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The Jeep Grand Cherokee is a mid-size luxury SUV produced by the American manufacturer Jeep. While some other SUVs were manufactured with body-on-frame construction, the Jeep Grand Cherokee has always used a unibody chassis.

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Codes PO108,PO 308 . As you know 108 is high circuit and the 308 is m8

jeep grand cherokee 4.7 liter. Have replaced Throttle position sensor, the MAT sensor, the crankshaft and Camshaft position sensor. also replaced the coil pack for number 8 and replaced alll plugs. My question is is there any change in things when I disconnect the MAP sensor from when it is installed. I am getting no change. Also when I am at idle in the park position and step on accelorater petal to the floor to 4000 rpm it is a strong indication of noticable misfire The misfire is acting like same sequence each few moments pop pop bu8mp bump bump

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Puan 1


@lwlambert instead of posting more questions about the same issues, it will help if you come back to those that have been answered

Rep: 25


I have a vacuum leak and am thinking it may be the throttle body. can i clean it without taking it off and how can i test to see if it is faulty


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@lwlambert stick with one question and do not open up any more questions about the same issue. This becomes really confusing. If you want people to help you, try to focus on the problem with one question. We need to clarify a few things. Your OBD scan code should be a 4 digit number so I assume that your codes are P0108 and P0308. Correct me if I am wrong.

“My question is is there any change in things when I disconnect the MAP sensor from when it is installed “ not sure what you are asking here. The P0108 code is a MAP sensor voltage too high. (Too low of a vacuum as seen by the PCM. This could be a vacuum leak at the intake, a fault of the MAP sensor, a worn engine or the PCM. I suggest you check the MAP sensor if you are not sure about it.

MAP Sensor Testing

Remove the connector at the MAP. There are three pins inside the connector (in a straight line). With the Key positioned to “On”and not start, you should see 5 volts across the outer two pins. This means that the PCM and wiring harness is good.

Reconnect the MAP sensor. Back-probe (with a paper clip) the center pin and connect the other end of the voltmeter to ground. With the ignition key On and the engine not running the voltage be 4 to 5 volts. Start the engine. The MAP should measure sometime 1 to 2 volts. Now open the throttle a bit and the voltage should increase with increasing rpms.

Definition of error code P0308 - Cylinder 8 Misfire Detected.  Some potential causes of the P0308 trouble code would include:

  • Faulty ignition parts such as the spark plugs, ignition coils, spark plug boots and wires, or distributors
  • Faulty fuel system parts such as the fuel pressure regulator, fuel injectors, or the EGR valve
  • A large vacuum leak
  • A faulty powertrain control module

You need to let us know what the #8 plug looks like. You also want to do a compression test as well as a leakdown test. Rule out your valves and head gasket etc.

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Puan 3


i unplugged the MAP sensor and there was no change. Shouldd something change?


Not if it is a good MAP sensor and your engine has other issues. Like I pointed out in my answer, measure the voltages and then you know if it is the MAP sensor or not.


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