P0171 code issues
 

Have a p0171 lean code. Need some help figuring it out. Ass soon as cobalt starts engine stumbles a little. Short trim goes to +30 and long trim goes to +28 . Press on gas and no change until I let off the gas and short trim goes down a little bit and then back up . Here are some freeze frame data in pics. Has new map. New cat. New etc sensor. New air filter. New upper 02 sensor. I've tried 5 different mass airflow sensors. I've smoked tested motor and exhaust with no leaks. I've tried carb cleaner trick while running to see if idle will change no effect. Only thing I notice is fuel pressure key on is 55psi and once I start goes up to 68 psi running 50 to 60 is range but would that really cause a lean code? Also tried a set of different injectors with no change. Ecu is refurbished new also. Any help would be appreciated
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You're throwing a lean code because you're running lean; Fuel Trims maxed out and O2 sensor shows lean. You may as well slap a fuel filter in there, $12...

Do you have hptuners? Need to check your tune or re-flash it with a factory tool. Refurbished ECU might have the wrong fueling (airflow) calibration for your engine because it seems like you've covered most of the bases for this type of problem.

I forgot to add new fuel pump and a new filter just installed also. So ur saying like use a tech 2 to load fuel tables.?

I would try swapping out the down stream o2 sensor.

I've thought about that but everything I've seen that only really tells you the catalytic converter is working. Would it cause a engine misfire or anything?

Mine stuck lean, it was a "post trim" lean code. Can't remember if it was exactly that. The computer uses both 02 sensors, yes the downstream tells the computer if the cat is working as well but the ecu watches both sensors.

This is from my 2006 LE5 engine, so take with a grain of salt:

CIRCUIT/SYSTEM TESTING FOR DTC P0171

• Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The value should be less than approximately 20 percent with the engine running at operating temperature.
• If the value is not less than 20 percent , inspect for the following:
• With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude vs Barometric Pressure.
• If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106. See: P0106
• Vacuum hoses for splits, kinks, and proper connections
• Low fuel pressure
• Fuel contamination
• Properly functioning fuel injectors
• Missing, loose, or leaking exhaust components from the HO2S forward
• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
• The air induction system and the air intake ducts for leaks or for a missing air filter element
• Evaporative canister purge lines plugged or obstructed
• The crankcase ventilation system for leaks
• The HO2S for proper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit
• Malfunctioning engine components

Your baro is off by 1 psi for Omaha Nebraska checked as of now, but I assume you took the snap shots at a different time. Still, if Sensor 1 is reading lean, then by golly the ECU will throw fuel at it, you can see this in the fuel trims. You may have to get down and dirty, continuity check the O2 wiring between the connector and the ECU, and check all those wires for a short to ground. You'd be surprised...

REPAIR INSTRUCTIONS

• Air Cleaner Assembly Replacement
• Air Cleaner Element Replacement
• Air Cleaner Outlet Resonator Replacement
• Evaporative Emission (EVAP) Canister Replacement
• Evaporative Emission (EVAP) Canister Purge Solenoid Valve Replacement
• Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement
• Evaporative Emission (EVAP) Hoses/Pipes Replacement - Canister/Fuel Tank
• Evaporative Emission (EVAP) Hoses/Pipes Replacement - Chassis
• Evaporative Emission (EVAP) Hoses/Pipes Replacement - Chassis/Canister
• Fuel Hose/Pipes Replacement - Chassis
• Fuel Injector Replacement
• Fuel Pump Fuel Feed Hose Replacement
• Fuel Pump Module Replacement
• Fuel System Cleaning
• Fuel Tank Draining Procedure
• Fuel Tank Filler Evaporative Emission Pipe Replacement
• Heated Oxygen Sensor Replacement - Position 1
• Manifold Absolute Pressure (MAP) Sensor Replacement
• Throttle Body Assembly Replacement

Doesn't mention post-cat O2. I'd be interested to find out the logic behind the post-cat O2 causing a major lean running condition. My understanding of the fueling strategy is that if the O2 is reading lean, it will enrich the A/F mixture to compensate.

I only suggest this because it is a refurb ECU. But wait, what is the back story on this car, what happened? The reflash may not work if you swapped the ECU because of this, where the same lean condition was occuring with the old ECU.

It would be nice if you can read the MAF frequency at idle, then compare that with someone else's same vehicle to see if you're way the heck off.

I bought a new ecu because my old one was tuned for my old motor with a supercharger on it. Ar never had a lean issue with old ecu. I could not find the factory tune to reload it on original for original motor.

I've went thru all the steps on alldata to narrow it down but nothing seems to work and or jump out a suggest what's wrong. The other day i found a bad wire from cooling fan to ecu and repaird .and car ran fine a little rich on the short trim fuel but was pretty close to fine.then the next day all of a sudden it threw a p0300 misfire all cylinders and a p0171 but misfires went away and left me with the lean code.

Map sensor was withing spec 96kph I believe key on engine off