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.

 

Do you have any after market ignition help? If not a msd 6a might do the trick.

 

don't plug the vent into the manifold. Let the vacuum line vent to atmosphere.

 

Did you experience a similar problem?

What were your symptoms?

I am prepared to block it off completely for now, just to see if it resolves my problem.

 

When I used the opti I ran it one night with out the vacumm and that was enough to distroy the cap and rotor.

 

Sure your cam dowel pin isn't too long?

Why couldn't you just plumb the vent line on the suction side of the blower? Seems logical to me that blowing through it would defeat the purpose...

Ryan

 

yep, just vent it to the suction side of the blower, or put a 1 way check valve on the vacuum line so's that you don't boost the opti.

 

I've had mine unhooked, and unplugged for several months without any problems(knocks on wood). But now that you mention it, I might as well just plumb it into the suction side to be safe.

 

The stock checkvalve on the harness should kep opti from boosting aslong as you moved the tube that goes on the intake to the suction side.

 

Sounds like plugs / wires to me..

Scan it look for retard other than that atleast you know it's ignition, or your fuel psi but i doubt that on #8.

 

can you get the car to experience the same troubles at 4500+ when NOT under boost? If so, it's not related to boost and the opti... might be just the opti.

are you running the vent lines in the stock locations?

 

UPDATE:
I disconnected the intake manifold line to the opti and the problem remained the same. There were also properly functioning checkvalves in line. Therefore, I am ruling out the opti for now since I had the cap/rotor replaced earlier.

However, while under the car, I noticed that my rubber elbow tube, that is between the blower (output) and the twin-intercooler splitter pipe, was severely kinked and at less than a 90 degree angle. This is due to the way the P1SC sits in the bay and the tubing for the twins, it is very, very low and appears to be kinking the tube. I pinched it and it seems to be soft.

Now, the symptoms are starting to appear familiar. Earlier, prior to the blower install, I had built a cheesy CAI and due to the sheer power of manifold vacuum, it collapsed during hard acceleration, mostly in the upper RPMs, and then the car felt like it had the stuffing knocked out of it..big power drop-off. Well, those symptoms are just like this. So, the issue is...is the rubber elbow collapsing during acceleration due to vacuum, even though it is experiencing boost at about the same time (4500 RPM)? Seems illogical, but logic has been tossed to the wind before...

 

The pinched tube is most likely restricting airflow at the higher rpms. Is the boost dropping off up high?

 

I can't ascertain one way or the other since this is a relatively new install, but the boost gauge during its run up, starts fluttering at about 4-5#s and by then the whole power curve starts to collapse. I have an 8# unit, but with the twins, I doubt I could see a full 8#s at less than 6K RPM.

We may have to build a hardened tube in lieu of the flexible elbow. But the P1SC is hard mounted to the engine and the intercoolers are hard mounted to the body, so I still need some flexibility. Gonna have to get creative.

 

I had EXACTLY the same syptoms as you. Everything building fine. AFR was fine, FP was fine and then the HP on the dyno just cratered at 4500 and the car was stumbeling and generally unsettled..

Came home. I knew I was burning oil badly form the last rebuild and the rings not seating. The problem was oil fouled plugs.

However, assuming you do not have a burning oil problem then I think your spark is getting blown out. I would gap the plugs at 35 thou.

You have an aftermarket ignition box, right? When I was first on the dyno I took the box out thinking that it might be the problem. The next run, the numbers dropped off at about 4000 rpms and it was because the spark from the stock system could not make the jump so I knew the MSD was fine.

Good luck but that is my hint to you.

My opti has vented to atmosphere for three years without problem.