Oxygen Sensor

My 98 Escort oxygen sensor went bad at the wrong end of a 1000 mile road trip. I noticed NO changes in driving performance other than a slight decrease in gas mileage.

I expected the engine would run a bit "richer" (explains lower mileage) and the emissions would increase until I could replace the sensor and reset the error code. Mileage did increase slightly (back to normal) after the repair.

OK,

I was hoping that it would have. The Car has developed a funny Knock. Where it knocks like it sounds like a Big Diesel truck engine. But it does it at a very odd time I have never ever had a car do this before in my life and I've been driving since 1970.

At a very narrow I guess torque window is when it knocks, and knocks BADLY! You can hear it echo off buildings nearby,. Here is when it does it.

Imagine you in a city, and moderate traffic youre at a stop intersection and it's youre time to go. You press the accelerator just a tiny amount above idle to move along in traffic, Like 1/8th throttle or so, This is when it knocks.

Any more nothing or any less nothing. But it makes it hard to drive in town. Because to keep it from Knocking ya gotta have like 1/4 throttle or more, Or idle. That 1/8th position like city driving is when It knocks. Even BIG hills etc. nothing just that small window slightly above idle.

What may be wrong with the engine.?

What's wrong with the engine is that the exhaust oxygen sensor is faulty, as noted by the diagnostic. The engine control unit has modified the timing so that at some speeds pre-ignition ("knocking") is occurring. As it has reached the end of its adjustment algorithm, the diagnosic is occurring.

The fix is to replace the faulty sensor.

Your oxygen sensor just basically gives you better gas mileage by metering the gas flow by oxygen in the exhaust fumes. The sensor does not actually measure oxygen concentration, but rather the amount of oxygen needed to completely oxidize any remaining combustibles in the exhaust gas. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess. Also it helps with better emissions as well.

Just because you have a code doesn't mean the sensor is bad. A cracked exhaust manifold,leaking intake gasket or broken vacuum hose will set of a code.

Stalling at start up, poor idle or other problems will occur.

A cracked exhaust manifold doesn't need a computer diagnostic. It will be audible to the Mk.1 eardrove. ><

I concur with sjw40364... a bad oxygen (O2) sensor won't cause issues you'll notice while driving.

The O2 sensor controls fuel mixture/emmisions which most likely won't cause a knock, smoke or any outwardly noticeable signs if it goes bad. If you live in an area that requires emission testing, a bad O2 sensor could cause you fail the testing.

Had one fail in a '91 Shadow and it went lean like it was running out of gas on hills. I was told they usually go rich but mine went the other way. Changed O2 sensor and it corrected the problem. $45 for the sensor and $22 for the socket to change it.

Engine runs rough. Stalling.