A/C and IAC issues

[RWTD]

I have a customers 2002 Camaro M6 that doesn't want to idle at all with the A/C on. It's a very modified stock cubed 5.7. The bottom end is forged, the heads are AFR, Fast 92/92 intake and TB setup, and factory GM 85mm MAF, with a FAST Toys CAI. I don't have the cam specs right in front of me, but it is on a 110 LSA.

I started logging, and was pretty shocked at what I seen. When turning on the A/C on vehicles, I usually never seen a change of more than 20 to 50 IAC counts, and 0.5 to 1.0 on the Idle Adapt (STIT), so you can imagine my surprise when I see such a massive change. When you turn his A/C on, the IAC counts go from approx. 70-100 to climbing rapidly, pegging at 310, and Idle Desired Airflow (IDA) jumps up from 7-10 range to 20-40, and Idle Adapt (STIT) jumps up to 20-40 along with IDA. Even if you manage to get the engine to idle at Commanded (900 to 1000 rpms for testing purposes), the trims and IAC stay pegged.

Obviously the A/C compressor is drawing a TON of torque from the engine. I wonder if it is potentially going south, or has gone south, even tho the system is blowing very cold air?

Possibly I'm missing something here. Please ask any questions that may help you in your thinking.

[mowton]

Oh, I can't believe this is still available........it's easier for us if you post your tune and logs

What is the Idle AC Air and Idle Base air logging at? How are the AC Torque tables? stock?

[Frost]

That kind of load would seem to favor a compressor or A/C system issue.

[eficalibrator]

Most A/C compressors require about 10-14hp to run, so that can translate into a significant amount of additional airflow at idle.

Make sure you have enough torque reserve built into your spark advance values near idle as well. You NEED to be well back of MBT timing at idle in normal conditions so that you can instantaneously increase engine torque to offset the sudden addition of the A/C compressor, p/w pump, alternator loads, or transmission.

Lastly, I've found that a LOT of aftermarket or ported TB's don't bias enough airflow toward the IAC. This makes the same IAC position equivalent to a much lower actual airflow than what you would have gotten on a stock TB where air easily enters the IAC passage.

[mowton]

Most A/C compressors require about 10-14hp to run, so that can translate into a significant amount of additional airflow at idle.

Make sure you have enough torque reserve built into your spark advance values near idle as well. You NEED to be well back of MBT timing at idle in normal conditions so that you can instantaneously increase engine torque to offset the sudden addition of the A/C compressor, p/w pump, alternator loads, or transmission.

Lastly, I've found that a LOT of aftermarket or ported TB's don't bias enough airflow toward the IAC. This makes the same IAC position equivalent to a much lower actual airflow than what you would have gotten on a stock TB where air easily enters the IAC passage.

Greg, quick question, what is the best way to determine if you are around the MBT at idle? I know how to do that on a dyno. I have heard "the best MAP" but I am not sure if that means high or low kpa?....hopefully this isn't a stupid question.

Thanks,

Ed M

[jimmyblue]

It seems to me the A/C state is demanding excessive
air beyond what satisfies idle. This may be from the
drag torque model. That looks at A/C pressure and
IAT. Maybe one of these is giving readings that push
harder than reasonable. Like an A/C overcharge, a
semi-plugged orifice tube (?) or just a heat-soaked
IAT.

[INTMD8]

Check the a/c pressures to make sure the system is not overcharged as well.

[RWTD]

All if this is excellent advice, everyone. I truly appreciate all the replies, and I'll let my friend know so he can start working on to resolve this (it's somewhat long distance tuning right now, so I'm not there in person to help him at this moment).

[rnl35thss]

Any resolution to this? I have a very similar problem. Same 02 M6 Fbody. Not modified as much.

[RWTD]

No, so far nothing. We're thinking it's the compressor, but he's trying to find one to borrow to test, otherwise he just wasted a lot of money! We're also going to try another TB.

[rnl35thss]

Mine was in the tune. Just about got it. Good luck with yours though.