The 3-Bar MAP sensor can measure boost levels up to 28 PSI and replaces the standard Mopar Turbo I/II 2-bar MAP (14-15 PSI) sensor. The stock Normally Asphyxiated TBI uses a 1-bar MAP for its required range of 30 - 0 inches Hg vacuum.
Regardless of whether 1, 2 or 3-Bar MAP sensors are used, each range of MAP sensor still generates a signal between 0.5 to 4.9 vDC, depending on engine load. On a stock Chrysler 1990-91 SBEC the ECM monitors the 2-BAR MAP voltage for over-boost shutdown. Safe, rapid, engine shutdown automagically occurs (via the ASD relay) whenever manifold boost pressure exceeds the factory-programmed set point within the SBEC. This occurs roughly somewhere around 4.74 vDC (MAP sensor signal output) or approximately 13 - 14 psi relative manifold pressure (Mopar factory calibrations vary by year and turbo/drivetrain configuration).
A very inexpensive (unless you don't increase fuel flow) way to defeat the over-boost shutdown is to use a fixed-value 4.7 vDC Zener Diode (available at Radio Shack). When properly wired to your 2-Bar MAP sensor, this will effectively 'hold' the MAP signal below overboost shutdown, regardless of how high actual boost levels increase.
Another way to "hold" or "clamp" the MAP output is to get a Boost-Cruncher from Mike or Ryan at Forward Motion. Developed by Carroll Supercharging the variable-value Boost-Cruncher, works on the same principle as the fixed-value Zener Diode put permits remote mounting, say within your glove box or on your console. More importantly, since it can be easily user-adjusted within a 2.5 to 4.9 vDC range, the "BC" provides more flexibility for retaining over-boost safety-shutdown, but now at desired higher boost levels. "BC" is compatible with 1, 2, or 3-bar MAP sensors. It also provides a yellow LED indicator to show when it's "clamping" threshold has been reached.
GM's AC-Delco division has a 3-Bar MAP sensor that was used on the 1989 Turbo
Trans AM 3.8L V6. It is P/N 1#213-101 (1#1604-0749). This sensor
must be used in conjunction with an intercooler, larger injectors, and a custom
calibration, FWD Performance Stage 4 SBEC. The custom SBEC calibration achieves higher than
2-bar ECM (wastegate) controller
boost levels without resorting to 4.7 vDC zener diodes or adjustable bleed valves
to "trick" the EMC. Click on the graph
to view Chris Robertson's MAP spreadsheet data..
When looking at the GM 3-Bar MAP sensor with the vacuum port facing you (front, as shown below), the three connectors are from left to right, "A, B, and C." The solid red lines indicate the "key-way" positions on the GM sensor. Note: the connector latch at the bottom of the sensor,
Usually, GM 3-BAR sensors have these connections stamped on the rear side of the sensor.
Physically, you will need to cut a small notch in the vehicle's gray (male) harness connector to match the "A" key-way on the GM map sensor. (The stock gray Weather-pak connector already has key notches in the "B" and "C" terminal positions). The notch can be carefully cut with a sharp knife blade on the (A) terminal with the BLACK wire with LIGHT BLUE tracer, as shown:
Double check the wiring to insure the harness connector wiring matches the sensor/ECM as follows: