Another vacuum thread...304 engine

Another vacuum thread...304 engine


Active Jeeper
1979 CJ 304, 400 automatic
Trying to figure out my vacuum lines. I have the original motorcraft 2100 on my 1979 304 engine. It has the EGR, aftermarket air cleaner. It does not have the evap system or canister. Looks like the 3 port CTO is in the wrong spot? Also where do the two prongs off the thermostat housing go?....


Thanks Saddle Tramp for the download . I seen that one before. It just looks like my spark cto is in the wrong location? And from the diagram it doesn't show anything off the thermostat housing. Anyone? I need to get this cj running right.....

I run the 3 port CTO from the thermostat area, (where your 2 port (egr) is now.

Technically, they should still both work.

The diagram you show should work out good for you. You would still run everything to the right CTO's .

You can switch them around if you like (where they are) but they are actually just getting the heat from the area they are installed in, not any vac (unless I am mistaken.) They just open / switch according to temp, all the vac is supplied to and from the lines that hook in externally.

Hope this helps / makes sense.:cool:

~ JR
Ok so if I'm getting this right JR74CJ5, I hook the two ports from my thermostat housing . One to the EGR, and one to the front of the carb ported. Also my spark 3 port run it like the diagram. Correct?... I don't have the diverter valve or air pump. Just run that line on to manifold vacuum.....?
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pretty much yes exactly.

I'm not sure if you know how the CTO works and ported vs manifold vac, or why you want both to the vac advance on the distributor, but for my application, being smog exempt, i rigged this a little different.

There are tons of sites explaining in more details what each part is doing and why this goes where etc, if you want to know (id try explaining, but work is slammed today!)

The way you just described it seems like it sounds right to me though based on that diagram.

Take note of how your hoses are now, just in case I am wrong :cool:

Also, I'm still not an expert, so if others disagree, take their word for it! :D


~ JR
Hmmmmm....well I tried doing the vacuum lines by the diagram and it runs terrible . I double checked to see everything was correct. I put it back the way it was and she ran ran much better. ( distributor line on the carb, EGR blocked off and cto ports with nothing attached) By the way I do have a automatic also if that helps. I dumbfounded.....
I ran the ported vac from the carb to the "hot side" of the cto switch, and the manifold vac to the "cold side of CTO switch, then the CTO output to the vac advance on the distributor.

I also have my egr capped, as well as one of the carb ports. However this is because i broke my 2 prong CTO switch :p

Truthfully, i believe i used the port from the choke side of the carb for ported vac into CTO instead of the throttle side as shown because it was running funky, and when i checked my vac gauge it was strange... acted like a hybrid of both ported and manifold... :confused::confused:

Theory is while warming up, the manifold vac will supply additional advace since at idle it is the higher of the 2 vac's. Then when motor is warm, the cto will switch the vac to ported vac providing no advance at idle, and max at high rpm.

Manifold vac = higher vac at idle, lower with RPM increase.
Ported vac = lowest at idle, and increases with RPM increase.

With the Auto, you need a vac line to it too i believe, and from there I am lost...

Did you already get a vac gauge and check to ensure good readings and no leaks? May have a leak problem perhaps?

Hopefully another will pop up and give you some more ideas...


~ JR
...I have to pick up a vacuum gauge. Hopefully today I will pick it up...with the automatic transmission while following the vacuum diagram I used a port that wasn't being used in the intake manifold ( the one where the diverter valve is hooked up) Thanks again JR for the insight and theory on the "CTO's" I understand completely now. I will post my future results soon...

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