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Discussion Starter · #1 ·
My 85 CJ7, 258 with the POS Carter, doesn't want to idle too much lately. I used to think that I had the only Carter carb without a problem, but I guess the odds of that finally caught up to me.
About a month ago, I was up at Paragon and after running good most of the day, it started to stall every time I got off the gas. I noticed a disconnected wire under the hood on the driver's side, but because it was night, I couldn't find where it had disconnected from. The next morning, I still couldn't find it, so I ran the trails again and then went home, still stalling frequently. I finally tracked the wire down to the O2 sensor. The wire coming from the O2 sensor had neatly tucked itself behind the EGR and that's why I couldn't find the other end before. I put a new wire terminal on the ends and reconnected them, but it still isn't running worth a damn.
With the engine running, looking down into the carb, I can see that the meterng pin is stationary, it should move back and forth. From what I read, this could mean that the stepper motor, O2 sensor or the computer is dead.

My question is:
Would the O2 sensor be damaged by the disconnected wire grounding out against the engine or body?
Would the computer be damaged by the other end of the wire grounding out?

I am looking for a MC2100, but I'd like to get this running in the mean time. I already have a MSD ignition, but I still need to do the distributor cap conversion.

Thanks,
John

85CJ7, 258-six, auto, 4" Skyjacker lift, 4:10 gears with rear Detroit Softlocker & front Lockright, B&M Megashifter, 35x12.50 Goodyear MT/Rs, MSD ignition.
 
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Discussion Starter · #2 ·
I can empathize with you , John . Here is what my understanding is ( though I am not an expert ) :
I do not believe that the disconnected O2 wire would cause electrical problems for the MCU nor for itself . My belief is that it is supposed to send a voltage signal to the MCU , so lack of signal voltage from the O2 sensor to the MCU would be interpreted by the MCU as just part of the too lean / too rich oscillation in the exhaust . I do not believe that the O2 sensor would electrocute itself through self grounding. The lack of oscillating stepper motor pins would tie into the lack of too lean/too rich signal cycles from the O2 sensor. The computer has probably forced the metering pins into the position corresponding with " no voltage received from the O2 sensor " . Until the MCU receives a voltage signal ( from the O2 sensor input wiring) telling it to move the metering pins to the opposite direction of where they are now , the pins will remain fixed . This is my weekend tinkering judgement .

 

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For openers, you need to solder the wires together. The O2 sensor works on very low voltage and a crimp type connector is not going to make it.

I am not familiar with the Jeep system, I have a tuned port Chevy in mine, but they operate pretty much the same. The loose wire ends grounding out would not likely harm the ECM or the sensor. Without the sensor, the system would not go into closed loop though. If the system was running rich in open loop mode, then the O2 sensor could become fouled and may have to be replaced.

Get a book that tells you how to retrieve the trouble codes, the '84 thru '86 have self-diagnosis meaning you can get the codes without a scanner.


 
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Discussion Starter · #4 ·
Thanks for the help.
I guess my first step will be to pull the O2 sensor and see if it looks fouled. I was hoping to nail down the non-functioning part before buying new parts. The O2 sensor is only about a year old. I'll also fix the wire connection.

I didn't realize that the diagnostic system would actually yield any answers. I didn't think that an 85 would have that capacity. Does anyone know how to pull the codes and is there an online source for the meanings to the codes?


John

85CJ7, 258-six, auto, 4" Skyjacker lift, 4:10 gears with rear Detroit Softlocker & front Lockright, B&M Megashifter, 35x12.50 Goodyear MT/Rs, MSD ignition.
 

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If I remember right, you can low-tech test the O2 sensor like this.

1. Remove the O2 sensor from the vehicle.
2. Hook an ohm tester to the two wires comming from the O2 sensor.
3. Use a small propane torch to heat the end of the sensor that goes in the exhaust pipe.
4. Watch for a rise or fall in Ohm value.

I am not sure which wires you should test on a 3 wire sensor but maybe someone else does?

Trailhed.com
 

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A three wire sensor is heated... and more difficult to test.

On the Carter BBD equiped Jeep there are no recoverable computer codes. The diags plugs on the fender just let you exersize parts of the emissions system through the computer. This tells you if the comptuer circuit or the device being exersiszed is good, or bad.

 

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In reply to:

You can't actually pull computer "Codes",
Could well be, I missed the part in the information I had that said 4-cylinder and V6. Sorry.

 

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Like has been said, when the MCU doesn't receive a signal from the o2 sensor, the computer goes into open loop operation. This means that the metering pins will remain stuck in their last position before the o2 sensor came unconnected which is probably why you kept stalling.

I think your sensor should be fine assuming it was operating properly before it came unconnected. As far as I remember, the o2 sensor on my 84 258 only has one wire coming out of it, so all you can really do to see if it's working is hook up a voltage guage and make sure it's generating a low level of voltage. For some reason, you can't check it at the diagnostic plugs.

TEXAS1AL

84 CJ-7; 258 I6; Restored-to-Stock Condition
 
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Discussion Starter · #10 ·
Here is a bit more for your puzzle :
metering pins at rear ( firewall side ) = Lean position
metering pins at front ( radiator side) = Rich position. This info is per YJ Service Manual , P. B-283.
When you manually choke off the air supply from the butterfly area, this should cause the engine to run rich . In response to running rich , the MCU should tell the stepper motor pins to move to the LEAN firewall position , trying to lean the mixture in response to the richness caused by choking off the air supply. The MCU is supposed to have already received input from the O2 sensor saying " too rich in the exhaust " . The O2 sensor does this by sending a higher voltage ( greater than 0.6 volts) to MCU ( per page B-282). Hope this can assist you . I can not comment regarding the fouling of the O2 sensor by a too rich exhaust . I wish that I knew if this were possible. It might explain a "sensitivity lacking "by the O2 sensor , thus providing bad input data to the MCU. Any experts to comment?

 
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