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94' Grand O2 sensor issues


 
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chris21
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Joined: 20 Jun 2005

PostPosted: Mon Jun 20, 2005 3:10 pm    Post subject: 94' Grand O2 sensor issues Reply with quote

I have a 94 grand cherokee with 180k miles. aside from the viscous coupler being completely crap (soon to recieve a 242J transplant), there are issues with the O2 sensor. I recently replaced the sensor after getting a code "21" which I believe is non changing voltage. now a few weeks later i am getting the check engine light (containing code "21" again) usualy, but not always, when i start it up, and it will immediately rev up to around 1500 rpm and then fluctuate between around 1200 and 1600 (resulting in a very rough idle), until i put it in gear at which point it drops back below 1000 where it should be. Other times it starts up just fine, and on some ocasions the light will come on while im cruising at constant highway speed.

Is there anything else in the O2 sensor circuit that could be screwing with the computer, or burning out my O2 sensor? Could my bad VC be putting more strain on the engine that it is expecting and therefore throwing off the calculated fuel/air ratio? I am also considering replacing the plugs and injectors just because they are old, but i cannot think or anything else that could be causing a code "21". any help would be greatly appreciated.

~Chris
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CoreyXJ
Turkish
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Joined: 20 Jan 2004
Location: Louisville, KY

PostPosted: Tue Jun 21, 2005 2:15 am    Post subject: Reply with quote

What exact code is coming up? Is it a PO121 ?
The O2 sensor wouldn't really effect it that dramatically to where it would change the idle. The Idle Air Control (IAC) and Exhaust Gas Recirculation (EGR) has more to do with the idle. The O2 sensor does however control the computers calculated air fuel ratio and changes it as the engine warms up.
Look at the O2 sensor and see how many wires come off of it? 1 or 3 ? You could also take a MultiMeter and measure the voltage coming off of it - this would tell you if you are running rich or lean. The correct voltage for an O2 at operating temp is between 450mV - 550mV. If the voltage is lower than that thenm its running lean and you could have the IAC stuck open... If the voltage is higher then you are running rich and might have some EGR problems (which would explain the rough idle...)

Let us know what all you find out and if anything changes...
CoreyXJ
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"Get busy living, or get busy dying..." - C.W.

"Do what you love to do...the money will eventually follow" - I. Larry
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chris21
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Joined: 20 Jun 2005

PostPosted: Tue Jun 21, 2005 6:39 am    Post subject: Reply with quote

I have no way of retrieving the actual error code from the computer, i can just count the flashes of the check engine light by doing the on, off, on , off, on thing.

I had been getting a code 32 which is a failed EGR system. I took the egr valve off and cleaned it out (was pretty full of carbon) the best i could, but i dont really want to spend the $125.00 on a new one, and i figured it was fixed anyway since i stopeed getting code 32. The sensor itself has 3 wires coming off of it.

Where is the IAC located? Because once while i was having this problem and the engine was reving at like 1500-1600 rpm just sitting there in park, I popped the hood and took off the air intake to see if the throttle was open at all....and it wasn't, so i couldnt figure out where it was getting enough air from to do what it was doing.

Anyway, any help is appriciated

~chris
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chris21
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Joined: 20 Jun 2005

PostPosted: Tue Jun 21, 2005 8:09 am    Post subject: Reply with quote

so i took off the IAC for the hell of it, and it was pretty dirty so i cleaned it and i think that may have helped. Hopefully the crap in there was just holding restricitng the valves motion, and it isnt broke or anything. I will drive on it for a bit and see if anything pops up. thanks
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CoreyXJ
Turkish
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Joined: 20 Jan 2004
Location: Louisville, KY

PostPosted: Tue Jun 21, 2005 1:24 pm    Post subject: Reply with quote

The only thing you have to be careful of when you remove and clean an IAC is that you may break it in the process. Its a stepper motor that just moves back and forth and if you upset its functionality - it no worky!!
So if it idles funny or not at all then you need to replace it. They are about $40-50 at the parts store.
Let us know if it acts up anymore....
CoreyXJ
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"Get busy living, or get busy dying..." - C.W.

"Do what you love to do...the money will eventually follow" - I. Larry
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