all the cars ive had, ive never seen one with some kind gate looking thing on one exhaust manifold. its got a vacuum line going to it, appears to operated by that line. not sure what its purpose is. is this part really neccessary????

 

I think its called a butterfly valve. Alot of the older cars had it, and its meant for carbureted cars.

When you start your car, its cold, so the heat from the manifold is carried up through a pipe to the opening of the air cleaner. (the old kind with the snorkel). There is also a valve in the air cleaner.

When its cold, the more heat is passed in, and less air, and when the car warms up, the heat is closed off, and the fresh air is let back in.

You dont need it.

This is a buick engine, but you get the idea.
http://cache.jalopnik.com/assets/res...07/04/455a.jpg

 

EFE valve (Early Fuel Evaporation, IIRC). I don't know if its removal would adversely affect emissions or not. Without maintenance, the butterfly is probably non-functional and as a consequence frozen open.

JamesC

 

It is an emmisions item. When the engine is cold it closes the butterfly, causing the exaust to be forced through the intake manifold crossover. The fuction is to force the engine to warm up faster.

 

Thermac system.

JamesC

 

Well, the thermac system on my LO3 uses a vacuum controled valve inside the air cleaner snorkel to divert the intake charge so that it is coming up the stove pipe.

I have never heard of another valve on the heat stove, but I guess I learn something new every day. BTW my LO3 runs fine without the Thermac. I let it warm up in the driveway every morning so that probably helps in the cold weather.

 

He is talking about the heat riser valve that goes between the left(?) manifold log and the y-pipe. Here is a picture of one from a different vehicle, could find the correct pic.

 

Yea i think im talking about a bunch of things and mixing them up. The point is, its in an e-missions thing.

One of the things in the exhaust manifold is just for heat, it doesnt circulate gas. The manifold crossover stuff is all internal (but i dont know how its activated). And theres also that valve in the air cleaner. They all work together though.

 

The important thing to check is that either it works, or that is not stuck in the closed position. If it is stuck closed it will choke the engine down.

 

yea thats what im talkin about. ive got it disconnected, and judging by the amount of carb build-up in not only the manifold, but the amount it shot out of the muffler when i first got in it, i dont think its working anyways. i disconnected the vacuum line, being i took out the snorkel for the air cleaner (going to aftermarket chromie cleaner eventually) and re-did alot of vacuum lines near the carb anyways (i hate vacum lines clogging up my vision ). not sure how to tell if its stuck open or closed, or at all, but the car seems to run fine without it being hooked up. the only thing i did notice is if i remove the air cleaner all together i get a high RPM stumble, like the motor flat lines for some reason, even happened when i inverted the air cleaner lid to get more air. but that issue went away when i put the air cleaner back on the normal way. also got a "ticking" sound comming from the carb. <shrug> but it seems to run fine despite needing plugs, wires, and a cap and rotor something terrible. they'll be comming though, just fixed an oil leak at the sending unit for press. *whew* im very impressed with the knowledge here at thirdgen :-)

 

Then it doesn't run as "fine" as it should

JamesC

 

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sorry for typos...ive got an over energetic 14 month old sittin my knee, trying to beat the keybaord up...for no apperant reason. wish i had his energy haha

 

Well yea, first of all it is not a vital part in fact on my camaro i just scrapped it entirely, (and soon i hope to get headers and get rid of the manifolds.) Second the only way it would be stuck shut is if it had been sitting for a very long time w/o being run. And even if it were stuck shut you said it was running fine? Well if it was shut the car would either blow open the valve due to pressure, or else die due to extreme backpressure. Therefore scince it is running fine the valve must either be working right or it's stuck open. The only benifit is like mentioned earlier, it helps warm up the engine faster.

 

yea its runing fine, despite the obvious tune up parts needed, and the misfire issues that come with 21 year old plugs and other ignition components. i just know i see alot of rust on the manifolds and i know the car didnt get driven much at all, i mean i got it with 50,551 miles on it haha

 

A few details to make sure everything is clear (just in case someone comes in some time in the future and takes everything that's been said as gospel).

The valve is called "EFE" for "early fuel evaporation", as stated. In days of yore, it was called the "heat riser valve", but that's a bit of a misnomer. The purpose is to force some exhaust gases through the exhaust cross over passage in the head (connected to the two center exhaust ports), through a passage under the plenum of the intake manifold, and out the other head's cross over passage and out its exhaust ports. As the name implies, it promotes fuel evaporation during early running when the engine is cold. It isn't totally an emissions thing, as it predates the SBC engine, even. Without it, your engine will be a little sluggish off-throttle before it's completely warmed up. I haven't run it since I put headers on the car in 2001. Since I drive the car year-round, it is a bit of an issue for the first several blocks on cold winter mornings. The valve is operated by a thermal vacuum switch (TVS on your vacuum decal) in the intake manifold.

"Thermovac" is typically referring to the "heat stove" system in the air cleaner snorkel. Similar to the EFE, it uses warm air to help off-idle stumble when the engine isn't fully warmed up. It also predates emissions. I keep mine operating except when I'm at the track.

Your user information says you have a 1987 with 305 "HO". The "HO" wasn't offered in 1987. If the 8th character of your VIN is an "H", that's the baseline 305, commonly called the LG4. There's a thread on the FAQ forum that discusses the differences between the 305 engines, you might find some helpful information there.

 

thats good information. it doesnt get too cold down here in charlotte, and usually if i let the car warm up for about 5 minutes before driving it, it works good. as per the HO stuff, i was going by the H vin code, plus the origonal window sticker and bill of sale. <shrug>

 

You'll be forgiven, as soon as you update your user info.

And, just for the sake of technical correctness, the gear ratio would be 2.73.

 

Hi,
Ive got an lg4 and so now I know what that thing at the manifold is...There is a metal tube the diameter of a vacuum line coming out of it , but it isnt hooked up anywhere..So, where do I connect it?
Any pics?

Hasse

 

From the FAQ forum "Vaccum Diagrams" link:

https://www.thirdgen.org/forums/atta...se-routing.jpg

 

i actually deleted mine. car runs fine without it :-) plus in deletion (complete removal), the exhaust doesnt sit as low to the ground

 

Took mine out when I installed my SLP headers. Saw the thing, and tossed it into the trash. I just plugged up the vaccum source to it and my car runs fine.

 

Did you use the 'donut' in its place that the TPI cars came with? TPI cars used the same exhaust manifolds as the 4bbl cars, but because they are EFI, they had no use for the EFE valve. Since GM used the same manifolds and Y-pipe, they just used a spacer 'donut' inplace of the EFE valve.

If you deleted the EFE valve, you should have used the donut in its place, otherwise you may end up with an exhaust leak.

 

I installed SLP headers and it didn't need it. Everything lined up perfectly. Now, the new Bosch O2 sensor, that's a piece of junk. Gonna get a walker brand.

 

i had this EFE valve on my old 84 z28, b4 i did all the work too it. i did the same thing (i.e.- toss the piecer) then again, i had a completely rebuilt block, camel hump heads, air gap manifold and an edlebrock 750, not too mention a plethora of other crap that i now miss terribly just get some headers and a y pipe n u dont have to worry bout it. also, dump the q-jet pile. they suck, specially the half-*** computer controlled ones, garbage. u can find a used 600 for like 75 bux on craigslist or something. all the emissions stuff can basically be removed on a carb car really easy. mostly cuz none of it is necessary to run the car if you just have a standard carb with no electronic hookups. be careful with the distributor though. make sure you get a non comp controlled one at a swap or online, cuz that thing sux when it gets error signals from a fiddled w/ carb engine.

 

The valve is pretty much the only thing I tossed out. Everything is still there. A.I.R. system etc...

 

lol i think i seen that on a 82 and an 85 that i put headers on ...... i was like WTF looks like a diesels exhaust brake send this directly to the scrap can

 

exactly my though when i was doing the exhaust on mine. completely worthless unless you live in alaska or north dakota.

 

UPDATE: Several months now without the gate and a Walker o2 sensor and car runs great. No error codes and no issues with the smog people.

 

they usually run better without them, as the car gets older. Everyone i've ever seen either has been stuck in one position or another. I have an all original '65 cutlass and the only "mod" is that the valve is tack-welded in the open position as it was stuck half-closed. I've seen that a lot also.

 

If I knew about that valve back when I had my Nova, I would have done what you mentioned about tack welding it.

 

kind of a long shot but I recently had this butterfly thing break on the outside of the exhaust and it was making this horrible rattling noise well at first it just seemed to make noise until o figured out what it was so I tried moving it to get it to stop and the motor seems like it’s fighting to stay running if I rev it up it’s completely fine it drives somewhat fine down the road has started a lil cutting out unless I’m on the gas I replaced plugs wires fuel filter has a new carb and it still has a really rough idle could that butterfly flap be closed and is causing my problem?

 

Probably not.

It would help diagnose your problem if we knew what your car is.

 

it’s an 87 iroc with a carbed 305 out of an 80s model c10 cars been running great for three months I have a muffler put on the car then a week later I get this ticking noise at first thought it was exhaust leak took it to the shop he fixed it but then the car would not idle at all and still had the ticking well I get it home find out the ticking is coming from that butterfly thing I moved it and it quit to me it seemed like moving it made the idle much worse I have idle set at 750 it’ll drop down below 400 then come back up and it’ll just repeat that process unless it dies but I give it a little gas and it evens out no mis fires drives fine but has a slight mis if I’m lightly on the throttle replace plugs fuel filter and it still does it

 

Sounds like it's not being opened properly. It has a little vacuum diaphragm that is supposed to open it up when the coolant temp reaches something approaching normal operating temp; like 150° or some such. It's controlled by a temp-sensitive vacuum valve that's mounted on the water outlet. (thermostat housing) That's one of 2 such devices in/near that location; the other controls the fuel tank evap system. The one for the system in question has 2 very small vacuum ports. The other has 2 much larger ports.

If it doesn't open properly it will make all the pass side cyls' exhaust try to go through the intake under the carb. The force of the exhaust from each pulse from each of those cyls trying to go through it opens it up makes it kinda flap around, which is probably what's making the noise.

It might affect the idle slightly butt it's not going to make the car die or any such thing. Anything that severe is from some other problem. Sounds possibly like a vacuum leak.

You could either try to repair the whole system, or disable it completely. Easiest way to do that is to take it off, wizz-wheel the butterfly valve off shaft and remove the shaft, and plug the holes where the shaft was with 1/8" pipe plugs.

 

The only thing that’s on the motor is that butterfly flap the rest of the smog stuff I didn’t leave on I just got the y pipe and manifolds then my buddy told me I needed that butterfly flap or I’d have an exhaust leak so I went back to the junk yard and got it put it together and it had been running fine until a week ago I done a compression test today all cylinders are at 125 to 130 fuel pressure is 6-7 psi I get no response out of my mixture screws is one thing I’ve noticed it will only kill the car when I’ve turned them both in completely other than that no response the car just keeps getting worse and worse today it was litterly idling at 200 rpm but as soon as I got the throttle it’s alive again it is not misfiring as soon as I touch the throttle it’s so weird I replaced plugs wires fuel filter pcv valve cause when I removed old one my idle improved so I thought maybe it was stuck shut put new one in same thing

 

Was there a vacuum hose connected to the EFE valve?...

 

You have to have the "valve body", so to speak, in there. Otherwise there's no way the exhaust will hook up properly. You don't necessarily need the "valve" itself for that.

I believe someone may have mentioned at some point although I'm not completely sure:

 

I removed the valve in mine and had the shaft holes welded closed. It functions as a spacer now.
I'm just wondering if a vacuum leak is causing the problem the O.P. is having...

 

probably not a vacuum leak. a worsening idle may be from plugs fouling. not likely to be caused by anything to do with the EFE, although our supposition may be based on an erroneous understanding of the system boundaries.

no telling what motor/induction system is on this 80's 305 from a C10.