The 20Vt 3B, AAN, ABY and ADU use a manifold absolute pressure (MAP) sensor to provide a pressure signal for the ECU to decide what to do with regard to timing and fueling. This MAP is located in the ECU that is up under the passenger side (LHD) footwell.


The sensor itself is a pressure transducer that converts an input voltage to an output voltage based on the degree of pressure that is placed on it, as described below:



The 3B (200 20vt and early S2) came with a 2 Bar (200 kPa) MAP. The AAN (UrS4 and S6)and ABY (later S2) came with a 2.5 Bar (250 kPa) MAP. The RS2 (ADU) came with a 3 Bar (300 kPa) MAP. All of the factory MAPs were made by Bosch.

Here is a photo of a stock 2.5 Bar (250 kPa) MAP sensor in a Stage 1 chipped UrS6 ECU (same MAP sensor for the stock UrS4):

Photo courtesy of Chapel.

If you want to upgrade an AAN to go above about 260 hp (Stage 1) to 280 hp (Stage 1+) and above, you will need to go to a 3 Bar MAP, or above. To do that, you will have to retrieve and open your ECU. Here are some links how to do this:

Link to instructions to remove the ECU from Jimmy Pribble's old UrS4.com website
Link to instructions to open the ECU from Bob Myers' Chips-Ur-S website

Here is a photo of an open AAN ECU showing the MAP sensor (the Black box with the black hose leading to the brass nipple that is connected to a hose from the intake manifold):



Here is a tighter shot of a different ECU, showing the Bosch 3 Bar MAP and suspected Lehmann Stage 1+ chips:



If you want to upgrade your chipset above Stage 1 but you can't find a 3 Bar Bosch MAP sensor, then your alternative is a VMAP, i.e. a variable MAP sensor. This is all electronic and was developed by Feico VanderLaan, and avaiable through MoreBoost.com and its dealers:

Link to the VMAP website

Here is a VMAP:



Here is the VMAP installed with some MRC chips by Bob Myers at Chips-Ur-S (an MRC and VMAP dealer):



This will be on the exam