ok my dads ol' 89 has been gettin bout 5 mpg on the trails lately . i have since noticed a gassy smell comin from the exhaust . I also hear a hissing sound coming from the fuel rail area, which i think is a vaccum leak. So my question is could this be a cracked header or a bad o2 sensor? Or id there another possibility?
And what color should the o2 sensor be?

 

Check for a vacuum leak first. Especially the MAP, it's bolted to the firewall and has a line that comes down and connects to the side of the throttle body I believe. But yes 02 can cause a loss of gas mileage if it's old it probrably should be replaced anyways.

 

If you do get a new o2 I suggest a OEM part from the dealer. It's more expensive but worth it in my opinion.

 

Aight
thanks but we also did an injector replacement, we just replaced 1, is there an ecu on an 89 that maybe needs to be reset?
FYI the bad gas mileage and air sound started after the injector swap

 

Check to see if a leak was caused while doing the other work... Sounds like raw fuel...