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o2 sensor


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The O2 sensor indicated the oxygen level in the exhaust gasses. This info is used by the ECU to make adjustments to the fuel injection or the feedback carb's fuel mixture to keep it at the optimal 14.7 to 1. Without it the ECU has a fallback setting of over rich and mileage will drop.

 

Does your 'carb' have one or two wing nuts holding the air filter on? One would be the feedback carb. Two would be throttle body fuel injection.

 

The two wire 'thing' at the base of the carb is an electric heater to warm the intake air on initial cold start up. It helps evaporate the gas and lowers hydrocarbon emissions..

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OK you have the feedback carburetor. The throttle body EFI engine also has the O2 sensor so just checking.

 

Once warmed up and not at full throttle the O2 sensor tailors the air fuel ratio to achieve an ideal 14 or as high as 15 to one. This results in the most ideal combustion and least amount of hydrocarbon emissions.

 

A failure of the O2 sensor causes the system  to default into a 'limp home' mode of extra rich to prevent engine damage from an accidental over lean condition. Over rich will produce huge quantities of hydrocarbons or CO (carbon monoxide) that the cat cannot handle.

 

Not much info on testing.... Find the control unite under the driver's seat. It has a flashing inspection lamp on it. Warm engine thoroughly. Rev to 2 K and hold there under no load for two minutes. Inspection lamp should flash more than 4 times in 10 seconds.

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Oh well if this is the reason for the 02 question, it could be anything. 

 

Running rich or high CO level, possible causes...

 

Choke not shutting off

Water temp seder not working, ECU thinks engine is still warming up

O2 sensor disconnected, broken...

Plugs mis firing... wires,cap rotor?

Carb float level too high... flooding

Air filter dirty

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  • 2 weeks later...

So, for the Cali feedback carbureted trucks, there's a red LED on the ECU, which is mounted beneath the driver seat.  The LED is on when the O2 sensor is reading rich, and off when it's reading lean (or the other way around; I can't remember).  If your truck is running properly, you should see that light switch on, off, on, off, on, off...

 

The water temperature sender doesn't do anything other than to drive the temp gauge.  If you suspect that the engine isn't coming up to temperature, get an infrared (non-contact) thermometer, and check.  Proper running temperature is 80 degC.  So if you get water circulating through the radiator when the engine is below 80 degC, you likely have a bad thermostat (stuck open or something like that).

 

Do you have the actual numbers from the smog test / gas analysis?  Those would be useful in helping figure out exactly what's going on.

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How do you know if the water temp sender is failing

 

The gauge sender is just under the thermostat housing on the front of the intake. Unplugged it will read full cold. Ground the sender wire and it will read full hot on the gauge. Poor or loose connection is the usual cause of a intermittent reading.

 

 

 

 

 

So today I took the truck in for a retest and everything passed except that Im now running lean and have high NOx. The smog guy said it could be the egr valve or the timing.should I try to clean the egr or buy a new one?

First check that both the intake and the exhaust side plugs are firing. Dual plug operation is essential to lower NOx levels.

 

Now check the timing. Three degrees +/-2 degrees BTDC

 

Not necessary to replace EGR valve but they do need periodic cleaning. Unbolt carefully and clean the underside with a wire brush. Check that it is sealed when closed and no carbon holding it open. A leaky EGR will usually have a poor idle. Also check the metal pipe back to the exhaust manifold. Any holes will let in oxygen and this will lean out the mixture when driving.

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