EFI Tuning Philosophy

[Foghorn]

Hi All. New Dominator EFI install. I just recently got it running and idling, with the accelerator pump tweaked to eliminate the lean condition immediately upon opening the throttle.

My installation has side pipes with ~ 38 inches after the collector and WBO2 sensor, and the collectors are slipfit as well - lots of compromises in the exhaust system.

I started with one of the Holley pre-configured tunes and modified the ICFs as necessary. I have a warm fuzzy that the system is working as advertised.

I'm expecting a false lean signal due to my exhaust configuration. So far, the plugs are showing waaaay rich at idle & cruise conditions. My Target AFR in both is 14.2 & 13.8 respectively. I started it richer than that and the plugs fouled within 10-15 minutes.

Is it acceptable from a tuning standpoint to keep leaning the Target AFR table until the plugs read like they should (i.e. light brown instead of black & sooty). I'm good with using Kentucky windage to hit my target, I just want to make sure that I don't introduce an unforeseen problem or situation with the EFI/ECU due to leaning out the Target AFR table until the plugs look good. Thanks!

[andrewb70]

Is this a Corvette or Cobra? Either way, cool!

Ideally, you want to seal up the exhaust so you don't have to fudge the Target AFR table. The reason being is that the amount of leakage in the exhaust is probably not consistent and will change as the temperature of the exhaust changes.

I believe there's a thread floating around discussing slip-fit collectors. I think a high temp RTV product can be used to mitigate the leaking. As for the 38 inches after the sensor, that's fine. If I can be of service with the tuning, please let me know. Andrew

[Danny Cabral]

I believe there's a thread floating around discussing slip-fit collectors. I think a high temp RTV product can be used to mitigate the leaking.

https://forums.holley.com/showthread...4840#post94840 (Related Forum Post)

[Foghorn]

Andrew & Danny, thanks for your answer. I know that the right way to fix this is to seal up the exhaust system, but that isn't a viable option. I'm not in a position to try to glue the collector together. The level of effort required to disassemble and re-assemble the individual pipes that fit into the collector has me willing to pursue alternative means to get the AFR where it is supposed to be. At risk of sounding lazy, it's not that, it's that it took extraordinary effort to assemble the side pipes almost eight years ago, and I'm worried that I won't be able to separate them without damage to the pipes. I'm fully aware of the dangers of the engine leaning out on the top end under load. The Holley EFI has ways to prevent that from coming to fruition due to an erroneous sensor input. I'm willing to give up a little power on the top end to keep the mixture safe. It's a street car and will only see WFO rarely.

Back to my original question: It's so rich during its normal operational areas that it's fouling the plugs. Unless I'm going to put the ECU in a position that it can't calculate correctly, why can't I tune around the known short-comings of my exhaust system? Thanks!

[Danny Cabral]

So in the Closed Loop Parameters screen (System ICF), program your Global File to run in Open Loop mode at low RPM (when air leaks into slip-fit headers - lean contamination of WBO2 sensor), and run in Closed Loop mode at higher RPM (when exhaust blows out of slip-fit headers - not contaminating WBO2 sensor). Remember, the wideband O2 sensor is an oxygen sensor, not a fuel sensor.

[Foghorn]

Thanks, Danny. That makes sense.
EDIT: Do you have any links to tuning in Open Loop? If I understand correctly, Open Loop doesn't reference the WBO2. So changing the Target AFR and letting the ECU modify the Base Fuel Table will be replaced with me changing the Base Fuel Table directly? I'll do a search of the forum and read the manual, but any clarification would be appreciated.

[Danny Cabral]

You're welcome.

[AndyF]

Thanks, Danny. That makes sense.
EDIT: Do you have any links to tuning in Open Loop? If I understand correctly, Open Loop doesn't reference the WBO2. So changing the Target AFR and letting the ECU modify the Base Fuel Table will be replaced with me changing the Base Fuel Table directly? I'll do a search of the forum and read the manual, but any clarification would be appreciated.

Tune in Open Loop just like you would a carb, except your hands don't smell like gas. Hook the laptop up to the system and run the engine until the thermostat is open. Then manually adjust the Base Fuel Table in the idle area until you achieve the best quality idle. If timing is controlled by the system, then you can also adjust the timing to achieve the best idle quality. One way to judge idle quality is by watching the MAP and the IAC Position. This is the same as watching a vacuum gauge when tuning a carb.

[Danny Cabral]

Thanks, Danny. That makes sense.
EDIT: Do you have any links to tuning in Open Loop?

For manual tuning, read the "Base Fuel Table Tuning Quick Guide" in the Holley EFI software "Help" Contents (top Toolbar of the Holley HP/Dominator EFI software).

If I understand correctly, Open Loop doesn't reference the WBO2.

Correct.

[Foghorn]

Tune in Open Loop just like you would a carb, except your hands don't smell like gas. Hook the laptop up to the system and run the engine until the thermostat is open. Then manually adjust the Base Fuel Table in the idle area until you achieve the best quality idle. If timing is controlled by the system, then you can also adjust the timing to achieve the best idle quality. One way to judge idle quality is by watching the MAP and the IAC Position. This is the same as watching a vacuum gauge when tuning a carb.

Thanks Andy!

For manual tuning, read the "Base Fuel Table Tuning Quick Guide" in the Holley EFI software "Help" Contents (top Toolbar of the Holley HP/Dominator EFI software).

Thanks Danny!