codes 173 and 177

[alwaysFlOoReD]

Oxygen sensor not switching – system is or was rich

173 is left bank
177 is right bank.
What causes an O2 sensor to not switch? Is this a sign of leaking injectors?

My trucks' cel comes on intermittently, and fuel mileage has dropped drastically. Recently replaced both o2 sensors, new y-pipe and the ect sensor with a good used one. These got rid of some other codes.

Update; I tried to start the truck with my foot to the floor on the gas. It didn't start or show any signs of trying to start. I guess that rules out leaking injectors.

Thanks,
Richard

 

[RonD]

Leaking FPR(fuel pressure regulator), check its vacuum line for gasoline, cranking vacuum(2") may not be enough to suck in the fuel in FPR vacuum line but running vacuum(18") could

Plugged exhaust can cause it as well but you should notice a loss of power above a certain RPM with that
Test for this with a vacuum gauge

 

[Uncle Gump]

What causes an O2 sensor to not switch?

An O2 sensor has to be hot to work... then it compares ambient oxygen to oxygen in the exhaust stream and generates a small amount of voltage based on the differential. So an O2 sensor is really a little battery that will generate between 0 and 1 volt but only after it is hot. That's why they put a heating element internal to the O2 sensor. It makes the sensor come online sooner and keeps it online. The higher the voltage... the richer the exhaust (lack of oxygen) and vice versa.

I would check the power and ground circuits of the O2 sensors.

 

[alwaysFlOoReD]

I checked vacuum, running at 21, so no problems. I then switched the fpr and the problem cleared up.
A code 522 came up but that is for the nss (clutch sensor). Ill worry about that another day. Thanks for the help everyone.