'05 M6 GTO E40 AC Tuning with big cam

[C10Racer]

I've got a '73 Camaro we've just finished installing an '05 GTO LS2 in with the OE E40, T56, Patriot Headers, full dual exhaust with SpinTech mufflers, a simple CAI, LS7 springs/lifters and a Comp 54-600-11 Thumpr at .553/.536 and 219/233 @ .050 with a 109 LSA (I know ). We had a very good local tuner-tune the car before the Vintage Air system was finished (Sanden 6-piston compressor) and with the AC off the car is great. The signal from the Vintage Air Trinary pressure switch goes back to the E40 to tell it that the AC is on and the signal is being received because the ECU turns on the third fan relay to run both GTO fans at full speed.

1)If you turn the AC on with the car at idle its ok most of the time and settles around the minimum idle speed of 950 after a single light surge down to roughly 850 RPM
2)If you coast down either in neutral and/or with the clutch in as you come to a stop the vehicle with surge 3-4 times then die; if you coast down in first with the clutch engaged and clutch-in just before stopping it'll surge 3-4 times from 750 to 1050 then settle down around 950.
3)If you blip the throttle lightly from a stop and let the clutch out lightly to move around at low speeds as soon as you clutch in the motor surges heavily 3-4 times then dies.
4)Application of throttle can help with any of these issues but that is not really acceptable with an FI car!

I am trying to avoid modifying the AC-disengaged idle because its perfect but with this particular ECU I can't find any parameters that really modify the idle/coastdown dependent upon AC input and also there is no Stall Prevention option on this setup.

I have added 2 then 4 then 8 lbs/hr of air in the Final Idle Airflow Minimum table in first/reverse and neutral between 400 and 1200 RPM and while it has helped the issue slightly I end up with more surging at idle with the AC on. The Engine>Idle>Airflow>AC Airflow tables only effect idle in the moment the AC turns on or off based upon how I'm reading it and beyond that there don't seem to be any tables related to Idle/AC state.

Am I missing something? If I'm not missing something what is the best option available to try and remedy this issue? I have tuned Carbs/ Mechanical Fuel Injection and L31 systems with the old JetDST/TunerCat but theres always been a provision for adjusting idle specifically related to the AC system state.

The tune is attached so someone smarter than me can see if they can figure out what I'm missing! I plan on tuning or fine-tuning numerous LS swaps/L31s/Ls powered OE vehicles so for some reason I figured I'd pick the most frustrating to start with!

[13qtr]

I got the exact same thing in my goat. Haven't got it sorted out either... big cam NA. Hope someone chimes in.

[C10Racer]

I got the exact same thing in my goat. Haven't got it sorted out either... big cam NA. Hope someone chimes in.

I've always kind of thought if you could make a certain setup idle with a carb you could make it idle with EFI but the E40 ECU may prove that theory wrong. I simply can't believe there's no way past this; with enough timing and enough fuel there's got to be a way.

[Lakegoat]

How did you set up your fuel pump? Fuel pressure? Return system or no return? Any change in injectors? Are you still using the maf?

[C10Racer]

How did you set up your fuel pump? Fuel pressure? Return system or no return? Any change in injectors? Are you still using the maf?

Runnnng a Tanks Inc tank and PA-2 Pump, a C5 Corvette fuel pressure regulator/filter assembly with the return there, stock injectors and still using the MAF.

[Lakegoat]

If you have 58# of pressure, your stock injector info should be good. I noticed that your Primary VE table was quite a bit higher than mine and your Base Running airflow is lower. My cam is a 114+2 but it is a 228/235 and I had a 233/248 in there recently and ran about the same. Look at my Spark Timing, Base and Coastdown and try that and see how it does. Change your base running airflow to match. Disregard anything else as this is a blower tune, SD.

[Lakegoat]

If you are doing some wot throttle, I would lower the low octane spark table about 4-6 degrees too so if it knocks, it has somewhere to lower the spark.

[C10Racer]

If you have 58# of pressure, your stock injector info should be good. I noticed that your Primary VE table was quite a bit higher than mine and your Base Running airflow is lower. My cam is a 114+2 but it is a 228/235 and I had a 233/248 in there recently and ran about the same. Look at my Spark Timing, Base and Coastdown and try that and see how it does. Change your base running airflow to match. Disregard anything else as this is a blower tune, SD.

Thank a ton for the help; I am working on a a better base tune using you advice and the changes I've made based upon your info have all been positive! Guys willing to take their time to share make this stuff so much easier! I ended up finding a "silver bullet" for this issue and will post about that below.

[C10Racer]

Alright, so I started working on a tune based upon Lakegoat's advice but stumbled upon something else that has helped immensely. In Engine>Torque Management>AC Torque you can adjust AC compressor torque compensation based upon both IAT and AC Pressure. Basically the ECU dials in a pre-specified amount of torque compensation based upon the above stated parameters and RPM. I ended up more than doubling the torque compensation tables in the relevant areas which with the big 6-piston Sanden compressor made a huge difference for my setup. I also setup the cooling fans where they come quicker and harder to keep the AC pressures down. Thanks a ton guys

NepLuna '73 Camaro LS2 7-15-17 AC Pressure Mod3.hpt

[dankmac]

Do you have a BCM or just the E40 Ecu? I didn't think there was any way to tell the E40 without a BCM that the AC was on. I struggle with the same AC surging and would LOVE to find a way to smooth it out.

Where do you wire the trinary switch into the ECU?