Renix o2 sensor problems

Some back story. Newly rebuilt motor .020 over. New fuel pump. 4 hole injector upgrade. No cat with just a resonator.

Here is the problem. The o2 reading is 5v with key. When i start the vehicle it slowly goes to around 3.2v but wont bounce. I can watch the computer on the scanner and it slowly starts leaning out the motor trying to go on closed loop but it starts chugging and returns to open loop then runs good. It will do this cycle 4 or 5 times then stays in open loop until i resart it. I have good 13.8v to heater when running and a good ground. Heater circuit has 15ohms at the sensor with it unhooked. If i boost the fuel pressure by unplugging the regulator it makes no change.

Monitoring the o2 driving down the road it will go closed loop and start bouncing great but as soon as i let off the gas it goes back into open loop and the fumes are really rich. Ive read everything i can and cant figure this out. I think the injectors are the culprit but want to see what others think.

Seems like the injectors r dumping so much fuel it is cooling the sensor off causing it not to read properly. Was gonna try moving the sensor down stream slightly.

I had a similar problem with a TBI.

Changing to a GM MAP resolved half my problem.

I installed a 55lb injector (modified 2.5) then stepped down to a 50lbs.



May want to look at your MAP.

Thats actually the only sensor i havent changed. This thing has 230k on the odometer. I will check into that tomorrow.

If yours has a line to it............check the line and the port at the TB, could be clogged.

Jeep Driver said:

If yours has a line to it............check the line and the port at the TB, could be clogged.

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That line has to be perfect.

Also, the engine dipstick tube stud is where the major grounds go for the fuel injection system.
If they aren't attached to a bare metal/clean and shiny spot, you will have issues.

Ill go ahead and change that line. I still need to back probe the sensor. Been crazy busy at work fixing all these wranglers. Hopefully I will get to it tonight

Ok put the scanner on the jeep last night and eveything looks good with the map sensor. 4.8v with key on and 1.9v at idle. O2 will not drop below 3.4v. I even tried inducing a giant vaccum leak but the sensor stayed the same. Im gonna pick up a new sensor again and try that

cwyman6 said:

Ok put the scanner on the jeep last night and eveything looks good with the map sensor. 4.8v with key on and 1.9v at idle. O2 will not drop below 3.4v. I even tried inducing a giant vaccum leak but the sensor stayed the same. Im gonna pick up a new sensor again and try that

Click to expand...

Have you checked for power at the O2 sensor heater leads?

Black is ground. Orange is 12 volts

Make sure the harness isn't melted where it goes from the front of the manifold down to the side of the block.

I have a good 13.6v at the sensor when running

cwyman6 said:

I have a good 13.6v at the sensor when running

Click to expand...

Okay. How many ohms resistance at the black wire to ground?

Also, with the harness unplugged, how many ohms resistance from the black wire to orange wire on the sensor side?

You might be over thinking this. You put in new injectors and now it runs rich. What size injector you go with, Renix like smaller injectors. https://youtu.be/dstyjD5Hy9Y

Changed the sensor out with another bosch and it is working correctly. My fuel trim is only 20 but once i get the bored throttle body it will use the extra fuel it has in reserve. I would not have thought i could get 2 bad sensors out of the box but its possible.

Thanks for your help everyone