I've got about 1500 miles on a rebuild I did myself. The motor runs great and there are no problems that I am aware of, but the S-AFC always reads -760mmhg. Never has it moved from the max vacuum reading of the sensor. I've replaced the vac line and sensor. (first thought the line was too restrictive and that did nothing so I threw on an extra sensor)

I've seen air flow rates over 60% and the motor is heavily street ported, with the rats nest removed, but the vacuum never drops even at sustained WOT in high revs.

I'm going to try pulling the air filter and see what happens. Its a newer cone filter with less than 3K on it, so I wouldn't think it could be clogged yet. Then again who knows....

Anyone else have this experience?

 

get a real vac gauge, and hook it up, what does 260mmhg convert to in PSI, theres no way your car is under -20 vac at WOT............

 

760 not 260.... Roughly 1.1bar of vacuum

There are no vacuum accessories running off the motor. No BAC, ACV, none of the vac solenoids are hooked up... Only things attached to the manifold are the crankcase (direct PCV. no valve), FPR, pressure sender, and OM jets....

I suppose its possible that my air filter is messed up from being wet once. Its never choked the motor out though. If it wasn't snowing I'd go mess with it right now.

I'm gonna dig into the FSM now and see what the manifold vacuum should be.

 

umm.. the Sacf isn't hooked into you boost sensor....

you should be reading boost / vacum off a boost gauge.

 

This is an N/A application. I figured out from the FSM that the voltage stays constant depending on what range of atmospheric pressure is applied. (low altitude vs high)

 

dude I already told you. it's not even hooked up the afc. if it is unhook it LOL... that reading is for if you have a mapped bassed system (FDs) which use only the pressure sensor instead of the AFM.

 

OK, that's not actually possible, plus your conversion's a bit off. -760mmHg (-1.01325bar) gauge pressure is absolute zero pressure and is physically impossible to achieve. That should've been your first clue...
It's reading that because you have the S-AFC set for MAP sensing instead of an AFM. It's not even supposed to be connected to any pressure sensor on FC's. You need to have another read of the manual and set it up right.