MAP Sensor Ground? - JeepForum.com
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post #1 of 49 Old 07-26-2017, 09:02 AM Thread Starter
Du510
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MAP Sensor Ground?

Hey guys - does anyone know where the MAP sensor grounds? Is it via the PCM? '97 4.0.


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post #2 of 49 Old 07-26-2017, 09:17 AM
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post #3 of 49 Old 07-26-2017, 09:22 AM Thread Starter
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Hmm?

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post #4 of 49 Old 07-26-2017, 09:24 AM
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Hmm?
Just be patient. There are couple members who are real good at electrical.
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post #5 of 49 Old 07-26-2017, 09:37 AM Thread Starter
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Just be patient. There are couple members who are real good at electrical.
Ah, thanks.

Hey where in Westchester are you? I'm just over the border in Putnam.

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post #6 of 49 Old 07-26-2017, 09:41 AM
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Hmm?
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post #7 of 49 Old 07-26-2017, 10:05 AM
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Don't know about the 97, but 05-06 is from the PCM, connector 2, pin 26 or 27 (there appears to be a discrepancy in the wiring diagram vs. the connector pinout), through the PDC fuse 28. So, yes, it could be from the PCM on yours if nothing significant changed between the years.
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post #8 of 49 Old 07-26-2017, 12:35 PM
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You have about 14 sensors including the MAP which ground through the PCM. They are all joined at 2 splice points then connect to the PCM.

If all other sensors are working normally & you suspect a bad ground at the MAP do a continuity test. If bad, there could be a bad splice causing high resistance.

The splice point for the MAP is S-127 located more or less near the back of the intake manifold. The wire color for all is brown/yellow.
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post #9 of 49 Old 07-26-2017, 01:34 PM Thread Starter
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Thanks guys. I'm suspecting a bad ground but could be a bad sensor itself.
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post #10 of 49 Old 07-27-2017, 08:52 AM Thread Starter
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Originally Posted by Rubi4MyMrs View Post
You have about 14 sensors including the MAP which ground through the PCM. They are all joined at 2 splice points then connect to the PCM.

If all other sensors are working normally & you suspect a bad ground at the MAP do a continuity test. If bad, there could be a bad splice causing high resistance.

The splice point for the MAP is S-127 located more or less near the back of the intake manifold. The wire color for all is brown/yellow.
Was just thinking about this, how you mention about 14 sensors to feed the PCM.

CKP
CMP
Intake / Charge temp
Coolant temp
MAP
TPS
O2 front
O2 rear
OPSU


Nine off the top of my head - what am I missing?

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post #11 of 49 Old 07-27-2017, 10:22 AM
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Quote:
Originally Posted by Du510 View Post
Was just thinking about this, how you mention about 14 sensors to feed the PCM.

CKP
CMP
Intake / Charge temp
Coolant temp
MAP
TPS
O2 front
O2 rear
OPSU


Nine off the top of my head - what am I missing?
Looking at my FSM (05):
Clockspring
Ambient Temperature Sensor
A/C Pressure Transducer (2.4L)
Battery Temperature Sensor
Intake Air Temperature Sensor
Throttle Position Sensor
Engine Coolant Temperature Sensor
Manifold Absolute Pressure Sensor
Variable Line Pressure Sensor
Transfer Case Switch (Rubicon)
Crankshaft Position Sensor
Fuel Pump Module
Vehicle Speed Sensor
Camshaft Position Sensor
Throttle Position Sensor
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post #12 of 49 Old 07-27-2017, 11:09 AM Thread Starter
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Originally Posted by JEK3 View Post
Looking at my FSM (05):
Clockspring
Ambient Temperature Sensor
A/C Pressure Transducer (2.4L)
Battery Temperature Sensor
Intake Air Temperature Sensor
Throttle Position Sensor
Engine Coolant Temperature Sensor
Manifold Absolute Pressure Sensor
Variable Line Pressure Sensor
Transfer Case Switch (Rubicon)
Crankshaft Position Sensor
Fuel Pump Module
Vehicle Speed Sensor
Camshaft Position Sensor
Throttle Position Sensor

Ambient air temp sensor - fancy!

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post #13 of 49 Old 07-27-2017, 11:25 AM
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Ambient air temp sensor - fancy!
Does the PCM do anything with that as far as engine operation or is that just to relay to the mirror (if installed)?
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post #14 of 49 Old 07-27-2017, 11:42 AM Thread Starter
Du510
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Does the PCM do anything with that as far as engine operation or is that just to relay to the mirror (if installed)?
I couldn't imagine it doing anything other than passing the info through to the dash (or wherever it comes out), given that manifold air temp is a separate reading.

I don't have one (nor a few of the others he listed), so I might be just blowing smoke here.

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post #15 of 49 Old 07-27-2017, 12:02 PM
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The sensors do not “feed” the PCM, they ground through the PCM which then goes through a noise filter before going to the chassis ground.

For your purpose it is not important except to isolate the possible bad ground, if that is even the problem. If it was at the PCM all sensors would be affected. If only one, the problem would be at or before the splice from that sensor.

For reference:

Crankshaft position sensor
Intake air temperature sensor
Throttle position sensor
Manifold absolute pressure sensor
Engine coolant temperature sensor
Vehicle speed sensor
Oil pressure sensor
Camshaft position sensor
Fuel pump module (fuel gauge)
Battery temperature sensor
Upstream heated oxygen sensors (some later yrs have 2)
Downstream heated oxygen sensors (some later yrs have 2)

Biffgnar, the compass/temp mirror, optional on later yrs, uses a separate sensor (behind the bumper) with the same name & does not use the PCM sensor ground circuit. In earlier yrs the FSM calls it an intake air temperature sensor & in my ’05 FSM the one under the hood is listed both ways (ambient & intake air).
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