Chad, this may help:

Illustration Section 94.1, page 32 / 1978/ F100 351M/400, Emission System, EGR.

This will essentially be the same for all 1977/79 F100/350's with 351M/400's.

The vacuum lines and all the smog junk (except the smog pump stuff) on the engine is shown in this pic.

 

Thanks, Bill!



Looks like it's a great reference (if this diagram hasn't changed since this one) to use for future references. 351M/400 questions are as plentiful as split brass fuel floats. I'm going to compare with my '78, too.

 

You don't have to change the coil, but I like to on my trucks. I've always noticed an improvement after changing it. Most coils I've replaced are the ones installed from the assembly line!

Ah, so that explains your thread about setting the idle on the carburetor. Yes, I'd suggest you rebuild it and solve the vacuum issues.

 

Thank you very much for your assistance by scanning and posting these parts catalog pics.

 

Welcome. Always glad to assist.

 

Try this site

 

Well, after inspecting closely I discovered several things.

1) When I pumped the throttle fuel came out of the carb base gasket. Bought new carb & EGR gaskets
2) When I sprayed cleaner around different places, I found RPM rises when I sprayed: The shaft of the carb (about 30-40 RPM rise), but the biggest rise was when I sprayed in between the distributor cap and the vacuum switch for the advance (about 100 rpm rise).

So, I pulled the carb & EGR spacer and found that when it had been put back on last time it had not been fully torqued and they did not use an EGR spacer gasket but instead used a solid carb gasket with no holes for the exhaust. This blocked the port and it was clogged with soot and the corner of that port on the manifold had begun to be eaten away by the exhaust pressure. I cleaned the whole thing up and got the carbon off of the carb mounting surface, out of the hole and prepped it to go back together. I doused the carb with cleaner, replaced the gaskets and torqued to spec. The EGR vacuum hose was blocked (and still is because I don't know where to hook it up. Anyone know what the vacuum source for the EGR should be?

I got it all hooked back up and ran it. It runs better but I still wound up with the throttle plates fully closed and the idle mixture screws turned out 4 turns to idle well. Its obvious to me that I should rebuild the carb or replace it but I'm wondering about the intake leak indicated by spraying in between the distributor and vacuum switch. Does anyone know why I would get an RPM rise here or how to seal it? Maybe the advance vacuum switch is leaking where it connects to the distributor?

Thanks,

Scott

 

When you replaced the upper/lower combo EGR plate and carb spacer plate gaskets, did you notice the condition of that plate?

From the factory, the spacer plate is aluminum. It's notorious for burning out and melting!

The over the parts counter Ford replacement plate is cast iron.

The gasket used between the carb & spacer is MUCH thicker than the gasket used between the spacer & intake manifold.

 

The inside of the plate was covered with carbon and pitted from the exhaust pressure and the thickness of the wall was about 1/2 of original on the side that feeds the EGR. I did get the correct gaskets - the gasket for the carb to spacer was about 1/8" thick with built in washers with up/forward markings and the gasket for the spacer plate to intake manifold was quite thin with two holes to match the EGR.

I feel sure I'll have all this off again before long and will probably replace the EGR spacer plate with the steel version.

Do you know what the correct place to hook up the vacuum source for the EGR is? If that thing is operating properly it seems like it should lengthen the life of these components.

Scott

 

The EGR routing varies. It depends on its DSO, whether it has an emissions control package or not, and if it's a Federal or California vehicle.