VAGCOM Measuring guide

[iMation]

[Source] Multiple websites around

VAG-COM Datalogging for MY2001+ Audi/VW Vehicles...

Note: In order to have a log that will be valid, you will need to see at least a 3rd gear wide open throttle run from about 2500rpm until redline. Any lifting of the throttle during the run will result in inaccurate A/F numbers for the purpose of our evaluation.

Channel 1: Lambda Correction

This is a fuel correction table used by the computer when it senses the car richening and leaning from the programmed air/fuel tables. The numbers will be displayed as a percentage starting from 0% indicating NO fuel correction is needed. This means the car is doing what it has been asked to do. No fuel is having to be added or removed to maintain harmony. The computer can correct for these rich and lean conditions up to 25% or so. Note that seeing numbers higher than 0 does not necessarily mean your car is running dangerously rich or lean just because of a little correction. Positive numbers displayed indicate fuel is having to be added to compensate for lean conditions. Negative numbers indicate fuel is having to be removed to compensate for a richer condition. The lower the numbers the better. Numbers upwards of 20 indicate some real problems that bear much closer attention. Remember that lean is your ultimate enemy. Note: This channel can not be substituted for channel 31 which displays the actual air/fuel ratio. This channel displays the deviance or the correction from the a/f that is requested, but if the incorrect air/fuel is requested by the programming than one could still be running an unsafe air/fuel ratio and the computer would not correct for it. To determine the actual a/f that is being requested and achieved you would defer to channel 31. To determine if the vehicle is having to remove or add fuel to achieve that a/f you would rely on this channel.

Channel 2: Mass Air Flow Sensor (MAF)

This channel measures the grams per second or airflow taken into account by the MAF sensor. Input I have collected from tuners suggest that this is not a direct measure and depends on other sensors, so programming may be able to affect the g/s independent of changes to actual airflow. Nevertheless, while this may not be a reading that can completely state the airflow your car is taking in, it can provide a good estimate. This is a great log to look at if you suspect a common failure, the dying MAF sensor. On a chipped car one would expect MAF numbers to increase linearly as the car approaches redline. Your highest numbers will be seen at or near redline and are likely to be in the neighborhood of 160-180 g/s. Low numbers at redline such as 120 g/s are a good indicator your MAF is on the way out. Codes may not be thrown at this point. Terribly low or NO readings means she is dead.

Channel 4: Intake Air Temperatures

This channel displays the coolant temperature of the car and in the last column the intake air temperatures of the car. The intake air temperature sensor probe is located in the intake manifold just after the throttle body assembly. This sensor will measure the temperature in degrees Celsius of the air after it has passed through the intercoolers and is preparing to enter the motor to mix with the fuel. Unfortunately this channel is not ideal to be used to measure ultimate intercooler efficiency because this would require two probes to be installed on the vehicle, one to measure pre-intercooled air and another to measure the air post intercooler such as the case with this sensor we are dealing with for channel 4. On the other hand, being able to measure the post intercooled intake air temperatures will at least give us a general idea of the adequacy of the intercooling abilities as well as yet another heads up on the possibility of other problems with the car that would cause increased air temps post turbo compressor and intercoolers. Ideally the intake air should be as cool as possible, perhaps remaining at or below ambient temps. The intercoolers are designed to make use of the air flowing over the car to cool the intake air so it may be common to see temps begin to rise after a spirited driving regimen while the car is back at idle. Watching those temps rise while idling and then observing how quickly they once again reduce as the car goes underway gives some insight into the recovery rates of the intercoolers. In adddition, you may want to observe the temps througout a 3rd gear wide open throttle (WOT) run to see if the temps remain cool and stable. If the temps start to rise too high, this may be an indicator that an intercooler upgrade would be of benefit or a change in the state of the tune of the car is in order.

Channel 20: Ignition Knock Control-Timing Retard for Each Cylinder

This channel is very straight forward. You should see a field of 0s everywhere with a few possible spikes in retard up to 6 degrees retard. The number 0 in each of the cylinder boxes indicates NO timing retard is taking place. This means no timing is having to be removed by the computer as it senses knock. Now, what if you see some random numbers like "1.5" and "3" every once in awhile? This should be fine. If you were a tweaker, ideally you would want to find that point where you are able to use the most timing without triggering problems. Since most people do not mess with timing adjustments, we want to see as close to zero as possible though. Timing retard of greater than "6" would have me worried and I would want some further investigation and adjustments made. Running overly aggresssive timing will result in lower power (BTDC is adjusted down based on knock activity in channel 20) and is a major player in engine destruction.

Examples:

CAR RUNNING TOO MUCH TIMING

RPM CYL 1 CYL 2 CYL 3 CYL 4
2500 0 0 0 0
2750 0 0 0 0
3000 0 0 0 0
3250 3 0 1.5 4
3500 3 3 4 4
3750 4 6 6 6
4000 3 0 3 4
4250 6 6 6 6
4500 6 6 6 6
4750 6 4 6 4
5000 8 6 8 4
5250 2 8 6 8
5500 6 8 8 6
5750 8 4 6 6
6000 6 6 6 4
6250 8 8 8 8
6500 8 6 6 6
6750 6 6 6 6


CAR RUNNING AGGRESSIVE TIMING (performance tuned)

RPM CYL 1 CYL 2 CYL 3 CYL 4 Retard
2500 0 0 0 0
2750 0 0 0 0
3000 0 0 0 0
3250 0 0 0 0
3500 0 1.5 0 0
3750 3 0 0 1.5
4000 0 0 3 0
4250 1.5 1.5 3 3
4500 3 3 3 3
4750 1.5 3 1.5 1.5
5000 3 3 6 3
5250 0 1.5 3 0
5500 3 3 1.5 1.5
5750 3 4 3 1.5
6000 1.5 3 1.5 4
6250 3 3 3 3
6500 4 3 3 3
6750 1.5 3 1.5 3

CAR RUNNING VERY SAFE TIMING

RPM CYL 1 CYL 2 CYL 3 Cyl 4 Retard
2500 0 0 0 0
2750 0 0 0 0
3000 0 0 0 0
3250 0 0 0 0
3500 0 0 0 0
3750 0 0 0 1.5
4000 0 0 0 0
4250 0 0 0 0
4500 0 0 0 0
4750 1.5 0 0 0
5000 0 0 0 0
5250 0 1.5 0 0
5500 0 0 0 0
5750 0 0 0 0
6000 0 0 0 0
6250 0 0 0 0
6500 0 0 0 0
6750 0 0 0 0

[iMation]

Channel 31: Lambda Reading or A/F Ratio

This value is particularly important to be viewed and interpreted only when the car is under full throttle input as lifting up on the throttle will result in funky numbers. Take your log in third gear (or higher if your local authorities will allow) from 2500rpm or so until redline. The values you will see are: 1 = 14.7:1 ratio, .85 = 12.5:1 ratio, .75 = 11:1 ratio. As you have probably figured, simply multiply the lambda value by 14.7 to obtain the ratio. A car that runs 14:1 (lambda value of about .95) all the way up to redline on increased boost is running a bit lean. Conversely, a car that is running 10:1 (lambda value of about .70) from idle to redline is running a bit rich. Remember that lean is your ultimate enemy. Running too lean for too long will spell disaster for the motor. Ideally you would like to see the A/F pass linearly from the factory 14.7:1 at idle towards 13:1 in the mid rpms (3500rpm or so) to at least 12:1 at redline (NOTE: New FSI platforms are running approximately 10.5:1 at WOT). This would show a car that is getting good fuel mileage under easy driving, but richens up nicely as you wind it out under full throttle to redline. This would make you feel at ease driving the car under high load conditions at high speeds (freeway cruising at 120mph) or using the car for frequent track days.


Example of manifold injection performance tuned a/f ratio readings: (NOTE: New FSI will request richer mixtures than this such as Lambda = .75 up top):

RPM Lambda
2500 .99
2750 .95
3000 .95
3250 .95
3500 .90
3750 .90
4000 .90
4250 .85
4500 .85
4750 .85
5000 .85
5250 .85
5500 .85
5750 .85
6000 .80
6250 .80
6500 .80
6750 .80

Channel 34: Exhaust Gas Temperatures (EGT)

Pretty straight forward here and a great channel to use to give you the heads up that other things are going wrong. This monitors the exhaust gas temperatures of the car. You want to see what the limits are here and it will take some beating on the car to find it. When the car is still warming up, your readings may not accurately reflect just how high these temps can get. Take your car out for some spirited full boost runs, then start logging in the normal 3rd gear WOT manner. Exhaust gas temperatures at 900 degrees Celsius and below are common for our engines when heavily boosted. This sensor appears to be only accurate up to 999 degrees Celsius or so. If you see readings creeping up this high, you have a great indicator that something is not right on your car and your engine is not happy with you. Running too high of temps for too long will spell disaster.

Channel 115: Requested Boost and Actual Boost

This is a very helpful channel for diagnosing boost leaks, trying to figure out why your car went into limp mode, and seeing if the software or hardware (electronic or manual boost controllers) are doing what they should be. This channel displays the boost requested by the computer (requested boost) in the first column and the boost actually made by the turbo (actual boost) in the second column. The readings you will see here can be misleading. First, you should know that the numbers you will see are not yet corrected for atmospheric pressure (about 1040mbar at sea level). The atmospheric pressure seen at the boost sensor is tough to estimate with complete precision, but I have found that subtracting 1000mbar from the numbers gets you close enough to actual boost unless you are living at 20,000 feet above sea level. The next thing you have probably noticed about these numbers are that they are displayed in mbar instead of psi like we are all used to. Well, this won't be a problem thanks to the metric system. 1000mbar = 1 bar and 1 bar = 14.5psi. There you have it.

So, can we all figure out what boost level in psi this car is requesting and making at 3000rpm?

RPM Requested Boost Actual Boost
2500...2100...1800
2750...2200...1950
3000...2200...2250
3250...2200...2200
3500...2200...2100

The correct answer is:

The computer is requesting 1.2 bar of boost at 3000rpm. This can also be expressed as 17.4psi.

The turbo is boosting 1.25 bar of boost at 3000rpm. This can also be expressed as 18.1psi.

So why are the above numbers important to us other than acting as a boost guage to entertain us? Well, as you can imagine, if you had a boost leak you would have a car that is requesting the correct boost but you would see very little in the actual boost column. In the case that you had just installed your new little boost controller or N75 valve you could do some logging to find that your actual boost was far exceeding your computers' requested boost numbers causing your car to go into limp mode due to it's sensing an "overboost condition. For those of us who dare to run a turbo that was not designed specifically for the software they are using, this is a great way to see why it is not working out for you. For example, the boost maps on a K03 will show the ECU requesting max boost at around 3000rpms (this is a small turbo that makes its boost low in the rpm range). Now if you were to throw on a Garrett gt28r or T28 turbo or even larger you would see that the computer will still request the max boost at 3000rpm, but the turbo is not capable of making it's max boost until closer to 3800rpm leaving you with an "underboost" condition.

NOTE: The sensor will only measure up to 2540mbar including atmospheric pressure. This means that if you are running more than 1.5bar or 21.75psi of boost this sensor will not measure beyond it. Both values will show maxed out at 2540mbar.

[Ant1981]

Those channels, are they the measuring blocks?