when i first start my 90 4.0 it runs bad until it warms up. it hesitates and backfires and chugs bad. i think its my 02sensor but im not sure. im pretty sure my oil pressure gauge is bad too its pegged all the way to the right once its started. any input would be great

 

Your oil gadge may not be bad,check the wires first make surethey are tight,change the sending unit out next.The running bad could be a bad map sensor,IAC sensor,or a vacum leak.

 

I have had some of the same issues before,it can be a worn cap and rotor,it could also be bad compression.
When I have had problems like this the first thing I do is a compression check,even if I am pretty sure it is ok. Reason is as long as it is not mechanical,it is easy to find by testing the other things it can be.
My oil pressure is pegged to the right now,like the previous post said check your wire going to it,I know thw wire is my problem because I bumped it today putting in a new starter relay,just have not repaired it yet,I also have a mechanical guage.

 

i replace the oil pressure sending unit today and now my gauge works. and i swaped my 02 also but didnt really have a change in its bogging down. imma try and find a juk ard and swap to 5.0 injectors and see if thats my problem. i think for some reason its not getting feul. im thinking i might have clogged inectors but idk.

 

Hi also test your tps sensor,mat sensor,and cts any of these can ether cause a rich or lean condition if one or more are bad