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  #1  
Old 08-18-2015, 08:05 AM
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1997 Grand Cherokee O2 sensor troubles

Picked up a very clean 97 GC. 198,000 miles runs great, 17 mpg, no running problems, doesn't even burn oil. Took it on a 1000 mile trip this past weekend, the muffler has been getting worse. When looking at it I noticed the O2 sensor in the cat had all taped up wires and they were broken, also a rot hole which made the O2 sensor fall out. When I got home I replaced the muffler and straight piped the cat, using a bung to install the sensor. After some searching I found vague wiring diagrams for the O2 sensor and jeeps cut harness. Soldered the connections and took out for a drive. Almost no power.... got back, disconnected battery for a minute, took for another drive, better but still a little sluggish. Figured some driving it might get better. Nope. Unhooked the O2 sensor and full power again. Never any CEL lights. So any suggestions as to what might be going on here? Thanks!

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  #2  
Old 08-18-2015, 10:43 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

Welcome to the garage.
Do you have a scanner with live data, to observe the O2 sensor voltage output (changing from 0.2 to 0.8V) and see what the fuel trims do (STFT and LTFT).
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Old 08-18-2015, 10:45 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

I do not. I usually only mess with mechanical diesels. I got this jeep for $400 last fall and it hasn't given me any trouble until I tried fixing it. Haha.
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Old 08-18-2015, 10:48 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

If you have a smartphone, you can buy a cheap bluetooth or a little more expensive wifi dongle from e-bay and install the free Torque app. You can then see and errase faults and monitor many live data.
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Old 08-18-2015, 10:50 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

That's pretty sweet. I'll have to look into it. Any recommended brands? If I've been driving it a while with no issues with the o2 sensor unhooked I figure there would have already been trouble.. or at least a code.
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Old 08-18-2015, 11:31 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

I think they are all made in China.For bluetooth dongle its an ELM 327 dongle. I think they go for around $15.
Is your jeep OBDII by the way, otherwise it will not work i think.
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Old 08-18-2015, 12:02 PM
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Re: 1997 Grand Cherokee O2 sensor troubles

No clue. It's a 97, so should be. I think it was nation wide mandated to go obd2 by 96.
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Old 08-18-2015, 05:23 PM
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Re: 1997 Grand Cherokee O2 sensor troubles

Now I've noticed it cranks about 5 seconds before starting. Never did that before.
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Old 08-18-2015, 06:45 PM
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Re: 1997 Grand Cherokee O2 sensor troubles

If you first prime the fuel system three times before starting, does that make any difference?
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Old 08-18-2015, 06:53 PM
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Re: 1997 Grand Cherokee O2 sensor troubles

I'll try it.
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Old 08-19-2015, 07:43 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

No difference. Like I said there was no issues at all prior to hooking up the o2 sensor in the cat. After I fixed the exhaust and reconnected the wires then it started acting up.
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  #12  
Old 08-19-2015, 08:49 AM
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Re: 1997 Grand Cherokee O2 sensor troubles

Eventhough you had no issues before messing with the O2 sensor, when starting the jeep and when warming up, the O2 sensor output is not used by the PCM, it runs in open loop. After warming up a bit, the O2 sensor reading will be used and it will run in closed loop. Your jeep uses a 4 wire O2 sensor? How many sensor does your jeep have?
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KYB Gas-a-Just shocks / Pirelli Scorpion ATR 245/65/17 - Transgo reprogramming shiftkit.

VW Beetle 2.0 TSI 2013
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