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Tune to make A/C work after heads/cam install (EFILIVE)

 
Old 08-05-2016, 06:11 AM
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Default Tune to make A/C work after heads/cam install (EFILIVE)

I just installed new engine/trans with LS6 intake/LS6 heads and a custom grind cam. I have it tuned to drive pretty well but if I am driving with the ac on and push in the clutch or let off the throttle the car just dies. I am assuming it is idling down and it just can't hold the idle so it dies.

I know someone told me a somewhat cheat way to go in and up some values by 25% until it doesn't die but I am looking for the more correct way of getting it to work.

I have efi live tuning software.
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Old 08-05-2016, 01:00 PM
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There is some stuff about the A/C drag torque and adding
air for compensating it. That really gets bent when your
low end VE table becomes unrealistic (like lumpy cams
cause) and so does the delta torque per delta air (or
vice versa) model that lies behind that and (at least in
HPTuners) I don't get to see (and wouldn't have much
idea how to fix anyway).

The other things to look at are:

- is idle mixture on entry to that mode (i.e. before trim
pulls it back, presuming you're still closed loop) too fat,
which always destabilizes idle RPM loop control?

- Is your idle advance too low (my van is low teens vs
cruise in the 20s - 30s) given the punked low RPM mixture
(cam again)? My car is to worked over for me to remember
what factory-normal does anymore.
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Old 08-05-2016, 03:55 PM
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Originally Posted by jimmyblue View Post
There is some stuff about the A/C drag torque and adding
air for compensating it. That really gets bent when your
low end VE table becomes unrealistic (like lumpy cams
cause) and so does the delta torque per delta air (or
vice versa) model that lies behind that and (at least in
HPTuners) I don't get to see (and wouldn't have much
idea how to fix anyway).

The other things to look at are:

- is idle mixture on entry to that mode (i.e. before trim
pulls it back, presuming you're still closed loop) too fat,
which always destabilizes idle RPM loop control?

- Is your idle advance too low (my van is low teens vs
cruise in the 20s - 30s) given the punked low RPM mixture
(cam again)? My car is to worked over for me to remember
what factory-normal does anymore.
Some other things to add to the list:

How high is your idle set with AC on vs AC off? I set mine to +150. THe typical +50-75 wasn't holding. Keep in mind cammed engines have LESS idle torque than stock cammed engines. You need some RPM to overcome the AC compressor load.

If it's dying right when you clutch and let off the gas, this can indicate you need some more follower air - or at least a follower delay of 2-3 seconds. This will "hang" the idle around 1200-1400 rpm for a couple of seconds and then gently settle to idle. You may also need to add a lot of follower air in addition to the delay.

Depending on the year and OS, you may have "AC on" row for base idle air or you may just have base idle air with an AC offset. The AC offset will likely be a negative number, but require a minimum of zero (never less air than AC off). The max offset value is likely something low like 2.5. Change this to 5 or higher.
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