Hey guys. I am in the process of putting a new motor in my 81f150. It's a 300L6, with california emissions crap on it. Anyway, there is a hard steel tube that threads into the back of the passenger side of the carbuerator. I can't find out what it is from my book, so I figured I'd turn to you guys. Where is it supposed to connect? Also, where does the vaccuum line go that comes off of the egr valve? There is far too much vaccuum stuff in this truck to remember where all of it goes. Thanks in advance. I'm sure I'll have some more questions in a little bit.

 

tube in the back? Are you sure its not on the side facing the engine? Because thers a tube that threads in the side, I didn't know what it went too so I threw it out.

 

It's on the rear passenger side of the carb. I think it's the choke heat riser, but I can't find out where the hell it goes.

 

C'mon guys, nobody knows? I'd be willing to bet that one of you does....lol HELP

 

If it is a small tube that screws into the choke the it goes down to the exhaust manifold. It sucks heat up into the choke.

 

Does it actually screw/fasten to the manifold, or does it just rest down there?

 

Ha, you should see the vacuum emissions on my '88 honda!

 

I replied to the message you sent me. Please see the pic and verify we are talking about the same metel pipe. Mine is not a calif. model.

 

That heat tube goes into a recess in the ex manifold. It's not a deep hole and they are often full of rust, so drill out the rust only about an eighth of an inch. Do not drill through the metal. There is a vacuum line on the opposite side of the carb that draws air through the steel tube and through the choke coil. It just pulls heat off the manifold, (not exhaust,) and is needed to bring the choke plate fully open. There is supposed to be a woven fiberglass cover on the heat tube.

 

Just saw that recess in the ex manifold. Time for a trip to the auto store.

 

I have the exact same 1981 F-150 with california smog.

Any help you need, let me know, I know the smog stuff on this truck like the back of my hand.

Pictures are in my gallery.


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The EGR Valve:

1: The EGR valve (line originaly colored green) line goes from the EGR Valve to the black ported vacuum switch on the front.

2: There is a vacuum tee that splits off of this EGR line just before it gets to the black ported vac switch, and goes through a vacuum check valve. A small device colored light blue on one side and black on the other. From there that line goes to another tee, where it plugs into the second Vacuum controlled switch at the back. the Second one from the front, color coded red on the top. You may have to clean the very top to see the color, if it's still on it. The color codes of the switches are. Red/Red/Purple/Brown.

3: From the Second Vacuum Controlled switch, tee. The line goes through a Vacuum restrictor. A thing that looks like a vacuum line splice but is color coded to the amount of vac it sucks. (Very important don't remove). From the vacumm restrictor splice it ties into another vacuum tee and one line heads off toward the air-cleaners, White colored Thermal vacuum switch and the other line goes and connects to manifold vacuum.

4: From the top rear most port on the carberator, on the passenger side, a line goes from there to the top port of the black ported vacuum switch, originally the line was colored blue.



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You should also check the computer switches and controls on the back of the engine, to make sure they still work.

The 4 Vacuum controled switches on the back. Red/Red/Purple/Brown etc...

The Spark Retard solenoid. Located below the four vac switches

And the Tab and Tad solenoids, that are located right behind the 4 vac switches.

They can be tested using a continuity tester and a piece of vac hose.

Put the continuity tester on setting X1K and test for continuity. There may be some resistance with the solenoids but that is ok. If the solenoid refuses to show any continuity, the part is bad and must be replaced. (Junk Yard time cause the parts are obsolete)

The Color Code of the wires for the 4 vacuum switches are...

Positive side

#1 Blue
#2 Yellow
#3 Green

#1 - 3 wires are located in the "D" Connector

#4 Red. Located in the oval connector.

Their ground is black and they are ground in series, and the ground wire is also located in the Oval connector.

Check to see if the vacuum switches switch, if vacuum is applied to them. The four switches should hav continuity when no vac is applied. With Vac applied, (A hose plugged into them, while you suck on it is a good way to test) you shouldn't have continuity.

If the switches don't act like they should, replace. Again a Junk Yard item.

1981, 1982 and 1983 tab and tad, Spark Retard, canaster purge solenoid, and the 4 vac switches are compatible. The computers, carb, and other devices are not and are year specific.

Any other questions feel free to ask me.

Hope this helps.

 

no offense, but I'm sure glad I'm not in California. This is a good wealth of info here.

 

An Addendum to Number 3 in my earlier post: I forgot a component. Sorry. The addition is in Bold print...


3: From the Second Vacuum Controlled switch, tee. The line is again split off with a tee. One line goes to the wide open throttle switch located on the driver side front of the carberator. It is linkage controlled. The other line goes through a Vacuum restrictor. A thing that looks like a vacuum line splice but is color coded to the amount of vac it sucks. (Very important don't remove). From the vacumm restrictor splice it ties into another vacuum tee and one line heads off toward the air-cleaners, White colored Thermal vacuum switch and the other line goes and connects to manifold vacuum.


Sorry about that. Everything else is acurate and correct. Just double checked it.

 

Thank you so much bro! That was a definate help. I know I'm asking a lot, but is there anyway possible you could explain the entire vacuum system like you did above? When I got the truck, there were lines missing, lines broken, and just pretty much crap everywhere. I am having to start from scratch and I don't really understand the vaccuum diagram sticker on the truck. My book doesn't have my year's diagram, so I have to pretty much rely on this website to figure it out. Again, thank you for the help so far, it is MUCH appreciated. THANK YOU EVERYBODY!

 

I'll be happy to help. this might take quite a while as you know. It would probably be easier, to do this in steps.


The next step would be to hook up the vacuum advance to the distributor. I'll also try and post the meanings of the abbriviations that are on the diagram, so it will make more sence.

#1: From the lowest port on the carb, (just below the EGR port mentioned earlier) hook a vacuum line to it (original color was yellow), and from there head it off to the vacuum advance on the distributor.

#2: in this same line before it hooks to the vacuum advance, the line tees off. One line goes to the vacuum advance. The other goes to a vacuum restrictor. (Abreviation is "V-REST" on the diagram.) The vacuum restrictor is colored orange, and looks like a vacuum line splice. (very important do not remove).

#3 From the vacuum restrictor (V-REST), the line goes to the bottom port of the spark retard solenoid. The solenoid is abreviated (SOL-V) on the diagram. It should be attached to one of the valve cover bolts directly, underneath the 4 vacuum control switches Abreviated (VCS).

#4 the top spark retard solenoid port, should be open to atmosphere, with a vacuum filter (FLTR) to prevent dirt from being sucked into the solenoid.


Well, that's the vacuum advance lines explained. I'll have more tomorrow.


This is going to be like writing a book.