Auto Repair - Roadshow forum

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someone help before i go crazy!

by r_ealx / February 18, 2008 12:29 AM PST

I have the 97 grand cherokee with 4.0. I have been having problems with intermittent stalling and backfiring. I tried the backing the screws out from the computer. it helped but here's what I have noticed as of recent. When I take the battery cable off for a few seconds to work on something the next day the jeep runs like gold for the first day but then as the computer is resetting itself that is by the second or third day the intermittent stalling continues. Does this mean I need a new computer for it? Or could I get a mechanic to rest the parameters on the computer? Please help!

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Don't Give Up On The Computer
by sunwatcher / February 18, 2008 7:06 AM PST

The computer is probably fine, but it gets information about how well your vehicle is running from the O2 sensor(s). That would be the first thing I would check based on your description of the problem. If you have a bad sensor, the computer won't be getting information about the fuel/air mixture, and won't be able to adjust the engine accordingly. Some vehicles have just one, while others have multiple sensors. The O2 sensors will wear out over time, so if you haven't had yours checked or replaced in the last couple of years, now would be a good time to do it.

A mechanic will be able to attach a diagnostic tool to your computer and tell you if the O2 sensor is bad, among other things. Make sure you take it to a reputable mechanic, though.

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o2 sensors
by r_ealx / February 19, 2008 1:07 AM PST

that makes sense.. it codes as 21 when I do the key thing three times. is there a way to tell which one is bad without going to a stealership? there is one before the cat converter and one after. I am trying to save some money due to the fact that I also have to replace the windshield before getting it inspected.

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Free Diagnostics
by sunwatcher / February 19, 2008 8:17 PM PST
In reply to: o2 sensors

Some mechanics will do a free diagnostic with a code reader attached to your vehicle. Not sure what the code 21 is, but that might give you a clue as to which sensor it is. I don't believe there is another way to check the sensor without specialized equipment. Once you find the bad sensor, it's a pretty simple process to replace it yourself with basic tools. If you can afford it, it might be worthwhile to just replace both sensors at the same time anyway.

Be warned, a diagnostic might reveal other problems that might need to be fixed as well.

Hope this helps you out.

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i think i found it :)
by r_ealx / February 27, 2008 2:37 AM PST
In reply to: Free Diagnostics

Over the weekend i changed out both o2 sensors. the funny thing was when i went to connect the plugs from the new sensor to the old harness I noticed something odd. on the old harness/plug there are 4 metal rods sticking up that push into the new sensor plug. one of the rods was barely visible and was off the bracket that held it in. I snapped it back into place. After plugging everything back up it has been 4 days with no problems and no check engine light!

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Good Work!
by sunwatcher / February 27, 2008 8:35 AM PST
In reply to: i think i found it :)

That rod would probably be something that could be easily overlooked, even by a mechanic. Great job in finding it! Hopefully you fixed the problem for good now. Grin

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