Dan Sarandrea (Phila)
Waitin' On Parts...
The first time assembling the manifolds to the head, I noticed it was very easy to just hang the three parts (exhaust manifold, two intake runners) onto their mounting studs protruding from the head and tighten the nuts, only to find that there is enough range of motion for the intake runners to be tightened up and come to rest in such a position that the plenum would not sit down onto the four mounting studs coming from the two runners.
So now when assembling the manifolds to the head, I find it very helpful to simply place the FI plenum onto the four studs sticking out of the two pairs of intake runners, which ensures proper orientation/alignment of the intake runners, and then tighten the seven manifold retaining nuts. Once the manifold nuts are torqued, I just pull the plenum off the studs and continue with assembly until it's time for the plenum to go on permanently.
Not sure if any of that helps, but it might if you think that there's a leak where the intake runners meet the head or the plenum.
Speaking of potential spots for vacuum leaks, did you inspect the hard plastic ("bakelite") injector mounts and replace the rubber O-rings between said mounts and the FI runner castings, as well as the O-rings between the injector noses and the inner part of the injector mounts?
So now when assembling the manifolds to the head, I find it very helpful to simply place the FI plenum onto the four studs sticking out of the two pairs of intake runners, which ensures proper orientation/alignment of the intake runners, and then tighten the seven manifold retaining nuts. Once the manifold nuts are torqued, I just pull the plenum off the studs and continue with assembly until it's time for the plenum to go on permanently.
Not sure if any of that helps, but it might if you think that there's a leak where the intake runners meet the head or the plenum.
Speaking of potential spots for vacuum leaks, did you inspect the hard plastic ("bakelite") injector mounts and replace the rubber O-rings between said mounts and the FI runner castings, as well as the O-rings between the injector noses and the inner part of the injector mounts?