Q-Jet vacuum and EGR questions

[MaineShark]

I'm trying to figure out what everything does, so I have a bunch of questions:

Simplest, first: how do I plug a vacuum port? I know I can put a piece of hose on, with a bolt or screw in it, but isn't there some more professional way? I'm removing my heat riser, and I don't want to leave an open hole in the side of the carb.

Next, I was looking at the EGR, up close. Correct me if I'm wrong, but is it a two-piece system? That is, it looks like there is the actuator, to the rear, and then a second part forward of that, with two pipes coming off it. One goes to the carb, at the back, up at the top. The other connects to the front of the choke (I think it's the choke - the cylinder on the right side of the carb).

Is that second plate, and the two pipes, also part of the EGR system?

The vacuum line to the brake booster is rather odd. It comes out as a pipe. Then switches to hose. Then makes a bend toward vertical. Then there is a filter (I think) which has a 90-degree fitting on the other end. After that fitting, the line goes to the booster. It ends up with that filter stuck way up in the air. Is there any reason for this? It looks like a direct horizontal (or close to it - straight, anyway) route would be better.

I think that's all for now. If any of this sounds non-stock, or otherwise confusing, let me know and I can post some pictures.

Joe

 

[silver 80]

All stock.
you can get vacuum caps from any parts store I use napa because they are close by.
I don't know if the stock L82 will run right without the EGR. I was told that I can run without the EGR because the ZZ4 has enough over lap. Do you have the emission sticker on the hood? It will show how everything is routed.

Filter for brakes, maybe they made it that way to try and keep some of the heat off of the vacuum hose. that is stock, my 80 has it that way and the 79 L82 I had was the same.

 

[JohnZ]

The filter was added in the 70's to stop any moisture from getting to the booster and freezing it up in cold weather.

 

[MaineShark]

All stock.
you can get vacuum caps from any parts store I use napa because they are close by.

Thanks, I'll do that.

I don't know if the stock L82 will run right without the EGR. I was told that I can run without the EGR because the ZZ4 has enough over lap.

I'm not sure what will happen with the EGR. I'm definitely removing the heat riser, but I haven't totally decided about the EGR. The plan right now is to disconnect and plug the vacuum line, and see what happens. If the car runs okay, I'll take it off altogether (at least, if I end up running a non-EGR-equipped intake, which includes most performance intakes). Knowing if it would work on a stock L82 wouldn't help, either, since the engine is not original.

Do you have the emission sticker on the hood? It will show how everything is routed.

Nope. Nothing under the hood. And the small sticker on the firewall that had the emissions tuning info was pretty shredded - it fell off the last time I washed the engine bay.

Filter for brakes, maybe they made it that way to try and keep some of the heat off of the vacuum hose. that is stock, my 80 has it that way and the 79 L82 I had was the same.

Odd... Seems a pretty convoluted way to run a vacuum line. It ain't broke, so I'm leaving it alone. It's not so much the existence of the filter that I find odd... it's just the zig-zag, up-then-down routing of the vacuum line that looks very "bubba" to me.

Anyway, I'm still trying to figure out these pipes on the side that appear to be part of the EGR system. I've tried doing some searches on the Internet for detailed diagrams of the connections between the EGR and the Q-Jet, but I can't find any, so you guys are my only real hope on this.

I've got the EGR actuator, below the carb and to the rear. In a similar position, but to the front, I've got a boss with a plate bolted over it. Out of the plate come two pipes. One connects to the carb, the other to the choke (again, I think that cylinder is the choke - I'm not 100% on that). What's all that do?

Joe

 

[silver 80]

I'm looking at a dia. of an 80 in my shop man. it has the EGR valve (single nipple)
Hose from egr to upside down T one hose goes to evap canister the other one goes to a TVS from the TVS to the carb on the pass side.

 

[MaineShark]

Yeah, I've got that stuff sorted out. It's the next plate over that I'm having trouble with. It has two small pipes, and is just forward of the EGR valve.

Joe

 

[Pancho]

The other two hoses are for the choke; it pulls air from the top of the carb, heats it through a 'heat exchanger' in the manifold, and then runs into the choke body.

Totally separate from the EGR system.

Hope that helps,

 

[MaineShark]

Thanks, that makes things simple. My choke has never worked right anyway, so I'm not going to worry.

Is there a good replacement for the choke, that doesn't rely on exhaust heating? Or is the only option a manual choke?

Joe

 

[silver 80]

joe
you can go electric.

 

[MaineShark]

Hmmm... is that a major conversion? Or a simple bolt-on?

Joe

 

[silver 80]

you don't have the orig parts for your 79 do you? It came with electric choke on the carb. I don't know if you can just bolt on an electric choke or not , I've always had it on the carb. might be cheaper to go manual. I'm sure someone here must know the answer.
try looking in a jegs catalog they might have a conversion kit?
tom

 

[Pancho]

If the choke has the hot air setup, that must have been original (unless at some point someone converted it from electric !?)

What sort of problems are you having with the choke? Most of my problems were due to the choke pull-off, which was easy to fix with a new part. It takes some playing around, but mine works pretty well now. You can also check the seals and bushings inside the choke housing (in case it's not sucking a small amount of air through the pipes), those parts are in carb rebuild kits.

Does the choke housing have rivets or screws holding the cover on? If rivets, it probably means it's never been touched and so could probably stand to be gone through....

If you're still interested in converting to electric, just do a search using google or similar (I typed in "quadrajet electric choke conversion") and got lots of sites, including the following that looked pretty interesting:

http://www.carbs.net/quadrajet.asp

I don't know what kind of wiring would be involved for an electric choke, both mine (76 and 79 L-48's) are the hot air setup.

Good Luck,
Chuck

 

[MaineShark]

I'm pretty sure I have the original setup. The intake manifold is original (casting numbers come up as "1979 Corvette"), and it has the port for the heat exchanger, so I would assume that the original carb had the heat exchanger. Perhaps '80 was the first electric-choke year?

Anyway, there are two problems with the choke:
-First, it won't idle when cold. Not really a major problem - I just rest my foot on the gas pedal and keep the revs up for the first minute or so.
-Second, if I replace the intake, most performance intakes are not going to have provisions for an exhaust passage.

The choke is mounted with screws.

Joe

 

[76L82]

I think someone already answered this but the two hoses that come off a fitting that goes into the block right next to the thermostat housing, and which connects back to the EGR, is the TVS - Thermal Vacuum Switch. My manual says that it is an "integral" part of the emissions and vacuum system of the car.

I noticed that mine had literally ripped out of the metal fitting in the block and had popped out of the block altogether ...so it was pretty unlikely that this thing was doing its job....after I removed it the car ran just like it did before....hummmm...integral part of the vacuum system??

 

[MaineShark]

Um, isn't the TVS installed into a water passage in the manifold? I would think that ripping it out with nothing to plug the hole, would cause a large mess...

Joe