Code 33: Manifold Absolute Pressure (MAP) Sensor Circuit (Scan)
(1 of 2)
814
BLK
ECT
MAP AND ECT
GROUND
CIRCUIT DESCRIPTION:
DIAGNOSTIC AIDS:
The Manifold Absolute Pressure (MAP) sensor re-
sponds to changes in manifold pressure (vacuum).
The ECM receives this information as a signal volt-
age that will vary from about 1-1.5 volts at closed
throttle idle, to 4.0-4.8 volts at Wide Open Throttle
(W.O.T.) (low vacuum).
If the idle is rough or unstable, refer to “Troubleshoot-
ing” for items which can cause an unstable idle.
With the ignition ON and the engine OFF, the man-
ifold pressure is equal to atmospheric pressure and
the signal voltage will be high. This information is
used by the ECM as an indication of vessel altitude
and is referred to as BARO. Comparison of this
BARO reading, with a known good vessel with the
same sensor, is a good way to check accuracy of a
“suspect” sensor. Reading should be the same, + .4
volt.
The scan tool displays manifold pressure in kPa of
pressure and voltage. Low pressure (high vacuum)
reads a low voltage while a high pressure (low vacu-
um) reads a high voltage.
IftheMAPsensorfails,theECMwillsubstituteafixed
MAP value and use engine RPM to control fuel deliv-
ery.
An intermittent problem may be caused by a poor or
corroded connection, rubbed through wire connec-
tion, a wire that is broken inside the insulation, or a
corroded wire.
TEST DESCRIPTION:
Any circuitry that is suspected as causing the inter-
mittent 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 har-
ness. After repairs, clear codes following “Clearing
Codes” in “ECM Self-Diagnostics.” Failure to do so
may result in codes not properly being cleared.
Number(s) below refer to circled number(s) on the
diagnostic chart.
1.
Engine misfire or a low unstable idle may set
Code 33. Disconnect MAP sensor and system
will go into backup mode. If the misfire or idle
condition remains, refer to “Troubleshooting.”
2.
If the ECM recognizes the low MAP signal, the
ECM and wiring are OK.
Index
5C-106 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
90-823224--2 796
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1993, 1994, 1995, 1996, 1997 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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