Codes 172, 173, 176, 177

[mg655321]

I've got a 94 4.0 V6 and I've been getting these codes. They say that the engine is running both rich and lean on both the left and right sides, according to the oxygen sensor.

The truck runs like crap, horrible hesitation, won't run in overdrive, until I manage to get it up to about 80 MPH at which point it runs like a raped ape.

I'm guessing the O2 sensor is just bad. Do you know of anything else that can cause all of those error codes at once? Thanks.

 

[dogfriend]

Other than the O2 sensor, make sure that the wiring to the O2 sensor is ok.

All of your codes relate to not getting the expected signal back from the O2 sensor, so it seems to be a good bet that its bad.

Does it run reasonably ok when cold, then run like poop when warm? That would show a problem with the feedback (O2 signal) when running in closed loop (warm).

If it also runs crappy when cold and / or idles rough, then you could have a vacuum leak or other problem which is throwing the fuel/air mixture off. This might also give you similar codes.

 

[mg655321]

It actually runs worse when cold. So perhaps it could be an intermittent vacuum leak too, that throws the mixture from lean to rich as the leak opens and closes. I checked the fuel pressure today, that was fine, guess its time to invest in a vacuum gauge as well. Does the O2S need periodic replacement as a rule? If so I can replace it, just to rule it out.

 

[Jason_25]

You have two 02's, one on each side. I'm definitely thinking vacuum leak.

 

[dogfriend]

Yes, if yours is running crappy at idle and while cold, then you also have something else wrong and a vacuum leak is a likely suspect. A vacuum leak or a leak in the air intake system downstream of the MAF will let in "false air" and screw up the fuel/air mixture.

O2 sensors do eventually go bad, I think because they get coated with stuff from the exhaust system which slows down the response or "switching time". It is possible to test for this with a scan tool; you would watch how many times it switches during a time period and compare to spec.