no A/F ratio reading anymore???

[neikoblu]

I went on a 1200 mi. trip from La. to Fl. Everything was fine but on the way back the A/F reading started to slowly decrease. It would stay stoic. then it just slowly started to drop down to lean and then it wouldn't even read anymore. It usually would go back and forth but now it doesn't even read anymore. Also, the car started to act up like it was dropping cylinders or something but only once in a while (every 5 min. or so). I fiddled with the MAF sensor plug but that didn't seem to help. I don't know what to do. I check the connections to the A/F ratio gauge and the wiring to the O2 sensors. Could this much miles traveled at one time make the O2 sensors go bad? I don't know what the deal is. I would appreciate any help at all. Thanks

 

[superhuaman]

Are they the original O2 sensors? If so, I would have them checked out and if bad, replaced. Since you're having driveability problems along with your gauge reading, it means that it's not your gauge.

 

[neikoblu]

Is there really a way to check the O2 sensors on a car. I pulled the codes but it didn't pull a code refering to the O2 sensors being bad. I might just replace them but they aren't that cheap.

 

[superhuaman]

Yes, you can use a volt meter, a scope, or an O2 sensor tester.
Jrichker, come in please

 

[dragnazz5.0]

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

this diagram might help y0u figure 0ut what wires need t0 be tested. id just check f0r c0ntinuity. there is really n0 way t0 check t0 see if the 02 is switching with0ut a sc0pe th0ugh. g00d luck

 

[jrichker]

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts