DF - Testing Notes

NOTE: You should enter this Pinpoint Test only when you have been directed here form Quick Test or Pinpoint Test S.

REMEMBER

To prevent the replacement of good components, be aware that the following non-EEC areas may be at fault.

- Unusually high/low barometric pressure.

- Kinked or obstructed vacuum line (MAP).

- Basic engine (valves, vacuum leak, timing, EGR valve, etc.)


This Pinpoint Test is intended to diagnose only the following:


- MAP/BP sensor

- Harness circuits: VREF, MAP/BP, and SIG RTN

- Processor assembly

- MAP vacuum line


DESCRIPTION


The Manifold Absolute Pressure (MAP) sensor operates as a piezoelectric (pressure-sensing) disc. However, rather than generating a voltage, its output a frequency change. The sensor changes frequency relative to intake manifold vacuum. The sensor frequency increases as vacuum increases. The MAP sensor allows the EEC processor to determine what the engine load is. Its signal affects air/fuel ratio, ignition timing, EGR flow and altitude compensation.

The BP sensor is used to sense the changes in barometric pressure, allowing the EEC processor to sense the altitude at which the vehicle is operating. Its signal affects air/fuel ratio, spark and EGR for altitude compensation.