76 CA smog legal vacuum questions

[Brinco]

I have a 76 bronco (302 C4) that is a CA original and is in the smog program I have owned it for about 6 years and I know at some point the engine was rebuilt and I am not sure if all the vacuum lines are in place and correct although it usually passes smog. It always ran ok but not perfect. I have all the 76 shop manuals and looked on line and still could not find specifics on the vacuum system. I had a few questions that I was hoping someone had some info on. I tried to explain as best I could.......

1) The ported vacuum line from the carb has a tee in it. One line goes to the distributor (my distributor only has a location for one vacuum line) and the other goes to the bottom nipple on a temp temp valve (has coolant out the top with two nipples below.) The other nipple is connected back the EGR. Does this seem correct?

2) what exactly is supposed to be connected to the air cleaner assembly? I basically have 3 different locations that have two ports a piece for a total of six. Starting at the location where the intake(air duct assembly) enters the manifold at the bottom is the first pair. One line connects to a port in the center pair(cold weather modulator). The other line is manifold vacuum (does this seem right?)

The other port in the center pair (cold weather modulator connects to a thermal switch on the air duct assembly.

The third and final set of ports has a small port on top and a large one on the bottom. The small one on top goes to the top of the bypass valve. What should be connected to the large port?

I appreciate any info or help. I just figured a good place to start was look for vacuum leaks, and try and confirm all the vacuum lines are hooked up properly. THANKS!

 

[DirtDonk]

Tough one for anyone not intimately familiar with these. I still have to study the diagrams each time I dig into one. And you're right, they don't sound right completely. Especially the vacuum advance.

I'll see if I can come across the diagrams I used to have on the computer. One of the major auto chains (Autozone maybe?) used to have all the vacuum diagrams for most years listed on their site, but the last time I went looking for them I could not find them.
Luckily you have the books.

If we can't figure it out online, maybe sometime we can get together with the book and the hood up and do some digging? Several owners in this area that might be able to help.

For starters though, the vacuum advance was usually hooked through the temp switch, but yours sounds like it's direct but with a T to a temp switch. If that's the case, then the T isn't doing anything but potentially leaking or defaulting to full manifold vacuum after it reaches operating temp.
I'm not sure if CA Broncos in '76 had the dual-diaphragm advance/retard mechanisms like the earlier ones did, but I'm thinking they did. With yours being single only, you may end up re-routing.
I'll check my '79 when I have a chance too. It won't be the same, but some similarities would exist in the ignition vacuum system I would think. Maybe enough to make sense of it all.

Same for the air filter housing.
I'll try to snap some pics at work tomorrow (Wild Horses) on our stock '76 and the semi-stock '78's to see if anything jumps out.
Looks like leaving the old '76 stock is working out well!

Paul

 

[spap]

You might want to try checking for 1976 truck vacuum line diagram. I also believe the 76 broncos had dual vacuum ports on the dist. One actually to retard the timing to help with smog. Good luck

 

[Brinco]

Thanks for the responses I know it is difficult to explain over email. Paul pictures or sketches would be great. I have a sketch from mine and another 76 (manual) from a member on this site about 5 years ago. I have not been able to locate any diagrams for the 76 even in the ford manuals (unless i missed something).

It is my understanding that the vacuum advance should come from ported vacuum (carb). Mine comes straight off ported vacuum to the distributor. The tee I described goes to a temp switch that connects to the EGR. Is the EGR supposed to be on a temp switch with ported vacuum? I read a piece in the one of my manuals and this was how I understood it.

The other 76 (manual) that i looked at a while back had the distributor hooked to straight manifold vacuum. I tried this set up for a while but the idle rpms were very high (about 1k) and could not lower them.

Thanks again

 

[DirtDonk]

Yeah, most of our Bronco engines prefer ported vacuum over direct. But some still swear by it. I just swear at it and go with ported. ;D

Regarding the EGR, I'll let someone else who knows more get the final say, but I'm pretty sure that the valve is controlled with full manifold vacuum, but "timed" through other methods including the temperature switches.

For the distributor, naturally I forgot to bring my camera, but did get some decent shots of the '76 on my phone. PM or e-mail me your phone number (if your phone accepts pics that is) and I'll shoot a few over to you.
Basically though, the SINGLE port vacuum advance is connected via a short hose to the middle port of a 3-port temp switch on the thermostat housing. I can't remember if I noted the vacuum source though. Whether it was ported/timed or full manifold. But I'm thinking full manifold since the other port was connected to the air-cleaner heat door actuator.

The pics will help though, I'm sure. If I can convince someone at the shop to take his camera out there and join in the conversation, I will. Just gotta' catch him at the right time is all.

Let me know if you want the pics texted to you. You can call or text me at 408-398-7170 up to about 10pm pacific and I'll send them your way.

Paul

 

[Brinco]

Thanks Paul!! I will shoot you a text.