Running rough

[PMC]

Hi, I just bought a 1994 Ranger XLT 4x4. It has a manual transmission. When I bought it it ran a little rough but I smelt gas in the exhaust. So I figured it was the O2 sensor. I replaced it with a premium Bosch sensor. It ran great right away, and about a day or two after, it started to run a little rough again. but this time no gas smell. It sounds like it sucks air and not getting enough fuel. It even backfired a couple times, not the bang but a pop. I am not a car mechanic but I am a small engine mechanic. I would like to do the work myself but I don't know where to start. Could someone help me? What could this problem be? And what's the cheapest fix that I could do?

 

[locovaca]

Start with the simple stuff. Look for a vacuum leak- check of all of the hoses hooked to the intake and follow them to their end. Being a 94 rubber is going to be rotting out. Especially check the evap system hoses. It will go from the intake, to the purge solenoid, to the charcoal canister, then all the way back to the fuel tank. I know my 93 had several sections along that route that were dry rotted.

You may also want to check timing, although you said it ran ok for a while it probably isn't it, but it won't hurt.

Also, if you didn't reset the computer after installing the new O2 I would do so. Unhook the battery for a few minutes. This will make the computer re-learn the operating ranges of the sensors. If you had a bad O2 it would've skewed the learned "normal" values.