My 91 740 with 154k miles (Regina) has gieven me 20-22 mpg for the last eight years. I read where the O2 sensor should be replaced periodically...I believe 60k?...The only problem im having is a slight engine knock with regular gas down here in S.FLA. Premium sees to take of that..Would it harm to replace the 16 year old O2 sensor?

Beware of general information in regards to O2 sensors when it comes to your Regina. Common knowledge about sensors getting lazy, and needing to be replaced after 60K, etc are based on the common O2 sensors.

Most cars use a "zirconia" sensor which generates voltage based on what's going on in the exhaust stream. Regina, and some Jeeps and Nissans, use a "titania" sensor which changes resistance instead. Titania sensors seem to be much more long lived (maybe because they don't need to be open to the outside air for reference like zirconia). My two Regina cars both have old and likely original sensors at 240 and 205K miles. I bought the $100 spare as Lucid smartly recommends, but haven't put it in yet since I still get 24mpg in the Summer and 21 in the Winter here in Minnesota with 87 octane gas that is 10% ethanol year round.

chuffsy,

...The only problem im having is a slight engine knock with regular gas...

With 154K miles, I would suspect this is caused by carbon buildup. Try running a bottle of Techron or other cleaner through with each tank of gas. After three or four tanks, try the mid-grade gas and see if it still knocks.

Do you "baby" the car? In conjunction with the fuel additive, run the RPM up a little higher than you would normally.

I doubt a 16 year old O2 sensor is doing much of anything any more. If anything, it is signaling a constant lean condition, causing the ECU to enrich the mix, causing more carbon buildup. Yes, do replace the O2 sensor. You will probably see a better MPG as a result.

Is the timing belt recent? Plugs, cap, wires, etc? It may be time for good tuneup.


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Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 51 year old fat man ;-) -- KD5QBL

... is at Sparkplugs.com. Click the Applications FIND! button and you'll see your car listed.

NOTE: The sensor plug pictured (round) at the site aboveis an error. My sensor came with the correct 2-pin (flat/rectangular) plug.

I believe the price is still $99.85 + shipping. This is the same NGK sensor that sells elsewhere as a repackaged "Walker" brand for about $135+ shipping.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

That's where I got mine for my 90 740 GL (Regina), it plugged right in to the stock harness.

Of course, I just stopped by Midas and paid them 20 bucks to put it in for me. I hate working on exhausts. LOL.

Getting it out of the exhaust system may prove to be 'interesting' but , No, it wont hurt anything. you may find the new one to be more responsive and thereby save you some gas
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm