Ever striving to improve gas mileage, (I get 13-15 mpg in town and 17-19 mpg highway), I decided to change the oxygen sensors on my , '96 AWD, 4L. It's got 126,000 miles and I suspect that the sensors have never been changed.

Yesterday, I went to Autozone and their computer says I need one downstream (bosch 15717) and 2 upstream (bosch 15718) the cat. Unfortunately, they didn't have the 2 upstream units in stock. I got the one downstream and headed across the street to Advance. Their computer showed only one needed for upstream, (bosch 15718), which they did have in stock, so I got it too. Looking under the vehicle, I can easily see the downstream sensor and it looks like not a problem to change, although the wire connector maybe harder to find. Likewise, I can see only one upstream sensor. It also looks easy to unscrew and remove.

So who's right? Is there a second upstream sensor that I can't see? Where is it? Any tips on changing these out would be appreciated.

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Noper, those are the only two O2s on the 4.0 Aero.

Rule of thumb, never believe the guy behind the parts counter (unless it is me. )

 

I replaced the upstream, 15718, near the oil filter, but where is the downstream unit located? If you've replaced yours, pass on any tips on how to. Thanks!

 

Only the later models have a downstream O2 sensor. Mine is a '95 and it only has one O2 sensor, before the cat.

Regards

 

If there is a problem with the sensor, shouldn't the check engine light come on?

 

No, not always, especially with the older cars. Mine went for a long time with a bad O2 sensor and no warning. The system just goes rich and foul up the plugs.

 

So then it's a maintenance item? Gee, maybe I should replace mine. It probably has never been changed.

 

I learned my lesson. I change it now every 60K miles. For the Aerostars that isn't too bad, about $50. Cheaper on the knuckles than changing the plugs

 

It is located just past the second cat. It is alot easier to remove than the one by the oil filter.

 

Same question, except for a 93 3.0 liter. Does the 3.0 have more then two O2 sensors? I took the van out for it's maiden voyage after the tranny was rebuilt. Tranny shifts fine, but the van lacks any power above 60 mph ( I know, it's not a rocket, but it used to do better) I get an occasional CEL if I run hard ( climbing a hill or highway driving for extended periods) but it goes away and comes back. CEL was happening before tranny went, but I didn't notice mileage being THAT bad.

Loose wire, or bad 02 sensors? Right now, I am only averaging 16 mpg for mostly highway driving. I was getting over 20 on the highway. I'm thinking 02 sensor.

 

As a general rule, anything 96 and newer (OBD-II) has at least one sensor upstream of the cat, and at least one behind the cat.

 

focusyn

what is CEL code?
is the new tranny shifting into OD and can u tell if it's going into torque converter lockup which is not as noticible? either not working, major effect on gas mileage.

depending on what was replaced in auto tranny, full master rebuild-all clutch packs, torque converter, bushings, bearings etc, turning resistance will be higher until broke in.
if just a quicky band-clutch disk replace, then you have other problems than auto.
take back to tranny shop and get the problem on record.

 

'93 3.0L has only one O2 sensor.

 

The CE light turns on when there is a code. It could be one of numeruos problems. The PCM does not just monitor the O2 sensors, it monitors all of the engine functions. Get the codes read ASAP!

 

Sorry, CEL is Check Engine Light. Tranny shifts fine and is going into OD and locking up torque converter.

I was thinking that new tranny parts might have something to do with it, but I am pretty sure it's the oxygen sensor or something to do with emissions.