Caprice V6-262 4.3L (1987)
Fig. 004 - Wiring Diagram for Chart C-1D MAP Output Check. VIN E, VIN Z
CHART C-1D
MAP OUTPUT CHECK
5.0L (VIN E) "F" SERIES (TBI)
4.3L (VIN Z) "B & G" SERIES (TBI)
Circuit Description: The manifold absolute pressure sensor (MAP) measures manifold pressure (vacuum) and sends that signal to the ECM. The
ECM uses this information for fuel and spark control.
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1.
Checks MAP sensor output voltage to the ECM. This voltage, without engine running, represents a barometer reading to the ECM.
2.
Applying 34 kPa (10 inches Hg) vacuum to the MAP sensor should cause the voltage to be 1.2 volts less than the voltage at Step 1. Upon
applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3.
Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to the MAP hose.
Diagnostic Aids: With the ignition "ON" and the engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will
be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading
with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same, ± .4 volt.
