Ok, I will say it again, GET THE CODES PULLED! Otherwise it is a shot in the dark. The PCM controls more than emissions, it controls the whole motor. Instead of going with a gut feeling, get the codes pulled at Autozone, Parts America, ect (they do it for free) write them down and bring them here, we can then go from there.

 

My '93 4.0 has one by the cat.

If you change it, use patience. Hit it with Liquid Wrench (LW) or equivalent. It's too cramped to get my O2 sensor tool on it so I used a wrench and tapped it with a hammer. It took a few cycles of tapping and LW.

BTW, the Bosch part is a 22mm nut size.

 

one would thing that the Aero engineers would have put the O2 sensors on the side of the pipe or a least 45d down instead of directly on the top.
Not all Aero drivers are crazy like me and drive thru 18" of snow heading for that perfect snow camping spot or winter photo.
Haven't torn anything off the bottom yet but have come close, few large boulder dings and comalong pulls out of holes.

 

focusyn:
have the tranny shop check or you check the O2 sensor wire plugs, they may have accidently unplugged an O2 sensor when overhauling tranny.

 

I have a code reader, haven't had the chance to pull the codes. The CEL was coming on intermittently before they overhauled the tranny. I think the problem will be solved this weekend, haven't had time lately.

 

I tried to change mine. So far no luck. This thing is tight! Bad thing is that the wrench is chewing up the bolt I guess I need to soak it a little bit longer before tackling it again.

 

When I changed mine earlier this week, I couldn't budge it with a 22mm end wrench, but it came right out with a pipe wrench and a gentle persuader bar (4' iron pipe). I had to pull on the bar from the driver side of the vehicle. Be gentle!

 

wrap a rag around it soaked with penetrating oil overnight, then do the 6 point box end wrench and hammer tapping, factory doesn't bother with anti seize, time is money and they will never see it again.

 

I personally prefer the gentle approach of a huge pipe wrench advocated by DracoScott

 

I couldn't get the box end wrench on the sensor, the wiring connector wouldn't fit through it. I was tempted to clip the wire, but I'm gald I didn't, as it turned out, I had to reinstall the sensor so I could run to the store and get the right one.

I'm headed off to Atlanta for the weekend, and will be able to evaluate mpg with the new O2 sensors.

 

Ran the code scanner. Wound up with HEGO bank 1 indicates rich and another code for the same sensor indicates lean. Sounds like a bad O2 sensor is the culprit.

 

focusyn:
time for the "Big Hammer" pipe wrench, works every time, the Aero sees it coming and gives up.

 

guess I need a bigger hammer, either that or my aero is just more determined. seems like it never just gives up. think we should get some sort of recognition through ASE for just getting near an aero with tools in hand. lol

 

Replaced O2 sensor... twice. First one was apparently defective, second one seems to have the van back to its old self again.

Didn't have to use much force either. Of course, I soaked it overnight in Corrosion X (www.corrosionx.com). The stuff works better then my old favorite, PB Blaster or WD40. It's more expensive, but you have to use less of it. The Rejex paint protectant they sell works pretty good too.

Corrosion X helped remove the original shocks from their mounts with little fighting or rounding of the nuts.

 

My uncle has a friend with a garage, he won't touch the Aero. I've heard other stories of that happening too.