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Questions and Answers

Jeep Grand Cherokee Runs Bad Warm

Q. Mr Ciulla, I have a:

  • 1995 Jeep Grand Cherokee Laredo
  • 4.0 liter
  • Automatic transmission with 4WD
  • 170,000 miles
  • ABS
  • P/S, A/C, Cruise
Jeep Grand Cherokee Runs Bad Warm

It has been running great with normal preventative maintenance until about two months ago when one day it wouldn't start. Thanks to you I learned how to check the trouble codes and the Crankshaft Position Sensor (CPS) was the culprit. The day I fixed that part the Jeep started right up, but after about 15 minutes it started running very rough and would barely move under its own power.

After a couple of hours of double-double checking my fix, I always doubt myself first, I discovered that it started fine, but shortly after the engine warmed up the symptoms would return (missing, backfires, etc). My repair manual pointed to an O2 sensor and possibly the catalytic converter. My local mechanic agreed. Since the converter had started to rattle, one of the baffles broke loose, I replaced both.

Well, the Jeep runs better, but it still misses after it warms up though not nearly as bad as before. It will reach speeds of about 50 MPH, but it is a very uncomfortable feeling with the engine missing. I have looked over the ignition system and all the vacuum lines I can find and I have no trouble codes from the PCM. I have also checked some of the fuel system, relay, power to injectors, fuel pump.

Since I am currently living in the UK, I have no US spec Jeep experts to take it to and I can't comfortably drive it farther than ten miles for risk of it getting worse or really breaking something in the engine. Any help or advice you could offer would be greatly appreciated.

Thanks for you time.

A. There is no adjustment to the CPS, but on some models, two bolts are used to secure the CPS to the transmission. These bolts are specially machined to correctly space the sensor to the flywheel. Do not attempt to install any other bolts.

At this point I would suspect a bad Coolant Temperature Sensor (CTS). If it is telling the PCM the engine is running hotter than it actually is, the PCM will lean out the fuel mixture causing the engine to run lean and possibly causing the problem you describe. The CTS threads into the thermostat housing.

Additional Information provided courtesy of AllDATA

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© 2005 Vincent T. Ciulla

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