AE tuning took some huge steps forward this week. With a collaboration between Andrew (who knows Holley EFI very very well) and Tony (who last had his hands on my car on the dyno and is a very accomplished tuner) and myself we've got the old truck engine accelerating at a MUCH better pace than it has ever ran before. We've got it now where it flat out jumps any time you stab the gas in 1st or 2nd gear, but still has a bit of a lean stumble when you do the same in 4th gear. Running logs of both scenarios has shown me exactly why it's doing this and helped me even more to understand how to make the Holley run better.
By watching logs we can see exactly what is happening and when down to the partial seconds in time. Looking at the throttle position sensor, fuel flow rate, open and closed loop indicator and AFR readings we could tell that the majority of our initial issue happened when it went closed loop and the ECU tried to compensate for what the O2 was showing.
This is how I learned at first Tony had the AE turned WAY down and it was in fact doing nothing causing a huge lean spike in open loop, then as soon as it went closed loop, the ECU was dumping huge loads of fuel in trying to make up for the lean spike causing a huge fat spike. Once we turned the AE way back up and lowering the blanking value it got quite a bit better. We still had a lean spike stumble though... The next tune turned the AE up a bit more...getting it back to close what a canned Holley tune AE table looks like and it was much better again. This is when I discovered the difference between the lower gears and the higher gears.
The mistake we made on that tune was thinking it was still the open loop AE correction that was causing the lean spike when the throttle was stabbed when in fact it was more related to where on the VE based fuel map the engine was when it went closed loop once again and the ECU started to control fuel flow based on the AFR readings from the O2 sensor.
In 1st and 2nd gear, when stabbed at say 2000 RPM, the engine is at 3,000 so fast and by the time it switches to open loop that the base fuel is ready to take the ball and run with it, no issues. When I do the same stab in 4th gear, the engine is still in the mid 2000 RPM range and when it switches to closed loop the base fuel # was way low and the ECU starts compensating but it's too late.
By adding more fuel flow to the VE base fuel map where the engine is landing when it comes off AE (open loop) the ECU should be more prepared to continue dumping fuel at the rate needed without waiting for the O2 sensor and then reacting with Closed Loop Compensation. All of this happens SO fast without looking at the data you really can't tell exactly what is causing the lean spike and later fat spikes. When you log the incidents though, and learn what to look for and where...you can then make what are really pretty minor adjustments that have a huge effect on how the engine runs.
I expect one more tune from Tony should come in this evening and once I get it in the car tomorrow, I'll be pretty happy with it. Sure wish I had this tune last weekend though...maybe Chris wouldn't have gotten that win from me on his final flyer of a run...