2008 Grand Prix 3800 SE3
I drove the car more than usual last December while I was going uphill on a highway when a sudden loss of power occurred that was temporary, no codes.
I went straight to an expert who test drove it violently and did not notice a difference but he "felt"a lean condition even though he couldn't see real evidence in the live data.
A few days later the light and code came on.
I don't sense any symptoms but may be a barely noticeable loss of power, but if I reset the code the light comes back on in no time (a few miles of driving).
I studied this video P0171 Trouble Code: System Too Lean Bank 1 Diagnosis - YouTube (great guy and great video) and I have a cheapo scanner and a Haynes book for this car (and off course the internet) I started investigating
and this is what I did so far:
1. checked all the vacuum ducts and hoses that I know of (couldn't find a vacuum diagram online for an 08 that I could understand or a sticker under the hood)
2. I replaced the PCV valve and the air filter just because I haven't replace those for over a year (probably have nothing to do with the issue)
3. I have an intermittent (almost rare) PO446 that comes once a year or so but I never investigated thinking that it's probably just a gas tank not closed well after a fill or just getting old.
4. I tested the MAF by recording the g/s at equally spaced rpm readings and it was a straight line relationship with normal values (1-15 g/sec). So the sensor is fine but I cleaned it anyway with the appropriate spray anyway not long ago.
5. I drove around a little and started watching the trims and O2 sensor readings after warm up and closed loop an the O2 sensors where going up and down (0.1-.9) as they should (eliminating sensors and their wiring). The fuel trims where both crazy high (teens-30's) as soon as I remove my foot from the gas pedal but go to close to zero as soon as I tough the pedal. That is almost always a vac leak indication, right?
6. I pulled the freeze frame:
Freeze frame information:
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Fuel Status = 0 byte
Engine Load = 20.392 %
Engine Coolant Temperature = 86 °F
Fuel Trim Bank 1 Short Term = 10.938 %
Fuel Trim Bank 1 Long Term = 16.406 %
Intake Manifold Pressure = 4.931 psi
Engine RPM = 1,012.5 rpm
Speed (OBD) = 0 mph
Timing Advance = 11.5 °
Intake Air Temperature = 30.2 °F
Mass Air Flow Rate = 6.37 g/s
Throttle Position(Manifold) = 6.275 %
Air Status = 0 byte
Run time since engine start = 182 s
EGR Commanded = 0 %
EGR Error = 0 %
Fuel Level (From Engine ECU) = 40.392 %
Distance travelled since codes cleared = 20.505 miles
Evap System Vapour Pressure = 14.5 Pa
Barometric pressure (from vehicle) = 14.359 psi
Catalyst Temperature (Bank 1,Sensor 1) = 572 °F
Voltage (Control Module) = 14.265 V
Engine Load(Absolute) = 16.471 %
Commanded Equivalence Ratio(lambda) = 0.977
Relative Throttle Position = 0 %
Ambient air temp = 28.4 °F
Absolute Throttle Position B = 6.275 %
Accelerator PedalPosition D = 0 %
Accelerator PedalPosition E = 0.392 %
End of report.
I have a first timer question about searching for vacuum leaks. Do propane test and smoke machine test do the same thing? what is the difference if so?
This is probably going to be my next task as soon as the endless rain/snow ends outside, and looking forward to some wisdom and guidance from the experts here.
Vinny
