G5X3 STFTs and Overlap Induced Errors
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TECH Apprentice
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From: Clear Lake Area, TX
G5X3 STFTs and Overlap Induced Errors I have been tuning my G5X3 114 in my GTO and have verified odd behavior that I can only attribute to overlap.
Problem: Despite being able to tune stfts at all cruising speeds...whenver I come to a stop and the car must idle for a few minutes, the STFTs start shooting up to +6 +8 +10. One can verify the 02 readings...sometimes erratic and bouncing from 800 down to 50 mV...the average tends to fall around 200 mV. The VE table is about right, but when the computer adds +8, the idle becomes very rich with a strong sulfur smell.
Initial Solution (Way Wrong): Was to follow the instructions on various boards and continue to add fuel. Unfortunately, this caused the car to be WAAAAAAYY RICH - so rich to the point it had an overwhelming sulfur odor. It seems the excess fuel was mixing with the air from the overlap and allowing the 02s to think they were now in the right range.
In addition, the rich VE made the car almost impossible to start when warm and in Closed Loop mode. It would sputter and stumble and hunt for an idle for 10-15s.
Failed Attempt to Solve
I have tried altering the switching values engine>fuel>closed 02 values to trick the computer into thinking it was not rich/lean at the low 02 mV. I didn't see much effect and was concerned that 0, 2 or 4 didn't pertain to the cells I needed.
I have already done the idle procedure outlined on LS1Tech including IAC Park and MAF gm/s. Desired now matches actual very nicely.
I have tuned my VE to within +1/-1 at all values outside of idle and when the throttle is abruptly closed.
Proposed Solution
At this point, I think I need to find a way to disable ST Fuel Trim Correction when speed = 0. Does this parameter exist in the HP Tuner software?
Can I modify the Closed Loop Proportional Idle Control Tables to net the same effect - no Trim correction when below a certain speed?
Otherwise, I think I am cursed with the PCM dumping raw fuel into an otherwise good mixture any time the cam is causing overlap.
Problem: Despite being able to tune stfts at all cruising speeds...whenver I come to a stop and the car must idle for a few minutes, the STFTs start shooting up to +6 +8 +10. One can verify the 02 readings...sometimes erratic and bouncing from 800 down to 50 mV...the average tends to fall around 200 mV. The VE table is about right, but when the computer adds +8, the idle becomes very rich with a strong sulfur smell.
Initial Solution (Way Wrong): Was to follow the instructions on various boards and continue to add fuel. Unfortunately, this caused the car to be WAAAAAAYY RICH - so rich to the point it had an overwhelming sulfur odor. It seems the excess fuel was mixing with the air from the overlap and allowing the 02s to think they were now in the right range.
In addition, the rich VE made the car almost impossible to start when warm and in Closed Loop mode. It would sputter and stumble and hunt for an idle for 10-15s.
Failed Attempt to Solve
I have tried altering the switching values engine>fuel>closed 02 values to trick the computer into thinking it was not rich/lean at the low 02 mV. I didn't see much effect and was concerned that 0, 2 or 4 didn't pertain to the cells I needed.
I have already done the idle procedure outlined on LS1Tech including IAC Park and MAF gm/s. Desired now matches actual very nicely.
I have tuned my VE to within +1/-1 at all values outside of idle and when the throttle is abruptly closed.
Proposed Solution
At this point, I think I need to find a way to disable ST Fuel Trim Correction when speed = 0. Does this parameter exist in the HP Tuner software?
Can I modify the Closed Loop Proportional Idle Control Tables to net the same effect - no Trim correction when below a certain speed?
Otherwise, I think I am cursed with the PCM dumping raw fuel into an otherwise good mixture any time the cam is causing overlap.
