Hey guys i am new to this forum and i have done a search trying to find the cause of my problem with no luck yet so i am going to start a new thread to try and find the cause. I have a 1990 bronco II with 112,000 original miles on the original everything. 2.9L automatic 4X4. I fist failed my smog test and they replaced the O2sensor ground wire and the main case ground wire. After that I passed california smog in September 2010. Although it passed smog my gas mileage is poop, aprox 11 miles per gallon. I am only getting between 275 and 300 miles out of a 25 gallon tank. I previously had an '89 bronco II and i was getting 17 - 21 miles per gallon. Within the last couple weeks the check engine light comes on after about an hour of driving and then if i shut the truck off right away and turn it back on the light is gone. Also the light will randomly turn it self off if driven for a while longer. I pulled a code using one of the digital OBDI code readers from Orielly auto parts. Following all of there instructions i was able to pull code 41 for the KOEO continuous memory and then code 41 also in the KOER test. The book describe the code as HEGO (HO2S) sensor signal out of range / always lean and; HEGO (HO2S) sensor voltage low / system lean. Can anyone tell me what sensor is bad or how to test them and how to improve my mileage? The O2 sensor was changed last year also. In my reading i have read such problems as the TPS sensor being bad, the fuel pressure regulator being bad, the O2 sensor being bad, or the MAF sensor being bad. If anyone can help pinpoint my problem i would be grateful. Thank you

 

Lean O2 sensor codes can be among the more difficult to diagnose by the book. Basically, anything that can cause the engine to run lean can cause a lean code. A few ideas:

Some people consider the O2 sensor a maintenance item. If the O2 sensor has more than ~50k miles, you might consider just replacing the O2 sensor, clearing the codes, and see if that resolves the issue.

By the book, the usual first check is to test fuel pressure with a fuel pressure gauge to make sure the fuel system is operating at spec.