I need a competent answer before I tear into the opti again.

Background:
1) AT1 - ATI 8# on a 383, LT4 heads, mild cam, etc. 6-speed.
2) Below 4500 the car runs crisp and very responsive. No idle problems or hesitation.
3) Air-Fuel ratio is established in the low 12s throughout the powerband during WOT.

Problem Statement:
1) Occasionally (more often than not), above 4500, there is a hard drop off in power. Stumble, and not so often, dead-in-the-water.

2) Car resumes normal (below 4500 rpm) afterwards.

3) Replaced Opti cap/rotor
4) Replaced Coil (MSD)
5) Replaced ignition module
6) New Autolite 103 plugs
7) New Ignition wires

Pondering:
Since this is a 1996 with the vented opti, am I experiencing, through boost, a fluttering or other opti malfunction due to the high pressure being stuffed backwards into the opti? Should I plug up the vent line?

I am confident that the programming component is okay, as the car was previously running very good and then began its deterioriation.

 

the opti vent return line should have a one-way valve to prevent reverse flow of air. The blue side of it should face the intake and the white side, the opti. the other (feed) line should be somewhere after the MAF.

If your MAF is on the non-pressurized side, there should be a good vacuum in the intake at idle, pulling air through, and no flow at WOT because the one-way valve should stop it.

If your MAF is on the pressurized side, you willhave a better flow of air through the opti at idle. At WOT, the air should be equalized and no flow should take place (this is the way a N/A opti works).

In either case, it should not affect the way the opti works. If you do NOT have a one-way valve on the opti return line (the intake side) and your opti feed line is on the non-pressurized side, you will have a backflow of air. I'm not sure how this would affect the opti in terms of performance though.

 

Another way to look at it... with the Opti air supply line in the stock location, right before the throttle body, and the vacuum line in the intake manifold, the flow through the Opti will be determined by the differential pressure accross the throttle body. At WOT, there will be very low flow, since the pressure on both sides of the TB will be roughtly equal. At idle and low loads, the flow will be similar to a N/A application, because boost is very low.

But, when you are under boost, the Opti is now seeing the full boost pressure, and its possible you could damage the seals, or even cause some strange motions of the rotating assembly if the pressurized air was blowing out the shaft seal.

Just a gues though.... Have you considered posting this on "Forced Induction" where people deal with this problem every day?

 

I posted a copy on the Forced Induction board too.

I am going to plug it and retest. I got a note to ensure it isn't ported to the intake manifold.

Thanks for the info.