<TABLE width="100%" border=0 itxtvisited="1"><TBODY itxtvisited="1"><TR itxtvisited="1"><TD vAlign=top itxtvisited="1">My 89 bronco II 2.9l, is reaaly causing me a headache, About a 3 weeks ago, my check engine light came on, so I pulled my codes, to find out that it only read 11, 10, 41. Since I know that the 41 was the o2 sensor, I went out & bought a new one. it was fine for 2 days, & then the light came back on, so I re-read the codes to find out that the o2 sensor was at fault again, so I took it back & got a new one. Only to still have my codes show that the 02 sensor is still the fault. To help anybody diagnose my problem the check engine light only comes on when I've been driving for a while, but once the truck it turned off & back on no light. To make a longer story short, could there be something else wrong that's saying its my o2, ie; my egr value, (which I have no idea where to find that), my throttle body being plugged, or any other sendor, Any replies would be great, I want to get my fuel mileage back, last few times, I was only get 5.xx.

Thanks
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41 is system lean, probably not the 02 sensor.

Check the fuel pressure and also check the injector harness "ground" up on the intake, make sure its clean and tight. Passenger side right about in the middle.

If you find any fuel in the fuel pressure regulator's vacuum line, replace the regulator.

 

If it has a Mass Air Sensor, you might want to check that. I have a Mercury that gave me a fit, it was doing the same thing your discribing.

If its getting a incorrect reading from the Mass Airflow Sensor, i will think that your not getting any air through your intake which will lean your fuel out, enough to make it miss.

 

you might take a look at the map sensor

 

AS you have discovered, codes by themselves don't tell you what is wrong. Pulling codes is just the first step in diagnosis.

Next thing I'd do in your place would be to run the KOER test to see if you get a corresponding KOER 41 to go with the CM 41. These things can be easier to diagnose from the KOER test because KOER codes represent "here and now" faults rather than "sometime while driving" faults.

This kind of code means that the computer is seeing a problem in fuel mixture control. Because the computer's primary purpose in life is to control fuel/air mixture, there are a lot of possible causes. "By the book" diagnosis usually starts by checking fuel pressure and checking for vacuum leaks. As noted above, this can include the MAP sensor (your '89 2.9 doesn't use an MAF).

If you pull a few spark plugs, does their condition indicate that the engine is indeed running lean as indicated by the O2 sensor, or is it really running rich?

Don't forget that the computer can't see past the end of its proverbial nose. Any breaks in the wiring between the O2 sensor and the PCM (leaning against an exhaust manifold or pinched between the transmission/engine, for example)?

 

I see that you're truck has a 2.9 litre . The previous post is correct the code is just that a code. How ever a little heads up for you these motors often get vacuum leaks internal from the intake manifold gaskets. A simple test is to un plug the pcv valve from the valve cover and remove the crank case vent from the other valve cover. Now plug both hole with you're fingers , Do you feel vacuum ? If so then I suspect you already know the answer. If no vacuum then like the previous post said there may be several reasons for the pesci code 41. If I can be of any help please do not hesitate to and I can prob walk you through most if not all of the required tests from memory . good luck