Hello

I have a 1999 Ford Ranger with the 4.0 and the automatic transmission. I have an on/off again (mostly on) CEL that reads P1131. The truck runs fine, although it does run rough while in gear and idling from time to time. This is faily rare, but when it does do it the engine is never fully up to operating temp.

I have recently replaced the upper intake gaskets (the rubber figure 8 things) and the fuel rail gasket which fixed code P0171 I was getting. But P1131 just won't go away! EEK!

My truck has 125K on it. Within the last 25K I have replaced the plugs with Motorcraft plugs, the fuel filter, the air filter, the IAC Valve, and the intake and fuel rail gaskets I mentioned earlier.

Can anyone give me some insight on where I should be looking? I don't know where to start. All the definition of my trouble code says is "Lack of Bank 1 O2 transitions- Lean. ECM detected bank 1 O2 is at its lean limit."


Thank You
Chris

 

It could be that the 02 sensor is bad (passenger side, on the exhaust manifold).

 

Is there any way to test the sensor? I have a DMM.
They are kind of expensive to just "try" if you know what I mean.

 

p1131 says the o2 senor is not switching It is probably bad.