1997 ford ranger 2.3

[preemanc]

Yes i was wondering if someone can help me out a little . I have a 97 ranger with a 2.3 , i keep getting a P0171 code ( system too lean bank 1 ) i have changed fuel filter , air filter and also cleaned MAF sensor , i changed the plugs and wires , also changed the intake gaskets and in the process took the time to go through the vacume lines and all are fine - i still am getting the trouble code P0171 and im dumb founded and cant seem to think of what else to do . I asked a mechanic and he said its throwing a lean code there for my o2 sensor is registering and working any suggestions ?

 

[tomw]

The O2 sensor is finding Oxygen molecules floating by in the exhaust stream. It does not expect there to be any extra if the fuel air mix ratio is correct. They should all be consumed in the combustion chamber when the spark plug ignites the mix. Because they are there, the O2 tells the ECM that it needs to send more fuel for the amount of air coming in, in other words, enrich the mix with more gas. It can only go so far, and is limited in how much more gas can be flowed. There are two measures, short term and long term fuel trim, which can be read in OBD-II systems. Ok, that's the logical part, now you need to know the practical. If there is extra air at the O2 sensor, it can be caused by a misfiring ignition system leaving un-burned fuel and extra O2, by leaks in the exhaust system allowing air to pass by the O2, by leaks into the intake manifold adding air the ECM doesn't know about.
You could also have a lack of fuel caused by low pressure, low flow, or injectors that don't flow enough fuel. I think I would check the fuel pressure, the pressure regulator and the amount it flows. Some Rangers had two fuel pumps, a lift [pickup] pump in the tank and a pressure pump on the frame rail under the drivers seat.
tom

 

[gjm4l]

^hes right. Butttt i was getting the exact same code on my 92' 2.3 I checked and replaced exactly what you did and was having start up issues as well. I just replaced my O2 sensor and bam problem solved she runs like a top. Not saying thats what it is for you because i expected everything the above poster suggested but if the O2 goes bad it can cause some interesting stuff without ever being out of the ecu's "range of operation" to throw a sensor code. Besides it being a last resort (a how could it be but what if it is type thing) plus realizing it was the oe part on a 160k engine i went for it and that was my golden ticket. Good luck

 

[tomw]

Hmm, I thought that OBD-II would tell the brainz that the O2 was not doing anything, so to speak. I had it in my mind that there was a 'checker' O2 sensor after the catalytic that tattled on a poisoned cat, but, I thought, would have compared readings with the upstream O2.. and reported that one or itself as 'one of us is nutz' so to speak. But what do I know.
To reinforce how the O2's work, I used the mnemonic: Low == Lean. Implying to myself that the low voltage reading from an O2 indicated a lean condition.
I suspect that if an O2 fails, it will cease producing voltage, and thus throw a 'lean' code. That would explain the code shown.
tom

 

[gjm4l]

Yep thats how it works, you explain the operation better than me too lol. But the sensor isn't on/off, theres alot of middle ground for sorta works since its reading air/fuel it can get clogged to where its in max/min spec(ala no code) but it isnt reading properly causing problems. Yep its rare the first one i saw was my 92' which had the op's code but was running rich. Do 97's have 2 O2's? I cant remember if OBDII'S added the second or if it came in with the new style engine. Cause yep that would make it even stranger and less likely since they'd be on the buddy system as mentioned but still not impossible. Another thing to look for is cracked, burned, exposed or otherwise damaged wires. Oh and tomw, you probably know ALOT more than me I'm just saying it's not cut and dried is all