i kinda have the same problem from my 1990 cadillac eldorado 4.5L PFI engine it will run like crap then all of the sudden run perfect and messup again i am getting upto 34mpg running about 60-72mph no problem when it runs fine well i changed plugs/wires and the did nothing changed my cap and rotor ...nothing coil.. still nothing has a miss to it and seems as tho one of my injectors are out i started upiing sparkplug wires to find which cylinder was out and figured out it was #8 so i pulled the wore off the injector and miss continued the exact same which confired the cyldiner being dead well i hooked a test light up (12V) and no light or nothing i have heard it could be the o2 sensor... could this be true? or what else would i be looking at in the way of problems because when it does that i drop my avg mpg signifigantly such as down to 15 mpg and maxing at 22-23 highway and as low as 17 and with being EXTREMELY tight on money as is i cant spend more then i need to so any help at all is appreciated thank you very much
Dave