#2482 - 04/05/0811:07 AMWhy a A4 transmission was not shifting correctly
Joined: Dec 2000 Posts: 5,240teamzr1 Owner - Pays the bills
teamzr1 Owner - Pays the bills Lives in Engine Bay
Joined: Dec 2000
Car owner decides to have some mods installed and tuned Car was tuned by Idaho Speed Center ( see Useless Vendors section" and engine not only ran like crap but the A4 would not shift correctly.
Owner contacted us for a custom tune and in having the owner do a testrun using the Ease OBD-II scanner and then sending us the recording to analyze we quickly found what is shown below.
Surprising no one who drove the car even saw this but the finding are.
C5 having a A4 trannie and the 2.73 rear end ratio had a 3.42 diff installed.
Problem was the diffs are different and with the 3.42 diff installed into the orginal transaxle case the sensor to pick up the VSS signal was now further away from the diff ring and thus random times the VSS signal was picked up incorrectly and thus PCM could not calculate the MPH correctly which means then the PCM could not properly compute when to make the auto shifts.
As seen at times the MPH would be correct and then MPH reported incorrectly yet throttle angle showed MPH should have been higher thus PCM would not make proper shifts
Again shows how important it is to own a OBD scanner and know how to analyze the data and also again proves if a vendor is charging you for a custom tune and does not even have a OBD scanner is run, not walk away from that vendor before they screw up you car