1996LT1Z28

Bought an Autel AL519 OBD2 scan tool.

It records live data and stores it for future use, which is nice.

Ran a scan, and noticed that the timing is always set at -24 deg advance.

-24 deg advance?????

The car burns gas like there is no tomorrow...there is something definitely wrong with the ECM....you can see the data change, but the O2's look like they are dead...I have a new set of O2's. Gotta change them.

If I get a chance, I'll post the entire set of data points.

Hopefully, someone can give me some pointers if possible.

shoebox

Timing should vary upon operating conditions, not stay the same all the time. There is nothing wrong with 24%u00B0 advance if it is applied at the correct time. Don't get caught up with the negative sign with the number. It's always going to be negative. Negative just means advance (though negative advance is really a double negative). Some scan tools just don't know how to say it right.

If your O2s are dead, you mileage will surely suffer.

Injuneer

Any codes? "static" O2 sensor readings should set codes.

1996LT1Z28

Here's some of the Live Data points. I took 30 readings. The two here are the first & last data points:

Over the entire 30 scans, the O2 readings are over the place. These are the old O2's. I'm planning on replacing them.

Do these look normal?

Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 statusCL
Calculated LOAD Value(%)2.7
Engine Coolant Temperature(¡£C)91
Short Term Fuel Trim -Bank 1(%)-2.3
Long Term Fuel Trim - Bank 1(%)-7.0
Short Term Fuel Trim -Bank 2(%)-3.1
Long Term Fuel Trim - Bank 2(%)-0.8
Intake Manifold Absolute Pressure(kPa)36.0
Engine RPM(rpm) 654
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)-15.0
Intake Air Temperature(¡£C)28
Air Flow Rate from Mass Air Flow(g/s)6.88
Absolute Throttle Position(%)0.0
Commanded Secondary Air StatusOFF
Location of Oxygen SensorsB1S12--B2S12--
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.150
Short Term Fuel Trim Bank 1-Sensor 1(%)-1.6
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.150
Short Term Fuel Trim Bank 1-Sensor 2(%)N/A
Oxygen Sensor Output Voltage Bank 2-Sensor 1(V)0.745
Short Term Fuel Trim Bank 2-Sensor 1(%)-3.1
Oxygen Sensor Output Voltage Bank 2-Sensor 2(V)0.660
Short Term Fuel Trim Bank 2-Sensor 2(%)99.2
OBD requirements to which vehicle is designedOBDII
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Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 statusCL
Calculated LOAD Value(%)2.4
Engine Coolant Temperature(¡£C)92
Short Term Fuel Trim -Bank 1(%)-3.1
Long Term Fuel Trim - Bank 1(%)-7.0
Short Term Fuel Trim -Bank 2(%)-2.3
Long Term Fuel Trim - Bank 2(%)-1.6
Intake Manifold Absolute Pressure(kPa)36.0
Engine RPM(rpm) 669
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)-16.0
Intake Air Temperature(¡£C)28
Air Flow Rate from Mass Air Flow(g/s)6.78
Absolute Throttle Position(%)0.0
Commanded Secondary Air StatusOFF
Location of Oxygen SensorsB1S12--B2S12--
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.830
Short Term Fuel Trim Bank 1-Sensor 1(%)-1.6
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.150
Short Term Fuel Trim Bank 1-Sensor 2(%)N/A
Oxygen Sensor Output Voltage Bank 2-Sensor 1(V)0.575
Short Term Fuel Trim Bank 2-Sensor 1(%)-2.3
Oxygen Sensor Output Voltage Bank 2-Sensor 2(V)0.690
Short Term Fuel Trim Bank 2-Sensor 2(%)99.2
OBD requirements to which vehicle is designedOBDII

moparman

O2 sensor readings should be going all over the place. Should be changing fairly rapidly. It's when they're stuck on one reading that there's a problem.

1996LT1Z28

Thanks for the quick reply moparman....

Do the readings look normal???? Don't know much about these things.

Injuneer

I looked over the 30 frames of data you sent me. There isn't a lot to be learned from frames of data without time stamps on them. I tried manually typing the data into Excel, but it was too time consuming.... gave up after about a half-dozen frames.

The conclusions I was able to reach by simply looking through the data:

-You were sitting at idle, and the fuel trim data is for Cell 16. Doesn't tell us anything about the other 17 cells.

-The engine coolant temp shows 91*C = 196*F. Was your engine fully warmed up? Appears normal.

-Long Term Fuel Trims (LTFT) show Bank 1 (driver's side) is subtracting 7% of the normal fuel calculation to keep that bank from running rich. Bank 2 (passenger side) is subtracting less than 1%.

-STFT's toggle back and forth with the O2 sensor readings.... normal.

-Manifold absolute pressure is 36kPa. That would be normal at idle, throttle closed, stock cam.

-Engine RPM stays around 650RPM, with normal fluctuations. This would indicate your car has an A4 transmission, and it was in "park". You need to add a "signature" with basic info about your car - year, model, engine, trans and any major mods.. I know you have some of the info in your screen name, but there are people here who don't have the same vehicle as their screen name would indicate. The target idle speed, engine fully warmed up, for an A4 in park/neutral is 650RPM,

-Vehicle speed is "0".... since its parked

-Ignition advance varies from 13* - 17* before TDC (hence the "-" sign as noted in posts above). Seems normal. I'm used to the M6's higher idle speed (800rpm) where stock timing is more like 20*, but yours seems OK.

-Intake air temp = 28*C = 82*F. Typically this will be a few degrees above ambient temp, due to heat soak of the inlet air ducting and the IAT sensor.

-Mass air flow is high 6's.... e.g. 6.88 grams/sec, which is normal

-Throttle position percent = "0" since the throttle is closed.

-AIR pump status is OFF, since the PCM has entered closed loop = normal

-The "Position 1" (pre-cat) O2 sensors appear to be cycling back and forth from rich to lean normally. This is where you can't really tell what is happening without a time stamp, but they look OK.

-After cat O2 sensors appear to be dampened from the pre-cat readings, which is normal. But it seems odd that Bank 1 is mostly on the low side, and Bank 2 is mostly on the high side. Again, without the time stamp, hard to evaluate.

-There is a strange reading for "Short Term Fuel Trim Bank 2-Sensor 2 (after-cat sensor) of +99.2%, which makes no sens at all. That may be a glitsch in the scanning software.

Have you inspected the spark plugs? Do they all show they are running rich, producing the poor fuel mileage, or is the problem limited to one bank or specific cylinders? I'm going to assume the car has cats, and you aren't running O2 sims in the after-cat position.

Is there any way you can run a full scan, all the parameters, for an extended period of time, and produce the data log in .csv, Excel, or .uni format? It isn't unusual to receive data logs with up to 10,000 frames of data, with 8 frames per second.