aNUT
Vendor , w/Business number
Sometimes it's good to have a refresher. I frequently get questions about optimizing mileage, or see threads about reduction in mileage after a timing belt change. This post addresses timing subtleties on VE cars, '96-'03 in North America.
Firstly, here's a screen by screen, step by step, pictorial on checking static timing with VCDS:
Connect the Vagcom to the OBD2 port located
a) above your left shin if you have an A4
b) behind the windshield wiper switch if you have a B4
c) next to the ash tray if you have an A3
Open VCDS.
Click "select"
Click "engine"
Wait for VCDS to establish a connection with the ECU.
Once in a blue moon, VCDS won't do this with the car running. If this is the case, turn the car off, then the ignition to on, (but not start) make the engine controller connection, start the car, and continue.
Click "measuring blocks"
Select group 000. Click "go". Click "switch to basic settings".
Click "TDI Timing"
The following graph will appear.
From the drop down menu in the lower right corner, select your engine.
The apex of the horizontal and vertical yellow lines is where the timing is set. If there are no yellow lines, the timing is very retarded. If there is only a vertical yellow line, the timing is very advanced. Sometimes on A3s and B4s VCDS gets confused when the timing is very retarded, and plots it as very advanced. Advance the timing, and the graph will 'come around.'
Adjusting the timing will not be covered in this how to. Please refer to the timing belt procedure for your car regarding how to do so. A3/B4 A4
Note that timing should be checked with the vehicle at operating temperature. The timing graph is graded by fuel temp, but advance rises slightly (~.5*) after the motor warms up.
OK, so that's the basic stuff out of the way. Before you're bored and move onto the next thread on oil banter, here's where the subtleties come in. Technically, with the apex between the red and green diagonal lines, timing is within spec. TDIclub dogma dictates that the driver wants the timing as close to the green as possible. The following photo is often referenced. The reason people claim this is optimal is to reduce EGTs. This is not true. More on that later.
Let's have a look at measuring blocks -> group 004. This shows actual and specified start of ignition.
Note that the actual start of injection cannot match specified with advanced timing. The Advance Solenoid/Cold Start Valve/N108 duty cycle is pegged at 2.8%. That means the minimum amount of advance is 2.6*. So what you say? Here's the rub. At light load, say 70mph on level ground, where one will get the best milage, specified advance will be .5*-1.5*BTDC. If the ECU cannot achieve requested (optimal) advance, economy suffers to the tune of ~5%. For us TDI nerds, 2-4 mpg matters.
So here's how I time cars:
I put the timing in the graph, then I look at group 004. I set the timing as advanced as I can get it, but retarded enough that actual can meet specified start of injection at idle.
And here's the graph with optimal timing:
Notice that I'm not even above the blue! On a cold day with not so stellar fuel in the tank, that apex can be a dotted white line or so above the red. This is very counter to the theory that's been propogated on these forums...but the car is more efficient.
Now, about that whole EGT thing. Shorter injection duration and earlier start of injection does reduce EGTs, but setting the static timing advanced doesn't achieve this. Higher injection pressures coupled with tuning that's optimized for the fueling hardware on the car does, but not advancing the timing.
Below is a log taken from my car at WOT and stratospheric (for a diesel) engine speed. These are the conditions that require maximum advance I've cropped off the speed, but this section of the log was taken between 3600 and 4600 RPM. It's clear that the car is only requesting a bit more the 13* advance, and the car can easily achieve over 15*. The Duty cycle (also not shown) is between 70-85%, so more can be had if necessary. Essentially, setting the timing for optimal economy does not sacrifice advance during high load situations as once thought.
The above graph was generated using JollyGreenGiant's superb plotting software.
Firstly, here's a screen by screen, step by step, pictorial on checking static timing with VCDS:
Connect the Vagcom to the OBD2 port located
a) above your left shin if you have an A4
b) behind the windshield wiper switch if you have a B4
c) next to the ash tray if you have an A3
Open VCDS.
Click "select"
Click "engine"
Wait for VCDS to establish a connection with the ECU.
Once in a blue moon, VCDS won't do this with the car running. If this is the case, turn the car off, then the ignition to on, (but not start) make the engine controller connection, start the car, and continue.
Click "measuring blocks"
Select group 000. Click "go". Click "switch to basic settings".
Click "TDI Timing"
The following graph will appear.
From the drop down menu in the lower right corner, select your engine.
The apex of the horizontal and vertical yellow lines is where the timing is set. If there are no yellow lines, the timing is very retarded. If there is only a vertical yellow line, the timing is very advanced. Sometimes on A3s and B4s VCDS gets confused when the timing is very retarded, and plots it as very advanced. Advance the timing, and the graph will 'come around.'
Adjusting the timing will not be covered in this how to. Please refer to the timing belt procedure for your car regarding how to do so. A3/B4 A4
Note that timing should be checked with the vehicle at operating temperature. The timing graph is graded by fuel temp, but advance rises slightly (~.5*) after the motor warms up.
OK, so that's the basic stuff out of the way. Before you're bored and move onto the next thread on oil banter, here's where the subtleties come in. Technically, with the apex between the red and green diagonal lines, timing is within spec. TDIclub dogma dictates that the driver wants the timing as close to the green as possible. The following photo is often referenced. The reason people claim this is optimal is to reduce EGTs. This is not true. More on that later.
Let's have a look at measuring blocks -> group 004. This shows actual and specified start of ignition.
Note that the actual start of injection cannot match specified with advanced timing. The Advance Solenoid/Cold Start Valve/N108 duty cycle is pegged at 2.8%. That means the minimum amount of advance is 2.6*. So what you say? Here's the rub. At light load, say 70mph on level ground, where one will get the best milage, specified advance will be .5*-1.5*BTDC. If the ECU cannot achieve requested (optimal) advance, economy suffers to the tune of ~5%. For us TDI nerds, 2-4 mpg matters.
So here's how I time cars:
I put the timing in the graph, then I look at group 004. I set the timing as advanced as I can get it, but retarded enough that actual can meet specified start of injection at idle.
And here's the graph with optimal timing:
Notice that I'm not even above the blue! On a cold day with not so stellar fuel in the tank, that apex can be a dotted white line or so above the red. This is very counter to the theory that's been propogated on these forums...but the car is more efficient.
Now, about that whole EGT thing. Shorter injection duration and earlier start of injection does reduce EGTs, but setting the static timing advanced doesn't achieve this. Higher injection pressures coupled with tuning that's optimized for the fueling hardware on the car does, but not advancing the timing.
Below is a log taken from my car at WOT and stratospheric (for a diesel) engine speed. These are the conditions that require maximum advance I've cropped off the speed, but this section of the log was taken between 3600 and 4600 RPM. It's clear that the car is only requesting a bit more the 13* advance, and the car can easily achieve over 15*. The Duty cycle (also not shown) is between 70-85%, so more can be had if necessary. Essentially, setting the timing for optimal economy does not sacrifice advance during high load situations as once thought.
The above graph was generated using JollyGreenGiant's superb plotting software.
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