94 Grand Prix - 3.4L Lower Manifold

[Makman]

Thanks for the great website - am a little new to the site, but have an potentially interesting problem. Car has been running very rough, and spray test shows intake leak - figured it was a Plenum gasket leak. After removing Plenum, found old but pristine mounting gasket. Further inspection of LOWER manifold SEEMS to show two (2) holes, one in front of Plenum mount, one in back of Plenum mount, that go down (vertically) into the manifold. They seem to be mounting bolt mounting locations - both essentially under the fuel rail. On front side of Plenum between Passenger side injector and middle injector, rear (firewall) side of Plenum mount, is between middle and Drivers side injector. Does anyone know if these are indeed lower manifold mount locations, with missing bolts? The local dealer says he has nothing that's explanatory enough to show these bolts, or the bolt pattern, so we ordered two (2) manifold bolts with conical washers. Also, the big Chilton's doesn't even show the manifold bolt tightening sequence (Haynes is for S**T), SO - can anyone help...??? Thanks.

[93luminaz34]

Those holes are used to pull down the lower IM so that the bolt holes line up with the bolt holes in the heads. You take 2 of the lower IM bolts, and a couple stacks of washers, and tighten them down until you can make the IM mounting bolts. Hope that makes sense. You wouldn't get an intake leak from there.

[Makman]

94 Grand Prix - 3.4L Manifold

Thanks for the reply, Matt. I actually called California that night, talked to a Service Mgr there. Hey checked the book for me and actually called back the next morning, with the same info. I had ordered the bolts from the local GM guy (very $$$), but they are really helpful in setting the manifold back down - not so much for placement, but for torque process; you can get a good downward torque before you torque all the perimeter bolts down (there's actually a Service Bulletin for the 3.1, which I used on that one) which wants you to torque those downward bolts down fully before you torque the perimeter ones on the angle. This 3.4L manifold is smaller, as you probably know, so is a bit easier. The manual calls for these two vertical bolts to come out after the torque process - though I don't know why - possilbe heat transfer? And, the two holes actually each go into a casting void, but they can be bottomed out, so if anyone uses them, be careful of the lengh of bolt you use - that's why I ordered mine from GM - they fit and worked perfectly. Thanks again.