BlueRidgeMark

What is a normal voltage for the 02 sensor?

I've had a plethora of problems with my 97 Country lately. It started many months ago with a sudden stuttering on my commute home. It would come and go like flipping a switch. At one point, I pulled the O2 heater fuse and replaced it, and that seemed to clear it up for a while. Then it came back, intermittently.

Then it just died one day and would not restart. I had it towed to my regular shop. They replaced the PCM. I drove it home with no problem (about 30 minutes). The next day it died as I left my driveway.

This time I had it towed to the local Jeep dealership. I figured they had to have better resources and maybe deeper expertise than my usual shop. They found the distributor shaft [bushings? bearings?] were shot, allowing the distributor shaft to wipe out the cam position sensor. Both were replaced, and all seemed well. It ran, but a bit rough, like it has been.

The next day I got about a half hour down the road toward work, and it shut off like switching off a light. Towed back to the dealership. They spent quite a lot of time on it, and finally concluded it was the PCM. Replaced under warranty, with good cooperation with my regular shop.

That was last Thursday, and it's been fine since then, but still, a bit rough.

This evening it started bucking quite a bit, again, like flipping a switch. Sometimes fine, sometimes rough. I plugged in my Bluetooth OBDII reader and fired up Torque to see what was happening.

Here's what I have:

Fuel trim runs in the 20-35% range when it's running rough. Down in the teens and even below 0% (how does that work?) when it's running fine.

02 sensor voltage runs from 0-2 volts, and it sorta seems to correlate with the running rough when it's higher, but then, most of the time it was at the 2 volt point. Or was that .02 volts?

Codes are the usual suspects for misfires: P0301, and random cylinders.

Also a P0171 and a P1294.


Here's the skinny on the P1294:

The P0171 is another new one to me:

So, two codes pointing to a vacuum leak, and the behavior suggests it's an intermittent leak. Probably not related to the PCM issues.


But do I have an 02 sensor problem as well? What's a normal reading?

eignub

It will vary greatly from what i understand. I use torque also, but gave up on trying to get an o2 voltage reading from it because it jumps around. a real easy step you could do would be check your iac valve. mine was running a little rough, and after cleaning that it helped. it shouldnt throw a code, but its something that should be done semi regularly anyways.

BlueRidgeMark

Yeah, I'm not really happy with Torque. I can't get it to give me any logs, and their website is a MESS. I can't find out if emailing logs is a Premium feature that doesn't work in the free version, or if I just have a problem with mine. I don't want to spend even the small amount for the paid version because the web site is such a kluge.

I saw a post here recently with a screenshot that looked pretty good, but I don't know what app he's using.

t.mcginley.jr

Narrowband O2 sensors (basically regular ones, not widebands) operate on 0-1 volts. Closer to 1 volt is rich, closer to 0 is lean, it should fluctuate between 0 and 1 constantly as its running. ECU regulates air-fuel ratio using these readings, along with engine temp, intake temp, etc.

Fuel trims should be under 10%, but under 5% would be better. This means it's adding fuel. If it goes negative (which is normal) is subtracting fuel. Short-term fuel trim (STFT) constantly moves as its running to try and keep a good A/F ratio. Long-term fuel trim (LTFT) is like a baseline average that the ECU learns over time. For example after running for a few days time, the ECU knows that your particular engine runs good if LTFT is 1%. It will then always add 1% more fuel than the programmed baseline. But say one day its cold or hot outside, then it uses the STFT to adjust on the fly.

From your problems, sounds like its running really rich to compensate for too much air. Usually this is from a vacuum leak or bad MAP/MAF sensor. Inspect vacuum lines, intake tubing, etc.

bigbadon

All those fancy dials slow your response time. A better free app is "piston' no fancy displays but lots of real time data.