SuperVAG a VCDS diagnostic tools – effective troubleshooting of VW group vehicles - 1.9 TDI engine as an example
The VAG COM program among other functions has the ability to perform recordings. This is a strong feature when troubleshooting vehicle problems. The ability to use the program and a few measuring tips from the workshop will save every technicians time and trouble.
LOG recordings - purpose
A diesel engine requires for good performance the correct values at the correct time. Monitoring several values from different groups during a test drive is not possible. Another argument is that in the dynamic driving modes we can detect more faults, that will be described.
SuperVAG & VCDS - data recording procedure
After establishing communication with the engine ECU we select the groups that we want to record. For the basic and first engine performance test we select groups 003, 008 and 011.
Group 003 contains information about:
Engine speed, Air mass target, Air mass actual, EGR control solenoid duty cycle.
Important note:
The air mass value quoted as "requested" is in fact specified as in relation to the EGR valve and means that on the graph in the area below the trace line (that is when the engine is intaking at partial load this amount of ait) is a zone, where the control unit can activate the EGR system. To understand this as being a requested value by the control unit in all modes is a big and often very common mistake.
1. Air mass is positively too low
If the air mass sensor is giving correct readings, the cause could be in the low performance of the turbocharger (all possibly causes from a dfective turbocharger to a non-functional electropneumatic charge pressure actuator, etc). The problem could be in a leaking or non-fuctioning EGR valve. If the EGR valve is partly open the pressure in the exhaust system causes that the exhaust gases are flowing to the intake system and the engine at full load has no power and smokes heavily. The problem could also be caused by strong crankcase blow by of gases. To test this, remove the crankshaft ventilation hose from the intake manifold and let it blow into the atmosphere. The cause could be in a restricted air filter (a diesel engine requires a lot of air) or it could by a restricted exhaust (back pressure is present but the flow is restricted).
2. Air mass is OK but air mass sensor reading is incorrect
We test if the air mass sensor is defective in two ranges. In idle and at load in the following ranges 2500, 3000 and 4000 RPM. The air mass should achieve the correct values in all these ranges. During the test we should disconnect the air filter intake hose so that there is no restriction, we should have a disconnected EGR valve (before this we should check if the valve is closed), we should have a disconnected crankcase ventilation and a non-restricted exhaust system. A good idea is to have a verified air mass sensor that we can install for testing.
Log-file recording
The VAG COM program contains in the block of measured values a LOG function. When you activate the function a file name appears in the bottom line of the screen, that can changed to any required name. So the default name e.g. LOG-01-003-008-011.CSV can be changed to e.g. “SmithOriginal.csv”.
Default file format “LOG-01-003-008-011.CSV or your own name “SmithOriginal.csv”
this CSV file can be edited with MS Excel or another spreadsheet editor. Here are a few tips how to handle these files:
If the file doesn't sort properly into clear columns and looks like this:
Thursday,04,September,2003,16:11:49 038 906 019 KE ,,G000SG 4898, ,Group A:,'003,,,,Group B:,'008,,,,Group C:,'011 ,,RPM’s,Air/Stroke,Air/Stroke,Duty Cycle,,RPM’s,injected quantity, injected quantity, injected quantity,,RPM’s,(without units),(without units),duty cycle ,TIME,,,,,TIME,,,,,TIME,,,, MARKER,STAMP, /min, mg/R, mg/R, %,STAMP, /min, mg/R, mg/R, mg/R,STAMP, /min,,, % ,0.32,819,250.0,245.0,60.2,0.66,840,0.0,30.5,20.9,0.00,840,1044.0,984.0,19.9
,1.32,819,250.0,245.0,60.2,1.64,840,0.0,30.5,20.9,0.98,819,1044.0,984.0,19.9
,2.30,819,250.0,249.9,60.6,2.64,819,0.0,30.5,20.9,1.98,819,1044.0,984.0,19.9
You can be assured that your PC is not set correctly. Excel or another spreadsheet editor hasn't recognised the column separator and has put all the figures into one column.
Excel or your PC settings for correct column recognition
The VAG COM system uses the “comma” as the separator. So set your PC to use the correct separator. Go to START - Control Panel - Region and Language - Additional settings and in the List separator box change the setting to a "comma" (it's usually set to a semicolon"). If you're not confident with the PC ask somebody can change the settings. Now your log should show up correctly.
How to create a graph from the table, see the video in the "file" folder...
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