1991 2.9 Ranger Code 41 EGO replaced still issues idling, rich, etc..

[Fairlaniac]

My '91 Ranger 2.9 began to run rough, smell rich, surge & dive idle, check engine light and code 41. So I put a new O2 sensor and nothing had changed. Each day the check engine light will come on at the same place going to work. It's probably the exact amount of time the engine is run until I reach this point in the road. It's almost a game to me to see how accurately time wise it takes to come on. I then stop at the local store for a morning drink shutting off the engine. I restart the engine and leave. About the same spot on the highway the check engine lite comes on. On the highway if I rev the engine to 4500-5000 RPMS (after throwing in the clutch) the engine light goes out. About 10 minutes later it come on as I approach work. It is this accurate daily. It does the same thing on the way home from work, just at different locations and duration of time. The check engine light is never on when I start the truck. Usually when I'm approaching work or home after the 25 minute drive the idle is rough, dipping enough to affect the alternator charging which makes headlights surge dim and bright, dim and bright, etc... Also there is a rich odor from the exhaust. I went from 18-19 MPG to 9-10 MPG. I've seen a bunch of hunches and guesses on posts that have similar issues as mine. I don't want to start replacing things randomly. Is there a way to figure out what is going on? I don't plan to take it to a garage or dealer. Thee has to be some intelligent way of figuring this out. So has anyone dealt with this and figure things out? appreciate you taking the time, thanks!

 

[kimcrwbr1]

Did you erase the memory and reset the computer when you changed the O2 senser? If not disconnect the battery for 1/2 an hour to reset the values. Then see how it runs? You must allways erase the memory and reset the computer after you clean or replace a senser then check the codes to confirm the repair.

 

[Fairlaniac]

I erased them via the scanner. However I'll give it a shot and disconnect the battery over night.

Thanks,

 

[enjr44]

The o2 sensor is throwing the code. Not because it is bad, because the fuel trims are out of wack. 41 is a lean code.

From XXX miles away, I think the computer is trying to add fuel because it is being told there is more air going through the engine than there actually is. When it runs out of the ability to keep it at 14 to 1 ratio the o2 sensor lights the light. When the engine is cold it is supposed to run rich. So the computer really doesn't care what the o2 sensor is reporting.

So my GUESS (for what it is worth) is the MAP sensor is putting out the wrong info and the computer keeps trying to add fuel to get it in balance.