say guys i got a question so my car right now has the engine light on, i got it checked and its reading 1) all 4 o2 sensors (which im sure its why im getting such bad gas millage) 2) something with the egr and 3) something with the emissions solenoid. im getting my hands on the front 2 o2 sensors tomorrow. so i went under to take to get them off and i saw that the exhaust pipe from where the flange hooks up to the manifold had one of those aluminum pipes that you can get from autozone welded im place of the front 2 cats. (i think if im right the 04 mustang had 4 cats) it has the back 2 cats but they ripped me off for the front 2. so my question is would it be a good idea to replace the front 2 o2 sensors right now and the back 2 say next pay check, and if i do just replace just the 2 would they go bad right away cuz of the missing cats. or should i wait and replace the cats first and then wait and replace all 4 o2's together? also with the cats missing should i even replace them at all or am i just wasting my time and i should get the cats first and then see about replacing the o2's

 

Do all four at once. The first two sensors are upstream from the precats, so they'll be fine. However, your rear (downstream) sensors will clog sooner due to lack of proper emissions controls.

 

well the codes read all 4 o2's, so if i get what your saying the front 2 would be ok but the back two would clog. but since the back 2 are already clogged up then i should be able to replace the front 2 and leave the back 2 on and replace them next check shouldnt i? with out the front 2 getting clogged?

 

so i got the money together and ima put in all 4 o2's now as far as me missing the front two cats will the oxy sensors clog up prematurely or will i be able to ge the same time use out of them as i would with all four cats?

 

If the two downstream don't work right, they'll mess up your A/F ratio... causing poor MPG and the motor will kick out a lot of crap, clogging up the two upstream in no time at all.

 

so i changed out all 4 O2 sensors yesterday when out and did a run and no engine light came on. this morning when i got in to go to work it came on as soon as i turned the key. i went and got it checked again and it gave me the codes for all 4 sensors again. what could be the proble im having, i got 4 new o2's and i ran it maybe 15 just around my neighberhood for maybe 5 miles or so. anyone know what it could be???