Trouble Codes

[noclrnce]

I have an 87 R30 with the 7.4. The previous owner installed headers. I had the pipe drilled and had an exhaust bung installed along with a new Delco sensor. The other day I had two codes show up. I can't remember the numbers but I ended up replacing the egr valve and the map sensor. Now the check engine light will come on for a bit then turn off for a bit at random. It never stays on constantly. I checked the codes and it is code 44 which is oxygen sensor circuit - lean exhaust detected. Where should I start? Should I replace the O2 sensor or could my issue be somewhere else?


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[Captain Swampy]

Check ground wires. Battery to fender, by thermostat, right rear of block to cab, and any others you can find.

[noclrnce]

Grounds all look good and are tight


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[bd]

Does the engine misfire?  Look/listen closely for any exhaust leaks (even minor leaks), especially upstream of the O₂ sensor to within about two feet downstream.  Inspect the O₂ sensor lead to make sure it isn't chafed or melted to ground.  Verify that the O₂ sensor is properly grounded through the exhaust pipe connection to the engine - the pipe is solidly and electrically connected to the engine.  Remove and blow through the inline fuel filter to check for restrictions then measure the fuel pressure with a gauge.  Check/spray for vacuum leaks.  Check the air management system to make sure it isn't pumping air into the exhaust during closed loop.  Try to determine whether there is any pattern to CEL illumination rather than being random (e.g., generally occurs at highway cruise, etc).  You get the idea?  If everything checks/tests okay, replace the O₂ sensor.

Reference:  1987 Light Duty Fuel, Drivability and Emissions Manual

[noclrnce]

Thanks for all the replies. I'll get to work.


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[noclrnce]

No misfire by the way. The light has been coming on after warming up. On the way home from work tonite I got on the highway. It took a minute to come on then it would go off for a few minutes then come back on.


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[Irish_Alley]

does it do it while your just cruising. then once you get back on it after a while it will shut off?

[XrayTedd]

If the headers are long tube headers you may need to switch to a 3 wire heated O2 sensor. Ones the sensor gets 12" or more off the heads, it is harder for them to get hot enough for accurate readings.

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[noclrnce]

While sitting in line at drive thru the light was not on. As soon as I pulled away and got on the road the light came on. I noticed today while in park it has a slight stumble.


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[bd]

...Look/listen closely for any exhaust leaks (even minor leaks), especially upstream of the O₂ sensor to within about two feet downstream.  Inspect the O₂ sensor lead to make sure it isn't chafed or melted to ground.  Verify that the O₂ sensor is properly grounded through the exhaust pipe connection to the engine - the pipe is solidly and electrically connected to the engine.  Remove and blow through the inline fuel filter to check for restrictions then measure the fuel pressure with a gauge.  Check/spray for vacuum leaks.  Check the air management system to make sure it isn't pumping air into the exhaust during closed loop....

Reference:  1987 Light Duty Fuel, Drivability and Emissions Manual

In addition to the above, check the TPS function using a digital voltmeter.

[noclrnce]

How do I check the tps voltage? What should it be at?


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[Irish_Alley]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0

[bd]

Using a digital voltmeter set to the 10 VDC scale, with the factory wiring harness connected to the TPS, measure between the gray and black wires.  Switch the ignition ON.  The voltmeter should indicate 5 VDC.  Now, connect the voltmeter between the blue and black wires.  With the ignition ON, engine not running, slowly rotate the throttle from idle to full throttle.  The voltmeter should measure a smooth increase in voltage from ~0.5 VDC at idle to ~4.8 VDC at full throttle.  Next, slowly rotate the throttle closed to idle.  The voltmeter should indicate a smooth decrease in voltage to the initial 0.5 VDC reading.  Cycling the throttle multiple times should yield identically repeatable results. 

The initial 5-volt reading indicates the proper reference voltage supplied by the ECM.  The gradual transition from 0.5 volt to 5 volts and back as the throttle is opened and closed indicates the function and quality of the sensor.  If the voltage change as the throttle is opened and closed is erratic, the sensor should be replaced.

Have you performed any of the other checks previously mentioned?

[noclrnce]

I have not. Can only work on this on weekends. It's dark usually when I get home.


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