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Car is a 1991 SPG- 173K, K&N, IC fan, 2.5in hi-flow-cat-back, tweaked APC, Brad's AID
I know a fair amount about APC operation, but this is either utterly puzzling or related to something else. In 2nd gear, boost climbs normally to 15 psi, then immediately falls back to 9 or 10, and stays there, maybe less, for the duration of the acceleration (thru 3rd, 4th on choice stretches). I would normally see this as knock as my fuel setup is stock (I can elaborate on this if necessary, but suffice to say that the highest power levels are achieved this way with the current setup on this particular car), but if I roll into boost in third or higher, only very rarely does the same behavior occur. If I do get this mysterious boost cut in the higher gears, boost climbs back up again as is normal APC operation.
Pertinent Info:
Ignition is good: recent cap and rotor, Magnecors, 7EVs, timing 18DBTDC
All turbo plumbing is good except a small leak that I cannot find
Fuel filter replaced 6 mo. ago, fuel pump is _original_
APC equip has been gone through by an exp tech 3 mo. ago, KS is _original_
Pending HG failure, but I'm prepared for that when it gets worse, only getting pressure in coolant now.
My best guess is that in 2nd gear, something is vibrating at a knock-like frequency and the KS is betraying me. It seems weird that it cuts 6psi all at once, I have never seen this before, does anyone else lose more than 2-3psi upon APC intervention? I am totally stumped, don't really know where to start. Thank you all in advance!!
Andy
Boulder, CO
posted by 216.241....
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