Questions and Answers

Jeep YJ Dies In The Desert Q. I have a 1994 Jeep YJ. 4.0 liter L4, 5-speed and 100,000 miles, that starts backfiring through the intake and pretty much dying after being run for a few hours in air temperatures above 100°. If I pull over for 10 or 15 minutes it will run fine for another 10 or so if the air temperature is still hot.

A normal place for this to occur is coming down I395 in California during the summer. If I leave Bishop and drive straight through, by the time I get to Adelanto, three hours across the desert, it will start to miss, real slight at first and then will get to the point I have to pull over. But it will idle fine for ever.

Once I drop off the summit into LA, and the air temperature drops, it will run fine again until the next desert trip. In the winter, this same trip has no problems at all. Mind you, the temperature gauge is showing a nice 185° to 190°.

I have had the gauge checked, parts already replaced include and were not necessarily related to this problem, but you may find helpful: Borla Header, K&N intake, O2 sensor, cap, rotor, wires, optima battery, radiator, hoses, thermostat, head gasket, rear main seal. And probably a few others I have forgotten.

The dealer can't help, because once I get back home to cooler weather, it runs fine and does not show any codes.

Forest

A. Since it seems the temperature is the root of the problem, I would have to suspect either the Coolant Temperature Sensor or the Air Intake Temperature Sensor.

It seems what's happening is one of those sensors are indicating to the PCM that a temperature is higher than it actually is and the PCM is leaning out the fuel mixture to compensate.

Both are cheap and easy to replace, so I would go with that first.