MAF question on LTFT tuning

[JLowe5700]

I have a stock 2004 GTO with the only modification is LT Headers. I checked the fuel trims after the header install and was getting very high numbers. I did a test drive without the MAF and the numbers are decent. Attached is my tune, and a log with and without the MAF. Note I did reset the LTFT before each log file. The can runs great and pulls really good, have not seen any Knock either. Hate to mess with it too much, but would like to get the fuel trims back in line. Any suggestions?

[mowton]

I have a stock 2004 GTO with the only modification is LT Headers. I checked the fuel trims after the header install and was getting very high numbers. I did a test drive without the MAF and the numbers are decent. Attached is my tune, and a log with and without the MAF. Note I did reset the LTFT before each log file. The can runs great and pulls really good, have not seen any Knock either. Hate to mess with it too much, but would like to get the fuel trims back in line. Any suggestions?

So when you say with and without MAF, I assume you are somehow disconnecting the MAF, is this correct?

Putting Headers on the car will make it breath better and will lean the stock tune out. That is why you are seeing higher than normal Trims. With the MAF operational, you are running mostly off the MAF table with some transient correction from the VE table during accelerator pedal up and down events. With the MAF inop, the PCM will revert to Speed Density and will now begin fueling solely from the VE table. So my take on the whole situation is OEM MAF calibration is about where it should be but they have a tendency to set the stock VE table a bit richer as it is the "protection" when the MAF fails (same as disconnecting it) and is elevation sensitive. That is why the VE trims are a bit lower (still too high in my books) than the MAF readings.

Ed M

[JLowe5700]

So when you say with and without MAF, I assume you are somehow disconnecting the MAF, is this correct?

Putting Headers on the car will make it breath better and will lean the stock tune out. That is why you are seeing higher than normal Trims. With the MAF operational, you are running mostly off the MAF table with some transient correction from the VE table during accelerator pedal up and down events. With the MAF inop, the PCM will revert to Speed Density and will now begin fueling solely from the VE table. So my take on the whole situation is OEM MAF calibration is about where it should be but they have a tendency to set the stock VE table a bit richer as it is the "protection" when the MAF fails (same as disconnecting it) and is elevation sensitive. That is why the VE trims are a bit lower (still too high in my books) than the MAF readings.

Ed M

Thanks Ed. Yes, the MAF was just unplugged.