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Old 12-16-2011, 23:45   #1 (permalink)
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O2 Sensor Replacement

The wife has been driving around 140 miles a day, and she's racked up some miles on the GM already. It's averaging around a high 23 mpg, and 90% of that is highway driving. Even though I'm happy with the results, there is always room for improvement!

So, one question I have, is about when is a good time to replace the O2 sensors? The car has 95k on it now. I've been told that the rule of thumb is change them around 100k. Correct? Looking at the parts on Rock Auto, it seems that there are two upstream, and two downstream. I was also told that the upstream ones do most of the work, and should be the ones to get replaced. Also correct? Again, looking at Rock Auto, which brands are the better one's to get? And, are these relatively easy to replace? I don't have the sockets with the slit in them (for the wires), so it will have to be regular wrenches for me. Anyone know the size I need?

Also, since I'm here, I responded to another thread someone started about spark plug replacement. Since I'm going to 'tune it up', I was thinking of trying E3 plugs. Anyone tried them yet? I'm curious what the results were.

I'm just trying to squeeze as much mpg's as possible out if it! I am amazed that I'm even getting almost mid 20's, as my '77 LTD (without overdrive), is lucky to get half of the GM! And, the LTD is only 7" longer in wheelbase than the GM!

Thanks,
John
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Old 12-17-2011, 10:06   #2 (permalink)
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Re: O2 Sensor Replacement

There is a test with a high-impedance digital volt-ohm meter that tells how well they are working. Without one, I'd only replace the front ones. They control the fuel mixture and I'd get the Motorcraft or Bosch. The size wrench you need is 7/8" or 22mm.
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Old 12-17-2011, 17:18   #3 (permalink)
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Re: O2 Sensor Replacement

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There is a test with a high-impedance digital volt-ohm meter that tells how well they are working. Without one, I'd only replace the front ones. They control the fuel mixture and I'd get the Motorcraft or Bosch. The size wrench you need is 7/8" or 22mm.
Thanks, Bert. I do have an AutoXRay 6000 scan tool, that does engine data monitoring while running. Is there anything I can look for, to see if they are getting weak? Plus, how hard are the front ones to replace?

John
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Old 12-17-2011, 20:59   #4 (permalink)
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Re: O2 Sensor Replacement

Rev up the engine to around or above 2000 rpm for the sensor to get heated up and oworking. The readings for the sensors should keep on bouncing above and below 0.45 V rapidly. If the engine has been clean burning, (oil serviced reularly and not using oil) the sensors may still be working properly.
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Old 12-18-2011, 07:35   #5 (permalink)
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Re: O2 Sensor Replacement

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Rev up the engine to around or above 2000 rpm for the sensor to get heated up and oworking. The readings for the sensors should keep on bouncing above and below 0.45 V rapidly. If the engine has been clean burning, (oil serviced reularly and not using oil) the sensors may still be working properly.
Thanks, I'll try that when she gets home, then the engine will be warm.

It's funny you say about the engine using oil, as it seems that this one does a little. It will go down rather quickly a half a quart, then kind of stay there a while. Is that common with these? I know a lot of engines will find the oil level they like, and stay there. Eventually though, it will go down to a quart low. Is this something I have to worry about? There are no spots on the garage floor, and I haven't noticed any blue smoke out the exhaust.

John
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Old 12-18-2011, 08:40   #6 (permalink)
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Re: O2 Sensor Replacement

Possibly valve seals. The 95 and older had a poor design and would use quite a bit of oil at around 100,000 miles. Replacing them with the new type made them last a LOT longer. Most engines will start to use a little oil as the mileage adds up.
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Old 12-18-2011, 10:30   #7 (permalink)
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Re: O2 Sensor Replacement

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Possibly valve seals. The 95 and older had a poor design and would use quite a bit of oil at around 100,000 miles. Replacing them with the new type made them last a LOT longer. Most engines will start to use a little oil as the mileage adds up.
You said '95 and older, but this is a 2000. So, this should have the 'new design', right? I also think this engine might be pretty dirty, and I didn't flush it when I bought it. I think I will, at the next oil change. I did just change the filter, and it was fine for a while, but I think the filter might be getting filled up with gunk, as the Amsoil is cleaning it out. I will have to wait a while before I change oil, as there's only 11K on the oil now, and only 1K on the new filter.

John
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Old 12-18-2011, 11:16   #8 (permalink)
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Re: O2 Sensor Replacement

I knew you had a 2000, I was just infering to the fact that valve seals do wear out but the older ones did sooner. The newer ones wore quicker when serviced poorly and that goes for rings and other parts as well.
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Old 12-19-2011, 21:03   #9 (permalink)
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Re: O2 Sensor Replacement

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Originally Posted by Bert View Post
Rev up the engine to around or above 2000 rpm for the sensor to get heated up and oworking. The readings for the sensors should keep on bouncing above and below 0.45 V rapidly. If the engine has been clean burning, (oil serviced reularly and not using oil) the sensors may still be working properly.
Bert,

I was able to try this, and I think one of them is a little weak. They would both jump up and down, but one of them was at zero for some time, then when it did start to move, would not get as high a number as the other one. For some reason, it was measured in MV, not volts, but the one side would constantly be in the 5-6-700 mv range, and the other one took forever to even get reasonably close, and when it did, got only around the 500 mv range. The car was warm, but was off for a little while, as I was having problems with the scan tool seeing the car. I ended up taking out the 30 amp big fuse (in the block under the hood, by the battery), and putting it back in. The one 'leg' of the fuse seemed to have some corrosion on it, and I believe by pulling it out/putting it back in, got a connection at the OBDII port. Anyway, the car was only off for 15 min max. Before that, it was driven over 70 miles, so I believe it was plenty warmed up! I can't remember what the sequence was now, but I could see all 4 O2 sensors. I believe the ones before the cat were bank 1's, and the one's after the cat were bank 2's.

So, with that senerio I just mentioned, would one of them be a little weak? Does that even happen? I always thought that either they worked, or didn't, but it did seem as if the one was being a little 'lazy'. I orderd 2 from Rock Auto, as they were cheap ($37 ea for Motocraft). I'll be putting them in during X-Mas weekend.

By the way, you never did tell me how hard these are to put in? Are they in a reasonable spot, where you can get a wrench in? Or, will I need the slotted socket?

John
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Old 12-19-2011, 21:38   #10 (permalink)
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Re: O2 Sensor Replacement

That sounds like a weak one. Might as well replace them both. I have to admit, I forgot how hard they were to replace. I' think I just used the wrench but working on so many different vehicles, I get them mixed up. I don't have mine anymore so I can't check it and I semi-retired so I can't look at one that easily. Mine was a 2000 also.
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