Capt_Wolfman Posted December 27, 2019 Report Share Posted December 27, 2019 Hello! Just bought a 78 620 and I’m new to the forums. I recently tried to get emissions tested and it failed via the air system check. The guys at the emissions testing facility pointed out two nipples on the bottom of the CAC valve that were not connected to anything. So my question is what are those and where do they connect? I’ve tried looking around but only saw info on the main air lines to the valve. Added a pic to help identify. https://imgur.com/tmN2yEc Quote Link to comment
datzenmike Posted December 27, 2019 Report Share Posted December 27, 2019 The CAC (combined air control) adjusts the air from the pump to more accurately control the catalytic converter temperature. My diagram shows both small pipes join together and then connect to the intake manifold. Inside the rubber hose is a small orifice or reducer to regulate the vacuum signal. I found an 'air hose to CAC valve' 18716-B9900 dealer number. (very unlikely they will still stock this part) Any proper size hose will do. You'll need a Y so that it connects to both nipples on the CAC. Can you send a picture of the front intake runner. My diagram shows the hose connecting to it and if missing it must have been plugged. Perhaps it is disconnected from the CAC and you can find it and put it back.. Hope this helps Quote Link to comment
Capt_Wolfman Posted December 27, 2019 Author Report Share Posted December 27, 2019 49 minutes ago, datzenmike said: The CAC (combined air control) adjusts the air from the pump to more accurately control the catalytic converter temperature. My diagram shows both small pipes join together and then connect to the intake manifold. Inside the rubber hose is a small orifice or reducer to regulate the vacuum signal. I found an 'air hose to CAC valve' 18716-B9900 dealer number. (very unlikely they will still stock this part) Any proper size hose will do. You'll need a Y so that it connects to both nipples on the CAC. Can you send a picture of the front intake runner. My diagram shows the hose connecting to it and if missing it must have been plugged. Perhaps it is disconnected from the CAC and you can find it and put it back.. Hope this helps What exactly is a front intake runner? Not familiar with that term and want to get the pic you your asking for. Quote Link to comment
datzenmike Posted December 27, 2019 Report Share Posted December 27, 2019 See the rubber hose coming out of the intake and looping into a rusty metal line? Just below it on the intake is a rusty plug. This is where the CAC hose should connect for it's vacuum signal. Quote Link to comment
Capt_Wolfman Posted December 27, 2019 Author Report Share Posted December 27, 2019 Found it. Thank you https://imgur.com/a/Aj5ny35 But the two lines coming off of it are connect to CAC valve and the fuel shut off vacuum switch. https://imgur.com/a/msBScS1 Found this diagram and in the bottom right corner is the CAC. The hose looks like it is just routed into it self. Could that be correct? https://imgur.com/a/XTmZt2x Quote Link to comment
datzenmike Posted December 27, 2019 Report Share Posted December 27, 2019 There should be two hoses on the manifold, below. One from the CAC and one from the fuel shutoff control go to the intake below. Not sure what the red circle on the right is. Maybe a T fitting should be there with a hose down to the second nipple on the CAC? This doesn't show the two hoses to the intake. Quote Link to comment
Capt_Wolfman Posted December 27, 2019 Author Report Share Posted December 27, 2019 Yes, that is correct. There are to hose connection on the manifold fitting. The circle on the right is the connection from the manifold fitting to the fuel shutoff control. There isnt a T there. I think someone just put a fitting there to extend the hose length instead of getting a correct length hose. In the shop manual I got with the truck it shows those connections but nothing about the two connections on the bottom of the CAC. https://imgur.com/a/XrMuQAC https://imgur.com/a/COgb594 Quote Link to comment
datzenmike Posted December 27, 2019 Report Share Posted December 27, 2019 True it only shows one hose but your picture shows 2 nipples... The '78 620 FSM, top right of page EC 8, shows the CAC valve with 2 nipples with hoses that join into one and then connected to the intake Quote Link to comment
Capt_Wolfman Posted December 27, 2019 Author Report Share Posted December 27, 2019 I looked up the 78 620 FSM you mentioned and see what your talking about. So I'll just grab a Y contention for the two nipples then T it into the line going into the intake manifold? Sorry for the confusion on my part. I appreciate the help. Quote Link to comment
datzenmike Posted December 27, 2019 Report Share Posted December 27, 2019 It's no problem at all. We'll get it figured out. Quote Link to comment
Capt_Wolfman Posted December 28, 2019 Author Report Share Posted December 28, 2019 Just got back from emission and it passed! Thanks again for the help. Quote Link to comment
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