Well, I finally got some old retainers and no more leak! The clips keep the injectors in the right spot in the fuel rail so that a perfect seal is made. However, you can get away with no clips on 7 of the 8 injectors but the one last injector, on the passenger side closest to the firewall, MUST HAVE A CLIP (TPI engines). The reason is simple. That injector sits right at the foot of the fuel inlet hole. Thus, the pressure at that injector is greater than the rest of the rail. So if the injector is not seated right, it will leak and cause a nice explosion when you're least in the mood for one. Anyway, thanks to all of you who helped. By the way, it seems that a couple of the upper runner bolts went south on me during re-assembly. That is to say, they won't tighten down, I guess I over toqued them, but it really didn't feel like it. Anyone think that would cause a vacuum leak? Of the 8, 2 were on the passenger side (courner closest to the throttle body and lower middle) and one on the driver's side (lower middle.) It seems to be locked into place very firmly with its gasket and all the others are nice and tight.

Hence the reason I tell people to use them. Some are lucky, some dont need them (tolerances suck that bad).

About your question... depends on if those holes are blind holes or not, meaning either they are open to the plenum (not blind) or they arent (blind).

I think they would be blind. I don't think that the bolts protrude into the plenum, if that's what you mean. So what then?

Should be no leaks then, unless the holes are so bad that the bolt isnt holding the parts together with enough pressure.

Those bolts if not drawing down can definitely be the source of a vacuum leak. And I doubt if you have to ask me how I know.

Been there and done that, got that hand stamp and T-shirt.

No such thing as pressure on one injector higher than another. Even if the fuel ral was 600 feet long, the pressure would be identical at one end as the other.

As for the plenum bolts, what should I do? How can I seal those? If I were to dip the bolts of the ofending bosses into silicon and then plug them in, would that work? I DO NOT want to take this thing apart and get a new plenum - that might have the same problem. There's got to be a way to fix this

Since that injector sits right at the inlet hole the fuel will slip past the o-ring if its not in the right spot. The clips, whether locked or not, will keep the injector from going too high up into the rail where there is less of a seal. That's why when I had the rail and injectors installed without clips, only that one injector (which sits right at the fuel line opening - passanger side closest to the firewall) would leak. Without the clips, when the rail is tightened down, the injector will be pressed higher into the rail than it should be - hence the leak.

Can't think of any other explanation since as soon as I installed the clips, the leak stopped.

Either larger bolts or a heli-coil as far as I know. Sometimes the same diameter but a longer length will work as well.

Sorry to be the bearer of bad news....

You may be able to tap the threads for 5/16 coarse thread (-16? )as opposed to the metric that is in there and have it hold. I've done that. Factory is 8mm IIRC, I think 1.25 pitch but not sure. Heli-coil if you want to repair it, works good but the repair kits are not cheap.

If you want a permanent repair that'll last, a heli-coil is the only way to go. Any aluminum part on a car is notorious for losing the threads. In fact, if you look at any high dollar aluminum race parts, like heads, a lot of them have helicoils installed in all the threaded holes when they're brand new. Aluminum is so soft and porous, even when you're really careful tightening bolts, all it takes to strip the threads out is installing and removing the bolts a few times. The aluminum intake on my 69 camaro has helicoils in both the thermostat housing holes and all four of the carb stud holes. It really sucks when you unscrew a bolt and have all the aluminum threads still wrapped around the bolt! Helicoils are really simple to install too. It says on the package what size drill bit to use, and they supply the special tap and insert tool with the kit. I usually put a couple of drops of red loctite on the insert before I install it too just for good measure. Helicoils replace your soft aluminum threads with nice strong steel threads. Just my .02.

Does anyone have a good GM part number for the retainer clips?