Mercury MerCruiser MCM 454 Mag MPI Service Manual page 798

SERVICE MANUAL NUMBER 23
Code 33 (2 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit (Scan)
High Signal Voltage
TEST DESCRIPTION:
Index
90-861326--1 MARCH 1999
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Number(s) below refer to step number(s) on the diagnostic table.
Step 2. This step will determine if there is an adequate vacuum supply to the MAP
sensor. If the vacuum gauge reading is erratic, refer to the "Rough or Unstable Idle" in
Troubleshooting section.
Step 4. This step simulates a DTC 34. If the ECM recognizes the low signal voltage and
sets a DTC 34, the ECM and wiring are OK.
Step 5. This step checks for an open in ground CKT 814.
STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
2 1. Ignition "OFF."
2. Install a vacuum gauge to manifold vacu-
um.
3. Start engine and raise RPM to 1000.
4. The vacuum reading should be steady.
Is the vacuum reading steady and above
the specified value?
3 Allow the engine to idle.
Does the scan tool indicate MAP sensor
voltage greater than the specified value?
4 1. Ignition "OFF."
2. Disconnect MAP sensor harness connec-
tor.
3. Ignition "ON," engine "OFF."
Does the scan tool indicate MAP sensor
voltage less than the specified value?
5 1. Ignition "OFF."
2. Connect DVOM from harness terminal
"A" (CKT 814) to harness terminal "C" (CKT
416E).
3. Ignition "ON," engine "OFF."
Does the scan tool indicate MAP sensor
voltage greater than the specified value?
ACTION
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
VALUE YES
PROCEED TO
– Step 2
14 in.
HG HG
(45.5 (45.5
kPa)
Step 3
4 Volts Step 4
1 Volt Step 5
4 Volts Step 10
Page 5G-53
NO
Go to
OBD
System
Check
Step 6
Step 7
Step 8
Step 9