Originally Posted by
Paintbytony
99 5.3 swapped into a 69 nova, stock motor rebuilt and 4l60e. So the base tune is good but RPMs dropped heavily and has a high/low surge when the A/C came on so I increased the idle speed upon A/C request by 200 RPM, this helped some but after about 10 minutes of idle the motor started smoking real bad (rich condition) I quit for the day and downloaded 2 similar files to compare and found +- 10 points variance in only a few tables, this morning I pulled all spark plugs and only 2 plugs were fouled ( the 2 rear plugs on opposing sides ) strange! I ran a compression test (130 +- 5 across all cylinders) did a leak down check on cooling system, it held -15 psi for 20 minutes, swapped injectors on passenger side and did a positive pressure smoke check on intake plenum with 8psi and found no leaks. Data log did show a strange increase in total advance when A/C engaged increased number to 46 degrees advance timing. Loaded my second tune back in the car and she runs good again, no smoke, plugs look good now but still have the surge and now I ask....
1. Why did it only foul the 2 rear plugs on opposite sides?
2. Why was the computer commanding 46degrees advance timing
3. what do I need to tune to stop the "surge" when A/C is engaged