1994 Jeep Grand Cherokee Limited V8 - Os Sensor Issue

So this little gem of an SUV has been good enough to me over the year that I have had it, but it is one of those used vehicles that has me scared to look underneath cause there is always something amiss.

I have been having some power problems and the OBD check engine light has been coming on. The engine like to putter like its not getting enough fuel from a clogged fuel filter when it gets going, hot or cold. Have confirmed that the fuel pump is with proper voltage and pressure. Though haven’t noticed a big difference with the new filter. The check engine light cycles a code of 21, which is refinanced to the O2 sensor, both upstream and down stream. That tells me that there are TWO O2 sensors for this model. And research has confirmed this. One ahead of the cat and one behind the cat.

Heres the kicker, I only have one O2 sensor at the head of the cat and the location of where the second one would be located is only a solid section of pipe from cat to muffler. I haven’t been able to track down the plug connection for the second sensor and these codes and problem only came after I gave the Jeep a tune up.

I’m wondering if there is going to be long term damage to the engine if I don’t resolve this matter? Anyone have any experience with something similar to this?

This is an OBD I vehicle. I don’t think many (if any) vehicles in 1993 had a “downstream” sensor. The setup was a lot more primitive compared to OBD II before it was standardized and regulated. Since you have a V8, it’s much more likely that there are two sensors, one for each bank of cylinders.

What did you do for the tune-up?

Distributor cap, rotor, rotor sensor, plugs, and wires. Did double check the plugs and set gap to proper spacing. The sensor is aftermarket though I’m not sure what a “bad” sensor would cause. Though seems like the tune-up would seem to be the driver of this new mystery.

As long as I don’t have to look under the vehicle again the happier I will be. The previous owner had strapped the fuel filter on with zip ties…might be time to run a magnet along the body to see where the bondo is.

OBDII wasn’t required prior to the 1996 model year. Ergo, no need for downstream oxygen sensors. All they do is monitor the performance of the cat converter for the OBDII system.

Codes are imprecise. There are two O2 sensors on this vehicle… one for bank 1 and a second for bank 2. I suspect that’s what you’re reading. Bank 1 is for one bank of cylinders (one exhaust header or header pipe), bank 2 for the other.

Power problems could also be from a plugged cat, whch would restrict exhaust flow and might set the check engine light. Maybe just coincidence that it became noticeable after the tuneup.