Ok, well I was talking to my grandpa( he owned the truck for the last 20 years) and I asked him if he'd ever changed the o2 sensorr out and he said he hadn't ever touched it or even thought about it. As of right now I get around 13 mpgs( I dp have a lead foot and like to hear the glasspacks talkin) but this seems a little low. Its a 5.0 with like 183xxx miles. How big of a difference would the new sensor make and can any1 tell mee exactly which one I need. I looked on autozones website and they had a lot of diff ones. Its a 90 with a 5.0 and e4od if that matters. It seems like it runs rich judgin by smell but I don't have any cats either so idk.

 

It shouldn't smell rich even with no cat. Ymeski says he changes his O2 every so often because they switch slower when old. It sure wouldn't hurt.

 

i think the NGK brand ones are good.

 

Switch speed slows & accuracy degrades. !00K should be max no matter what. 60K is prudent. 35k will continue to maximize MPG.

Running rich, carbons up the combustion chambers. So do the seafoam treatment first. Make sure your at operating temp.
https://www.f150forum.com/f33/how-se...-1991-a-31505/

I believe Motorcraft's O2 sensor is a private labeled Bosch product.

May want to do a fuel pressure test ,also checking pressure bleed down time to make sure the Fuel pressure regulator is working ok & injectors aren't hanging.

I agree w/ "JCMS" re: the smell. The CAT isn't designed to deal w/ that much residual fuel, & your problem is upstream of where your Cat used to be.

 

Wellit definitely hasn't been changed in about 170k miles or so, so I guess ill do that this week then, how do you do a fuel pressure test( I know a probably stupid question but I'm only 16 and just getting into this stuff). Also I just got an oil change not to long ago, should I put the seafom in the oil or not? I ran some through it about the beginnning of the year.
I know this is a lot of questions but I want to get the truck running the way its supposed to.

 

run seafoam in your oil about 100 miles before you change it.

 

You need a fuel injection fuel pressure gauge, and you hook it to the test port on the fuel rail.

 

Ok, about hw much pressure should I be expecting? And thanks for all the answers.

 

35-45 engine off, 30-45 engine running increasing 5-10 with regulator vacuum disconnected.