'76 AMC Pacer - Where does this engine hose go?

[jim1941]

'76 AMC Pacer: noticed the disconnected hose in photo laying on top of engine.  It comes out of the top of rocker cover. Looked all around and only place I can see is to plug into canister outlet at top of carburetor. Has to snake around and go under the air filter but it's a comfortable length. The shop manual calls that part with the fitting a "roll over valve and canister outlet".  It fits, but wanted to be sure where that hose goes.  Jim

[TAKerry]

Do you have an emissions decal on the core support? It may show where that goes. 

[m-mman]

It looks like you are showing two different hoses. 

 

The bigger one connected to the white "roll over valve" should lead to the evaporative emissions canister. It stores gasoline vapors until the engine is running then they are sucked in and burned. 

 

The small hose with the metal pipe will probably end up at the carburetor. The metal pipe SHOULD remain in the carb body and just the rubber hose should slip off but it is very common for the rubber to stick to the pipe and then it comes away from it's press in fit at the carb. Look for a hole in the carb body that makes sense for the length and position of the rubber hose. 

 

Tracing the small hose to its other end and identifying the function of that part will also tell you whether that part operates on manifold vacuum, carburetor vacuum or ported carburetor vacuum. Then you can look for a spot that would provide that type of vacuum. 

[Bloo]

White fitting is the bowl vent, hose is larger, fits over fitting, goes to charcoal canister. The hose below, right next to the red tag might be the one? Is it already connected to something?

 

The mystery hose has a piece of metal in it that looks like a hose connection. See if it might have fallen out of a hole in the carburetor casting. Ports on those carburetors were mostly on the throttle body, or on the back of the carburetor about halfway up. What is at the other end of the hose?

 

You need a vacuum diagram. I second @TAKerry's idea the it might be on the smog sticker under the hood. If not, it needs to come from a manual, and those diagrams are notoriously hard to find.

 

 

Edited August 12, 2023 by Bloo (see edit history)

[jim1941]

Jim again.  Think I found the right place for my hose!  Your guidance helped a lot and especially that I had it in the wrong place.  See photos. Hose comes out of top of rocker cover and you'll see where it fit.  Remember, it's a Pacer and the engine goes under the cowl and front windshield, you'll see how far back that hose originates from.  THANKS!! to all of you.  

 

Now, wondering where the hose is that goes on the white colored roll over valve; charcoal canister?  Still looking and trying to figure that one out.  

[jim1941]

Jim again,  charcoal canister is right there, easy to find.  Never thought about it before this.  Still learning about the car.  Thanks again.  

[Bloo]

"Carb bowl" goes to that white fitting. Tank goes to the gas tank vent (look for a steel vent line coming forward from the tank). "Purge" is a vacuum line, but controlled. There should be an electrical or vacuum controlled valve, most likely vacuum controlled, that turns the vacuum on to purge the canister. This happens when the car is cold and running on choke.

 

Assuming that the purge valve is vacuum controlled, there are 2 kinds of vacuum on it, purge vacuum and control vacuum. There could (probably) be a thermal vacuum valve screwed in the water jacket somewhere to control the purge valve's control vacuum. I don't recall if the control vacuum for the purge valve is ported vacuum or not. I'm thinking not. Whatever it is, it will be controlled by temperature and it will go to the smallest hose connection on the purge valve. There will be 2 large connections on the purge valve (it's just a valve). One will connect to the "purge" port on the charcoal canister. The other connects to vacuum, and a is a fairly big hose. It needs for the gas vapor that leaks in through a purge cycle to mix fairly well with the air/fuel in the manifold. It might be teed into the PCV, and it might be some dedicated port in a special place on the manifold or carburetor just for it. In most cases it will not be some random vacuum port on the manifold.

 

If you find a vacuum controlled purge valve, hook a mityvac to the small port and make sure that port holds vacuum. If it doesn't, the diaphragm is bad and you need to replace the valve. You can also check the valve part (the other 2 ports). The valve should be closed with no vacuum on the small port.

 

A typical vacuum-type purge control valve and a typical thermal vacuum valve shown below:

 

 

 

[TAKerry]

Bloo, I am getting ready to start the process of running the vacuum lines on my motor, looks like I need you on speed dial, LOL.

[Bloo]

Happy to help....

 

[TAKerry]

The guy gave my freshly built motor back without any of the lines. Said he does them after the motor is installed. I am trying to get what I can done before its installed. I know some of the stuff will have to be done after. I have the service diagrams and emissions decals etc. I will see what I come up with. Keep an eye out for a pm if I get stuck.

 

SORRY FOR THE HIJACK!

Now back to the regular scheduled program.

4 minutes ago, Bloo said:

Happy to help....

 

 

[rocketraider]

To Jim and Kerry... count yourself lucky if some yahoo mechanic didn't cut, cap or remove vacuum lines in an effort to "de-smog" the engine back when the car was new.

 

These individuals didn't understand what any of the stuff did and didn't make any effort to, but if it had a vacuum hose going to it they'd cut it. Sometimes the engine would run ok, most times they made it run worse.

 

It has always irked me when people won't make any effort to understand how something works or why it was designed that way.

 

I admit some of the emissions components didn't make much sense to me, but I knew the factory engineers were smarter than me and that carmakers weren't going to spend money developing such without a good reason. 

 

That said, I wasn't above putting a BB in a vacuum line to disable an EGR valve. Those things caused more drivability problems than any other emissions device in my experience. Used to get a lot of satisfaction out of taking one out and "cleaning" it with a 2lb hammer.