YJ Lean Error Code

cj777

cj777

Well-Known Member
Joined
Mar 22, 2005
Location
Durham, NC
I have a 91 YJ with a 60mm bored out throttle body, and fuel cell with an E8248 inline fuel pump...all new. Within the last few months I have replaced the coolant temp sensor, map sensor, and tps. I'm finally without error codes while idling. However when I drive it, especially if I give it a lot of gas I get an error code 51 -Oxygen sensor stuck at lean position. The engine does have a rough idle and is lacking power but otherwise seems to run ok. The code always clears when I turn the jeep off, but comes back during the next trip. I checked the injectors out and the all seem to have 16ohms of resistance. At idle I get about 38psi of fuel pressure at the rail with vacuum connected to the regulator and about 45 with it disconnected. Any ideas from the 4.0 gurus?
 
Take some .030 or so wire and back probe the connector at the oxygen sensor. Make sure to get the signal wire and ground, not the 5v feed.

Note or even video the voltage on a multimeter and post it up. This will verify whether the o2 sensor if functioning properly.
 
transman731 said:
do you have a way to monitor o2 sensor?
voltage has to stay below 0.5 volts for a period of time without toggling to set the code
Click to expand...

Mac5005 said:
Take some .030 or so wire and back probe the connector at the oxygen sensor. Make sure to get the signal wire and ground, not the 5v feed.

Note or even video the voltage on a multimeter and post it up. This will verify whether the o2 sensor if functioning properly.
Click to expand...

Would this need to be while driving, after the motor warms up, or while idling in the driveway?
 
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