O2 sensor works for a while then goes rich?

[FONT=&quot]Question? I have a situation where one of the O2 sensors works for a while then gives a rich indication. It seems to work just after the engine is warmed up and as the car comes up to operating temperature the sensor gives a rich indication. I have not checked the sensor output while driving as I am currently getting my front seats redone. Has anyone come across this same situation? [/FONT]
[FONT=&quot]For background info cylinder 6 has only 60PSI compression because of some broken rings and this is on the manifold where the sensor seems to be malfunctioning. [/FONT]
[FONT=&quot]The pic shows a fancy milivolt LED dot indicator that I made up to fill the extra space I had when I mounted the boost controller in the lower din section below the radio. The center led lights up when the sensor output is 0.5Volts. Extreme left 0V (Lean) and right is 1V (Rich). This tells me if the sensor and the ECU are functioning as designed. The leds cycle about the middle until the engine warms up to normal operating temp then one goes rich.[/FONT]

 

Could test the O2 sensor with something like a Snap-on MTOST Analyzer, or watch the waveform on a Scope.
Perhaps data log it using ConZult.
In all probability, the issues with No.6 cylinder will be having an effect on the behaviour of the O2 sensor.

 

That is what i was thinking.

I just wanted to see if anyone else had a similar problem.

MichaelZ

 

Sensor may be working correctly and showing you have a rich mixture on that side ?

 

You may be right.

I suspect you are right. I will get one of my seats back while i wait for the other seat to get fixed and i will drive it and check it out.

MichaelZ

 

Drove car. Still one bank rich

Drove the car at 100Kmh for about 30min. Still showing rich on one sensor. I suspect the low compression on No5 is causing the ECU to enrich the fuel.

Thanks for all the suggestions.

 

If one of your your coils isn't firing it's plug, you are going to be rich on that side

 

Never thought of that.

.

Good point. I will check that out ASAP.

 

O2 sensor now working

Drove 600Km at 110 kph and now the sensor and ECU functioning as designed. Fuel consumption has improved markedly.
I'm glad i do not have to replace the sensors. Was not looking forward to that.

MichaelZ.

 

I was chasing o2 sensor waveforms on the net & came across this article on the Pico website:

A lambda sensor?s normal life span is 30,000 to 50,000 miles, but the sensor may fail prematurely if it becomes clogged with carbon, or is contaminated by lead from leaded petrol or silicone from an antifreeze leak or from silicone sealer.

As the sensor ages, it becomes sluggish. Eventually it produces an unchanging signal or no signal at all. When this happens, the Check Engine Light may come on, and the engine may experience drivability problems caused by an overly rich fuel condition. Poor fuel economy, elevated CO and HC emissions, poor idle, and/or hesitation during acceleration are typical complaints.

If the average voltage from the lambda sensor is running high (more than 0.50V), it indicates a rich condition, possibly due to a bad MAP, MAF or Air Flow sensor or leaky injector. If the average voltage reading is running low (less than 0.45V), the mixture is running lean possibly due to a vacuum leak or because the sensor itself is bad.

If the lambda sensor continually reads high (rich), it will cause the engine computer to lean out the fuel mixture in an attempt to compensate for the rich reading. This can cause lean misfire, hesitation, stumbling, poor idle and high hydrocarbon emissions (from misfiring).

If the lambda sensor continually reads low (lean), it will cause the engine computer to enrich the fuel mixture. Injector pulse width will increase causing fuel consumption and carbon monoxide emissions to go up. Constant rich fuel mixture can also cause the catalytic converter to overheat and it may be damaged.

If the lambda sensor?s output is sluggish and does not change (low cross counts & long transition times), the engine computer will not be able to maintain a properly balanced fuel mixture. The engine may run too rich or too lean, depending on the operating conditions. This, in turn, may cause drivability problems such as misfiring, surging, poor idle, and high emissions.

If a heated sensor has a faulty heating circuit or element, the sensor can cool off at idle causing the system to go into open loop. This usually results in a fixed, rich fuel mixture that will increase emissions.

Sometimes an apparent lambda sensor problem is not really a faulty sensor. An air leak in the intake or exhaust manifold or even a fouled spark plug, for example, will cause the lambda sensor to give a false lean indication. The sensor reacts only to the presence or absence of oxygen in the exhaust. It has no way of knowing where the extra oxygen came from. So keep that in mind when diagnosing oxygen sensor problems.

The lambda sensor is also grounded through the exhaust manifold. If rust and corrosion of the manifold gaskets and bolts is creating resistance, it may affect the sensor's output. To rule out a bad ground, use a digital volt meter to check for a voltage drop between the sensor shell and the engine block. More than 0.1v can cause a problem.

 

Read the articale also.

I thought I would try the long drive and it seems to have fixed the problem. The little circuit i built reads the sensor voltage from 0V (left orange LED) to 1V (rightmost Red LED). The led dot indicator goes from lean to rich while cruising. This indicate a sensor reading approximately 0.4V - 0.8V which is about right.

MichaelZ.