Mercury MerCruiser MCM 454 Mag MPI Service Manual page 708

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SERVICE MANUAL NUMBER 23

Code 33 (1 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit (Non-Scan)

CIRCUIT DESCRIPTION:

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure

(vacuum). The ECM receives this information as a signal voltage that will vary from about

1-1.5 volts at closed throttle idle, to 4-4.8 volts at Wide Open Throttle (low vacuum).

If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the engine rpm

to control fuel delivery.

DIAGNOSTIC AIDS:

An intermittent problem may be caused by a poor or corroded connection, rubbed through

wire connection, a wire that is broken inside the insulation, or a corroded wire.

Any circuitry that is suspected as causing the intermittent complaint should be thoroughly

checked for backed-out terminals, improper mating, broken locks, improperly formed or

damaged terminals, poor terminal-to-wiring connections, corroded terminals and/or wiring,

or physical damage to the wiring harness. After repairs, clear codes following "Clearing

Codes" procedure at the front of this section. Failure to do so may result in codes not

properly being cleared. If Code 14 is also set, check for open ground CKT 814.

90-861326--1 MARCH 1999

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Manifold Absolute Pressure (Vacuum)

To ECT Sensor

To TP Sensor

Map And ECT Ground

TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI

Voltage Range

Chapters

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