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Q: Runs good for first half hour or so then starts to hesitate and lurch

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Runs good when I start up, nice and strong. After about a half hour or so of running it starts to gallop, then hesitates and lurches when I accelerate. Changed fuel injectors thinking that might be the problem, but still having this issue

My car has 205431 miles.
My car has an automatic transmission.

A: When we have symptoms that show up after th...

When we have symptoms that show up after the car warms up, it is definitely temperature related. There is an important factor here that will need to be considered. A cold motor is operating in what is called open loop. This is a preprogrammed fuel and air metering that allows the motor to run cold. Once the motor reaches a specified temperature, usually about 160 degrees Fahrenheit, it will switch to closed loop and utilize the many sensors to calculate the air fuel ratio. Switching from open to closed loop usually only takes a few minutes unless there is a problem with the thermostat or you live in below zero conditions. If your car is slow to warm up, the problems that could be disguised are vacuum leaks or fuel supply issues.

If your Cherokee is warming up properly, it can be any of the following:

  • cap
  • rotor
  • plug wires
  • crank sensor
  • cam sensor
  • MAP (manifold absolute pressure) sensor
  • PCM (powertrain control module)

All of these are susceptible to problems as your Jeep warms up. The best method to determine what is happening is by connecting a scanner and monitoring the scan data when the problem begins.

Diagnosis of this will require access to wiring diagrams, components locations, component specifications, a test light, scanner and multimeter. If you have access to these, you should begin be looking for codes and inspect the scan data.

If you need assistance with diagnosis or repair of this issue, a certified YourMechanic technician can come to your location to perform an inspection of your car’s hesitating issue to help diagnose and repair this for you. Good luck!

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