EFI Idle Tuning Notes

[steve69ss396]

Awesome! I see that as an option. I'll give it a try! Thanks!

[Danny Cabral]

You're welcome.

[allan5oh]

I'm running a Dominator ECU on my 427 SBC with an F2 ProCharger on E85. The cam is 274°/286° @ .050" with 108° ICL, 112° LSA and 0.704" lift. It idles at 1400 RPM and I can't get the IAC anywhere near the recommended percentage. Can the Dominator use Alpha-N for idle below a certain RPM/TPS and switch to Speed Density mode above this point?

This is going to sound nuts. Your cam isn't that big. Alpha-N isn't needed. Cylinder to cylinder balance has a larger effect on idle quality than cam size. I've done more than a few engines with cams that size or larger, and they work fine in VE.

[Cougar5.0]

Speaking of larger cams, I thought mine was moderately large (250° @ .050", 110° LSx 9" vacuum at 950 RPM), so I wasn't all that surprised when the car surged badly on initial startup with the Holley. It was still surging moderately after some Learning. (I used the 454/245/48# template, but mine is a 427 so a bit over-fueled). Injector pulse endpoint tuning and getting the IAC down to about 8% at idle (was 30%.) But apparently one parameter not discussed in the (very helpful) 1st post was causing the surging issue that was laughably bad, once I took the car for it's first drive with the Holley! It was even surging during deceleration (was bordering on dangerous going downhill as the car was accelerating on it's own about every second.) <- And this was the clue that I needed. When using a 2-wire Ford IAC (set to PWM-), the Holley defaults to a frequency of "1". D'oh. I design PWM controlled power supplies for a living, yet I assumed that the default value "must be fine". I've since read that the Ford typically wants 300Hz or 600Hz depending which source you read. Being a typical car guy who wants instant results and will change things just to see what happens, I upped the frequency to just 10Hz and the car suddenly idled solid as a rock! I can actually accelerate at as low as 1700 RPM in 3rd or 4th with minimal load on the engine. The "big cam" bucking and misfiring at light load cruising that I had before with the (carefully tuned) OEM ECU (up to 3K RPM) is now mostly gone. Not bad for my 1st day tuning with the Holley.

EDIT: Well geez, today I learned there's an Idle ICF for a Ford PWM IAC called "5L Ford PWM IAC.idle". Pretty cool, though learning some stuff through experimentation was kind of interesting.

[steve69ss396]

Finally tried Alpha-N "Combo" Load Sensing in Engine Parameters. Alpha-N kicks in under 1,600 RPM & 3% TPS. Cold & hot idle are better. Before, the Learning would be +20% at idle and the next time -20%. The ECU was chasing the tune, it would idle around 85 kPa and I'm 100 feet above sea level. Sometimes it was good and other times it was bad. It would idle OK, but not as good as when it was N/A with a carb.

[Wrenchhead67]

Hi Danny, thank you for posting this. My Base Fuel Table does not follow this pattern, and I don't think it is idling its best. I know EFI idle can be smoother than a carb, but at idle, it just does not seem to have a consistent pattern.
For me to find what the engine needs and get the best idle, I've used a vacuum gauge in the past (just like with a carb). If I do this with the EFI, I think I'd need to:
1) Plug IAC and disable Learn during idle (just to exclude outside variables).
2) Adjust AFR to get the highest vacuum reading (the ECU would be adjusting the LBS/HR to hit this, correct?

Say I find my combo has the highest vacuum reading at 13.3 AFR, and that "sets" the Base Fuel Table at 0.60 LBS/HR at 850 RPM, 13.5" vacuum. I'd then place 0.60 LBS/HR in the "center" of my 9 cell grid and follow your guidance above?

Does that sound correct?

Thanks, Todd