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TAC system

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TAC system
E

eatdrinkadam

Jeeper
Posts
56
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0
Location
Seal Beach, CA
Vehicle(s)
1985 Jeep CJ7 4 cyl.
Trying to figure out why I have no vacuum power to operate my tac system:

01.JPG


No vacuum power to trap door

02.JPG


Broken hose coming from Thermal Switch.. Where does this go? I cannot find a port for it.

03.JPG


Trap door hose runs to this Thermal Switch, and the broken hose runs from it.

Any thoughts on where the broken hose goes?
 
You need to fill out your profile so somebody knows what they are looking at. Every year is dif. and every engine is dif.
Basic form is vacumm to thermal sensor then to door.
 
Yup. Sorry about that..

1985 Jeep CJ7 4 cyl.

Ive looked at a few vacuum hose diagrams but still cant figure it out. Where does the actual vacuum power come from? Is it the CTO or EGR valves? Because the only external hoses that connect to the TAC system come from those valves.
 
Well it does take a "rocket scientist" to figure later CJ vacumm systems out so don't feel too bad.
I went to the Docs tab at top of page and Dyslywalker(sorry if I botched that) has provided a download for an 81 GM 151 and it shows TAC vacumm directly from manifold.
81 may or may not be same as yours but they probably did not alter the TAC vacumm source.
CTO would control EGR so it only operates when engine is up to temp.
TAC wants pure vacumm because it senses air temp inside the air cleaner house to control the door, when air temp is satisfied the TAC vents off the vacumm to allow the door to stay open.
 
Thanks for the document info.. I see that there is a 'manifold vacuum' mechanism illustrated in the diagram. I assume this is the source of the vacuum power, although I cannot find this on my Jeep PLUS the only external vacuum hoses that run from the TAC system / air supply are the ones that go to and from the EGR / CTO.

There is that one broken hose than comes from the thermal switch. (see pics) but who knows where that one goes. The hose diagrams have been no help on solving this mystery.
 
Yep, Ive read through this before.. although It wasn't much help.

I need to find the main source of the vacuum power, and then trouble shoot my way up. I have found no information on this mysterious vacuum power source.

Also, nothing Ive read gives me any leads on where my broken hose belongs. It comes FROM the thermal switch (or temperature gauge) of the air supply housing. This could be the reason for no vacuum power, depending on where it should go.

A
 
Remember that your CJ is 25 years old and things get changed, The main vacumm source is on the intake manifold right below the EGR on a AMC 258 i6 / 4.2l .
Also keep in mind when you find the right year and engine diagram that there was also a ca. version of the diagram besides the 49 state version.
If you do not have the multi hose connection shown in diagram you may have to tee into wherever you find your manifold vacumm sourse, there will be one on the bottom of the carb below the throttle plate if not the manifold.
 
Yep. I have both the Haynes and FSM documents. The FSM and misc. hose schematics did provide some clues that lead me to believe that my broken hose SHOULD lead to the manifold vacuum. None of these documents specify one WHERE that manifold vacuum outlet is (to my knowledge).

I will need to dismantle the air cleaner housing completely, and search for that darn outlet. I now know that it could be on either than manifold or carb but exactly where is still a mystery.
 
Yes that suggestion makes sense to me in theory, although I have no knowledge of "direct" vacuum power, from hoses or outlets. All the vacuum hoses I know of come from EGR, CTO or thermal valves, or other diversion sources. I would assume I would need "direct" vacuum power for this particular hose.

For all i know the complete vacuum system could be inoperable due to this severed hose.
 
eatdrinkadam said:
Yes that suggestion makes sense to me in theory, although I have no knowledge of "direct" vacuum power, from hoses or outlets. All the vacuum hoses I know of come from EGR, CTO or thermal valves, or other diversion sources. I would assume I would need "direct" vacuum power for this particular hose.

For all i know the complete vacuum system could be inoperable due to this severed hose.
Click to expand...

EGR is not a good sourse because it comes from your CTO.
The up stream side of the CTO would have straight/pure vacuum
If there is no vacuum port on your intake manifold then there will be one of usually 3 spots at the base of your carb. you have to get the right one, you should have one that feeds the CTO it would be the one to tee into.
 
Yes. I did see a few ports on the rubber housing underneath the carb. They are closed off with rubber caps. I will check those and see. If I put my finger on any of the vacuum outlets or hoses, should I feel a significant suction?
 
Problem solved.

The broken hose was indeed the hose that led from the vacuum source. I extended the broken hose and ran it into one of the vacuum ports on the bottom of the carb. (since I could not find the original source)

Trap door works fine now.

Thanks for all your help.

A
 
Sweet! :chug:
 
eatdrinkadam said:
Problem solved.

The broken hose was indeed the hose that led from the vacuum source. I extended the broken hose and ran it into one of the vacuum ports on the bottom of the carb. (since I could not find the original source)

Trap door works fine now.

Thanks for all your help.

A
Click to expand...
Great glad we all could confuse you:chug:
 
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