Hey everyone! My son has a 2003 Jeep Grand Cherokie 4wd that I have a interesting ground reading . It has a po302 map sensor output high reading along with a couple of O2 sensors reading output high. Measuring the voltage to the MAP sensor I have the 5 Volts and the output is 1.2 to 1.3 Volts . Now here is the interesting part. When the motor is not running the ground on the map sensor reads 0 ohms. But when the motor is running The ground Jumps all around from about 50 ohms to 2 to 3 K ohms. It is grounded through the ECU . Does anyone know if that is a direct ground connection or does it go through a circuit to ground ? I've never seen a continuity test do this before. Thinking there is a problem with the ECU or wiring to it. Any other ideas as to what might be troughing this MAP sensor in a tizzy ? 2 of the O2 sensors that have the code on them have been replaced but still come back. For sure it's dumping too much fuel and running rich and poorly .

 

Test for voltage on the ground wire, engine running.

 

Thank you for the suggestion. No Voltage on ground, so we dug a bit deeper found some moisture on the dipstick, and on the oil cap and fill tube. Took some plugs out running rich and brown, sent a camera down some cylinders # 5 has liquid dripping down and one has piston wash. So sent it to the mechanic which rebuilt the motor and sold the car to my son. He's working on it and we'll see what happens. Personally I think head gasket or crack in head, or he didn't get the head bolts tourked correctly.