Wrong O2 Sensor?

[nostopin]

(this is over a period of about 6-8 months) To keep a long story short, my 93exp started running like crap and went from 20+ mpg to 14. just changed the plugs and wires 2 months prior. I thought it was a plugged cat so I cut the bottoms out of them and took the stuff out, then welded the bottoms back on (cant get the cats unbolted from the Y pipe) Ran good, but still bad Mpg. Checked for vac leaks and found none (sprayed ether while running and got no hits on the vac lines) took it to a shop and hooked up the OBD1. dude said it was something wrong with the EGR valve, cant pin point it, but something with that system is bad. So I replaced the EGR valve and got no improvement. just last week I changed the plugs, wires, and O2 sensors. (plugs had white burnt crap built up on them) The replacement O2 sensors were cheap ones from Rockauto, they looked a lil bit different and had a black plug instead of white like the harness and the plugs on the old O2s. it ran like hot garbage for about 30 min after I changed them, but then cleared up. still only getting 14mpg.

OH and the exhaust has smelled BAD when i decelerate or come down a long grade this whole time. Do the plug colors matter on these O2 sensors? Got some electrical contact cleaner and will clean the MAF and all the plug connections I can with 1 spray can and report back any findings

 

[Roadrunner777]

There has to be some backpressure... I have read a lot of threads where cutting out the cats start new issues.

 

[nostopin]

that does make sense. I had a moped that ran like chit when the air cleaner cover fell off. it was designed to run with certain amount of air going in and out. if you change either value it dont like it. so its prob along the same lines with this ford. its intended to run with more back pressure, except now I cant just turn some adjustment screws to correct it. But this makes me question those who have aftermarket intakes and exhaust systems. Any of you out there delete your cats and have a similar problem? I would imagine to get optimal MPG either all the systems have to be working, or they ALL have to be bypassed/deleted, but how do you tell the computer things are there and working when they are not? I will be the last owner of this rig (she's been hammered into the ground pretty hard) so I dont have to worry about getting it smogged again.