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Old 05-23-2011, 10:10 PM   #1
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Join Date: May 2011
Location: Nicholson PA
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89 K2500 Lean (Code 44)

I have an 89 K2500, auto, which was swapped to a 305 (from 350) from a previous owner.

It throws a 'service engine soon' light after ~15 mins of driving, accompanied by a loss of power.

After checking the code, it's throwing code 44 - engine running lean.

The fuel pump, tank, and fuel filter is new. The injector spray pattern seems normal, and there's no residual drips after shutting the motor off.

The timing of the service engine soon light, and the error code lead me to believe the O2 sensor was feeding bad data to the ECU when it went into closed loop.

After a moderately difficult time, I replaced the O2 sensor.

Unfortunately, after taking the truck for a test drive the service engine soon light (code 44) persisted. (after about 20 mins of drive time)

I've looked over the exhaust both to the front and the rear of the o2 sensor, and there does not appear to be any leaks.

What's my next move here? I'm kinda stumped.

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Old 05-23-2011, 11:25 PM   #2
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Location: Huffman,TX
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Re: 89 K2500 Lean (Code 44)

Chevy tech will chime in on this... i'm sure...he has some really good information....

replacing the o2 sensor was a good guess, and a good place to start.

I would want to check fuel pressure and the coolant temp sensor for the ecm.....

fuel pressure is hard to check on the tbi engines. but the coolant temp sensor for the ecm is very easy to check.... check the resistance readings of the sensor and also the connector for the sensor, and the ground wires located on the thermostat housing.

link for checking coolant temp sensor

link for checking fuel pressure

Last edited by tommie; 05-23-2011 at 11:28 PM.
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Old 05-24-2011, 07:58 AM   #3
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Re: 89 K2500 Lean (Code 44)

How do the wires going to the O2 sensor look? Make sure there are no possible shorts there....
Also, check for vacuum leaks.
69 Chevy C10

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Old 05-24-2011, 08:33 AM   #4
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Re: 89 K2500 Lean (Code 44)

The lines near the O2 sensor look great actually. I'll trace them out and check for continuity.

Any particular place to check for leaks? I assume around the TB is a good place to start?

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Old 05-24-2011, 10:12 AM   #5
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Re: 89 K2500 Lean (Code 44)

Anything that causes it to run to lean, or causes the ECM to detect that it is running to lean, will set the code 44.

A dirty fuel filter.

Low fuel pressure.

Melted or damage insulation, allowing the o2 sensor wire to come in contact with metal, grounding the circuit.

Exhaust system leaks ahead of or near the o2 sensor can allow extra air to reach the O2 sensor causing the code.

A.I.R. Air Injection Reaction (smog pump) system valve failure on vehicles with this equipment.

A bad O2 sensor can cause a code 44, but usually a bad o2 sensor will set a code 13.

Voltage must remain below .1 volt, while in closed loop operation, for a specific amount of time (which this time specification varies greatly from system to system)

Does the truck have A.I.R. (a smog pump)?

Drive it until the problem shows up and then unplug the O2 sensor and see if it runs better with the sensor unplugged.

This will help reveal if it is really to lean or if the ECM thinks it is to lean and is making it go to rich.
For those of you that are wondering why you are not getting replies to your thread:
Did you give the model, year, engine, fuel system type, and transmission information?
If it is modified from what came stock from the factory, let us know that too.
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