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1999 Jeep Cherokee fuel to rich?

Tiny
BUTTERSUGAR
  • MEMBER
  • 1999 JEEP CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
Jeep doesn't want to start. Sometimes it starts after cranking for a long time, but it runs rough and if you try to accelerate it dies. Checked the spark plugs and they're carboned up really bad. I've changed map sensor, distributor, camshaft sensor, crankshaft sensor, O2 sensor, computer and nothing seems to help. It has a 107 OBD code which says a low map sensor voltage. Anyone have any ideas?

Thanks, Robert
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Friday, October 31st, 2014 AT 4:16 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
The manifold absolute pressure sensor isn't working properly. However, the engine should start. It may run rough, but should run,

As far as the problem, either the sensor itself is bad, there is a broken wire, the connector is loose or corroded and not making a good connection, of the ECM could be bad.

This sensor is responsible for supplying manifold pressure to the ECM. Based on the signal it supplies, the computer adjusts air / fuel mixtures for optimum performance.

Tell me, have you checked to make sure the fuel pressure is within spec? Will it start if you use starting fluid?
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Friday, October 31st, 2014 AT 5:38 PM
Tiny
BUTTERSUGAR
  • MEMBER
  • 3 POSTS
First of all thank you very much for responding to my question. I don't think it is the ECM because it's been replaced. The map sensor has been replaced twice, so that shouldn't be the problem. The fuel pump pressure has been tested also. I haven't tried starting it with starter fluid, but I'll give that a try in the morning. I will also check for a broken wire or bad connection on the map sensor. Thanks again for your help, Robert
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Friday, October 31st, 2014 AT 9:19 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Robert:

I'm glad to help. Let me know what you find.

Joe
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Saturday, November 1st, 2014 AT 6:30 PM
Tiny
BUTTERSUGAR
  • MEMBER
  • 3 POSTS
Hi there Joe, Just wanted to let you know that my problem was the timing. My son-in-law had installed the distributor wrong.
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Monday, November 3rd, 2014 AT 7:16 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
That will do it! I'm glad it's fixed. Let me know if you have questions in the future.
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Tuesday, November 4th, 2014 AT 8:48 AM

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