70s EFI Throttle Body Replacement Gaskets

[Phil Weber]

Scott

Checked back through some older parts books and have found another gasket was used in 78-79 (# 1612942 ) . I can't find any pictures of it but I'm guessing this gasket didn't have the extra hole . This gasket was superseded to the gasket I have with the hole ( # 1619471 ) which was introduced around 1980 . There is a further supersession to # 3634798 which has been sold on Amazon (https://www.amazon.com/ACDelco-3634798-Gasket/dp/B0016HUQBE) and at Walmart. It still might be available from GM .
So here is where I'm at 

76-77 large TB *NLA*           
78-79 Small TB ( no hole ) *NLA* Supersedes to hole type
80    Small TB ( with Hole) Late number maybe still available

[79 Eldorado]

Phil,
What you wrote seems to make sense. That would explain why my car had no hole and why Bruce was not aware of the hole. His car is also a 1979. Jack's car is as well but his is a CA model and so maybe there's a caveat.

I'm shocked that there was even a listing on Amazon. It seems it's not currently available but still incredible. It also appears it's the entire "sandwich" gasket/plate/gasket.

I'm still curious about the history, the reasoning, and even if GM used the standard convention for TOP RH side. Jack's car had it in a different position and it does seem like a big coincidence that it lines-up with what seems to be specific geometry; but only if the correct position seems to conflict "Top RH Side".

Scott

[Jaks79Britz]

Hey guys - I re-installed TBI today (along with new fuel injectors, but I'll close out that discussion in another post later) and ended up deciding to install the gasket positioned with the TOP RH SIDE tab on the Rear LH side of the manifold (small hole over the EGR passage).  I'm going to take the car for a spin tomorrow to see if I feel or experience any issues. 

[bcroe]

I have seen ALuminum intake bores enlarged to
match the large Throttle Body on a 403, guess
it worked OK for him.  I use the large TB with
large bore iron intake on a 403, no problem. 

I guess to put the small TB on an iron intake,
someone like Scott needs to check the mating
components match up at the same positions on
the gasket.  Failing that, an extra thick plate
could have the strength to maintain pressure
over a gap. 

The extra hole was apparently introduced around
the end of the 70s EFI production, might be more
common on service replacements than on originals. 
I would just omit the hole if not already
provided.  If it is there, I'd install it as the
mfr recommended, assuming nothing like reversing
the EGR passage happened between small and large
TB.  Bruce Roe

[Jaks79Britz]

Just thought I follow up on my last post on how I ultimately positioned my gasket.  I positioned the larger tab on the rear LH side of the manifold, but I realized now that that was wrong.   

I came across an CA 80's Eldorado with the 350 EFI engine at a local junk yard was  able to pull a few parts from the engine.  I went directly to the TBI gasket and first think I noticed was that large tab was positioned in the front RH side of the manifold.  That's when I knew I installed mine wrong.  Also, noticed that there's no small hole on this one.

I thought this would be useful information for anyone reading this thread in the future.   The picture below of the gasket is how it was positioned if I'm looking at the gasket from the front of the car.

[79 Eldorado]

Jack,
That's even crazier that they had a tab but no hole. Without the tab there's no error proofing needed. There's no up versus down and there's no left versus right. Since the bolts are a different spacing you cannot turn it 90 degrees (obvious wrong but...). Anyway certainly appreciate the update.

Did you also see my question about the alternator cover? J Ward posted but his is different than mine. If you still have one on your car or if the junkyard car has one,  and you make it back, could you take a photo?

Thanks,
Scott
Edit: I forgot to ask but was the oil/gas in that cavity on the junkyard car?

[Jaks79Britz]

Yes, for gaskets with no hole, then it doesn't matter how that large tab is positioned.  Only for the ones that do that small hole like mine and over the EGR port is not the correct position!

I did see your post.  Mine doesn't have the alternator cover and I didn't pay attention to the one I saw at the junk yard.  I'll see if I can get back there this week. 

I pulled the fuel injectors off that car to have them cleaned at some point and I tried to get the fuel rail off.  That fuel inlet in the rear you had trouble removing was not budging with the tools that I had.   It was so frustrating because it was the last item that I needed to remove to get that thing off.

[79 Eldorado]

Jack,
That line goes down to the the transmission area and it just goes to a rubber line. I could access the hose clamp from the rear of the driver side wheel. I removed it without removing or even turning the wheel. So I wouldn't try to take it off the rail itself while it's in the car. Instead just remove the hose clamp.

Another thing is there's something which looks like a carrot top. That's actually factory! It's pictured in the FSM. It's slipped over the fuel line in that lower area because there's are several things which could rub so they likely wanted to make certain nothing would rub through the fuel line. That carrot was so strange I took a photo. At first I thought it was a hack-job but then I realized those "fingers" were cut so perfectly it was likely factory.

Here's the carrot:


I cut the original, not knowing it was just going into a rubber line, so when I made a replacement I used a -6AN tube nut and I put a male -6AN to hose barb in the replacement piece of EFI fuel line.
Here's my replacement line. I covered it with some wrap but it's almost too bad because I nailed the bends perfectly:


Scott