the new thread. There is no TDI Wiki at the moment or original similes. It doesn't show the car spec/location.

We Are Live - Community Feedback

This has been talked about many times.

I've made a poll which no one has posted in, there are a few votes and comments.

Do you like the new forum features?

Wiki pages have been restored as of 7th December, I asked where is the link it should be on top of the main forum.

No error codes scanned with what a generic scanner or VAG-COM\VCDS?
 

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Registered
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VIGGeN

First posts normally go in introductions else you could get a free fix and we never see you again!!!

Forum Rules and Guidelines


This is a new forum layout which is owned by a company 6 months ago that doesn't give a dam with loads of bugs which have been reported in the new thread. There is no TDI Wiki at the moment or original similes. It doesn't show the car spec/location.

We Are Live - Community Feedback

This has been talked about many times.

I've made a poll which no one has posted in, there are a few votes and comments.

Do you like the new forum features?

Wiki pages have been restored as of 7th December, I asked where is the link it should be on top of the main forum.

No error codes scanned with what a generic scanner or VAG-COM\VCDS?
No error codes whatsoever... scanned with VCDS.
 
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