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on-AC stuck at 85 steps

 
Old Aug 16, 2017, 05:03 PM
  #1  
Rom
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on-AC stuck at 85 steps

Hi all,

Following on from my other thread where I was just looking for the maximums, my next issue is that the ISCV seems to be stuck at 85 steps when AC is on (and engine is warm) no matter what else the engine doing (revving, power steering usage, etc). With AC off the steps vary with demand, but with AC on the steps get set at 85 and won't change, even though demand DOES vary.

I've checked all the tables I can find that control the ISCV but nothing seems to make sense. The ISCV lookup table says that 67% demand to set the ISCV at 85 steps, but demand with AC on can hit 90%+ but the steps do not increment (even though the ISCV lookup table has much higher numbers for >67%).

I'm at a loss as to what is setting the ISCV to 85 with AC on. The initial step count table is >140 steps with AC on, but it seems to be ignoring that table altogether.

Does anyone know exactly what tables are looked at on the 8859 Evo 9 rom when AC is on? As far as I knew varying demand should at least vary the steps no matter what, so this is strange.

With AC off everything works normally with steps varying based on demand.

Thanks,

S.
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Old Aug 18, 2017, 12:44 PM
  #2  
Rom
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Hi all,

I just did another test where I raised the entire ISCV lookup table by 20 steps (every single cell, except zero-demand which I left at zero steps). Started the car up and the car idled at a very high 2000rpm (expected) when warm. The steps were much higher, showing around 80 steps at "normal" idle (since I raised it), so again, exactly as expected.

Then I turned the AC on.. and the darn thing went to 85 steps again! I would have expected 105 steps, but no, again 85! The idle was about 1700rpm, but that's because timing advance was much higher overall (not sure if it would have eventually settled back down when the trims adjusted), but basically going from 2000 -> 1700 rpm is a similar drop I have when the ISCV table is at its previous values (1100 -> about 800).

Anyway, I guess I need one of two things:

1) on-AC timing advance - is there a table for this??
2) Why would it be fixated on 85 steps on-AC? I don't see any reason for this in the tables I have (from the ISCV disassembly thread). Is there any other table that could be doing this?

Any one have ANY ideas about this?

Thanks in advance for any insight!

S.
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