I was wondering if anyone has any ideas for me beacuse i'm stumped. The following problem happens to my 93 Explorer 4.0L when its warm outside. but not when it is cold. it runs great in the winter but when it gets above 70 outside it will run REALLY rough and stall when i drop the revs below 2000. i have changed the following to brand new: spark plugs, wire, coil pack, TPS, crank case sensor, O2 sensors (both), and MAF.

The check engine light is on and the codes say that both O2 sensors are running both rich and lean! even after clearing the codes i get the same codes back. and this only happens when its warm outside. any help would be greatly appreciated.

 

One of the first tests when getting O2 sensor codes is to check the fuel pressure/fuel delivery system. If the pressure is too high, you get too much fuel into the cylinder and it runs rich. If the FPR has a ruptured diaphragm, you get too much fuel into the cylinder and it runs rich.

 

mrshorty, It would be running very richall the time, but it only happens when warm. I wonder if the intake air temp sensor is faulty.

 

It's possible. IAT and ECT are pretty easy to test, as they are simple thermistors. Measure the voltage drop across the sensor and then look up the temperature on this chart: www.xmission.com/~vondm/fordtempsensor.txt But I would still start with a fuel pressure test.

 

Did you ever resolve this problem? I have a 92 that is exhibiting the same symptoms but doesn't give me any codes except 111 (no error found). I have run codes several times. Truck also pings under load.
I have recently replaced many parts to cure other problems or as routine maintenance, including: fuel pump assembly, plugs, wires, MAF, IAC. Cleaning the intake didn't help either. Truck has 270K on it, but engine only has 55K.
IAT for me perhaps?