Glowing Red Catalyst

[PursuitSpecial]

I got home tonight and opened my hood to check on the engine and the entire engine bay was bathed in glowing red light from the pre-catalyst thing under the exhaust manifold. The actual catalytic converter itself has been removed but I left the pre-cat or whatever it is in place. For some reason it's getting insanely hot, I don't think it's stopped up because the car doesn't drive any different than normal and has the power you'd expect from a slant 6. The car doesn't act stupidly rich or anything, but this could be indicative of the fuel mileage problem I've been having. Now, recently, I've also had problems with the carburetor freezing up in cold wet weather, so I hooked the breather up to the manifold and put straight vacuum to the air cleaner valve so it's always intaking air straight off the exhaust manifold. It solved the icing problem, but is there any way it could cause the engine to put tons of unburned fuel in the exhaust? Maybe if there's an exhaust leak in the manifold it's sucking in exhaust gas instead of oxygen and going rich and not burning all the fuel? I don't want to drive the car until I get this solved, the cat was so hot it could easily start a fire.

 

[AMC Diplomat]

hooked the breather up to the manifold and put straight vacuum to the air cleaner valve so it's always intaking air straight off the exhaust manifold.

Huh? So your always pulling hot hot air into your carb and throwing off the fuel/air mix? I don't know what temp a slant 6 gets to but the manifolds on my 318 can go to 500 degrees.

Anyways, my first thought is you have a heat riser problem. These links can explain it better than I can heat riser question - Slant Six Forum
Manifold temperature - Slant Six Forum
exhaust manifold heat riser - Slant Six Forum
Second thought is you don't have the little pre heater hose hooked up like in this pic

See that tube below the front of the air cleaner snout? That pulls hot air off the manifold to the air cleaner.

What's interesting is you're getting icing in North Carolina on a reverse flow engine. Are you using ethanol gas? Ethanol gas can cause icing at higher temperatures than real gas

 

[PursuitSpecial]

Yeah, that's the same setup I have. I just put it back together like that where it had been taken apart. The heat riser spring broke which is why the carb freezes so easily. Anyway that's not what's causing the problem, I unhooked the pipe and it's still glowing. I then unhooked the air pump which gives fresh air to the cat and it stopped glowing, now it smells extremely rich, it was hiding the problem. So I think I need to rebuild the carburetor and put in a new float in it or something, it's running very rich so the catalyst gets red hot but not rich enough to cause any kind of driveability problem, it runs perfect, could be where my mileage went also.

 

[AMC Diplomat]

Yeah something else has been messed with

 

[Aspen500]

The air injection system should only direct air to the pre-cat during engine warm up (unsure what temp the threshold is, maybe 160?). Anyway, it then switches to downstream. If air is constantly injected to the pre-cat, it WILL glow red. Think blacksmith blowing air into a coal forge to increase the heat.

Take a look at the plugs after a drive and read the insulators. Compare to a chart. If they look good, it's not running that rich. Keep in mind, without a cat the exhaust will smell rich. You said the rear cat is gone, and the pre-cat is most likely depleted and not doing it's job like it did 30 years ago.

Not saying there isn't something wrong with the carb or ignition, just some other things to consider.

 

[AMC Diplomat]

I second Aspen500, no cat + no smog pump = smells like the 80s. I wouldn't call it a rich smell. I think it's more like how everything used to smell on a cold morning downtown in traffic. Minus the cigarettes.

 

[Mikes5thAve]

With no main cat or no cats at all it still shouldn't smell that bad.
Leave the air pump disconnected and check what the plugs say. Could be anything going on with a 40+ year old car.

 

[GregG48213]

catalyst gets red hot

I had a similar problem on my '88 Diplomat (with a 318 & Quadrajet): main cat glowing bright red, air pump long since disconnected. It turned out the choke had failed (again) and it was running stinking rich (not opening all the way). Rochester used an electric element on this Q-jet and I had replaced it when I first got the car at about ninety thousand miles.

 

[PursuitSpecial]

I rebuilt the carburetor for the first time since it left the factory and found some very interesting things. The power valve that screws into well of the bowl had backed completely out of the hole and was laying over off the plunger, so I made a custom slotted screwdriver to go around the rod and tighten it back into place. Also the nitrophyl float felt soggy with gas and it lost about half a gram letting it sit overnight, so I replaced it with a new brass one. Other than that, the carburetor was perfect inside. The car runs noticeably better now, the engine sounds smoother, no more rich smell, and the catalyst isn't glowing anymore. I think the main culprit was the power valve, with nothing plugging that hole the carb was sending a bunch of extra fuel down the intake and a heavy float would just make it worse. It's a wonder how the engine was running so good when it was that rich. I bet my fuel mileage is gonna pick back up now too.

 

[Kern Dog]

I glowing converter would indicate a lean mixture in my opinion but hey.....I'm curious to see what happens with the air/fuel ratio back where it should be.