Glowing downpipe

[lorkp]

Hi all, my car is a California '79 320i, and so has the thermal reactor until death does it part ... out. The car sat a long time, but after going through the fuel system I was able to get it started.

While I get that the whole point of the reactor is to get super hot, I'm concerned something is not right because just during the course of trying to time the car, maybe a few minutes at 2200 RPM, the down pipe is getting red hot, and the reactor starts to smoke. Before firing the car up I adjusted the valves, and in a leak down test I didn't hear any air coming out of the exhaust. And I don't think it's too lean? I don't have a CO meter, but have the mixture adjusted per the FAQ. What should I take a look at? Thank you for your help!

[Rushfan1]

Perhaps totally non related but I once had a glowing down pipe/catalytic converter and a rough running engine. This occurred because my spark plug cables were accidentally switched between 3 and 4. Something to check just in case you recently replaced your spark plugs or spark plug cables.

[320iAman]

Check for blockage in the exhaust system down stream, a replacement of weaker thinner metal and too lean Air/fuel mixture are causes, another cause if your running a turbo is pushing too much exhaust thru too little of space.

When you find a solution ,, share it..

Randy

[Yonkers320is]

Put a wideband afr meter on the downpipe, check it might be too lean.

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[ascot]

You mentioned checking the timing.......................Did you rotate the distributor? Sounds like you turned the distributor too far and it is causing it to run too hot in terms of combustion temps. Get a timing light on it and fire it up and check the timing as soon as you get it fired up. Also, I would not think the mixture is too lean but rather too rich! Remember the thermal reactor works somewhat like a catalytic converter and when it encounters too much fuel it gets extremely hot! Many 530i owners replaced their thermal reactor manifolds with the European manifolds as the high heat when the mixture got too rich often resulted in warped or worse, a cracked head.
shermanmartinez at hotmail dot com

[lorkp]

Thanks for your comments guys. It looks like the car was running crazy rich. Attached is a photo of a new-ish plug I just took out—this happened after only running the car in my garage for a couple days. (BTW I think there's some oil fouling happening too). What set me down the wrong path was that when I originally got it running, it was surging and richening the mixture caused it to steady, so I figured I was lean. Although I couldn't keep the engine running without throttle—which in hindsight was a clue—but I figured I had a vacuum leak or something. And then the conventional wisdom being that lean cars run hot ... So I was completely turned around. I backed off the mixture screw a turn or so, and now it's actually running quite nicely and needs no throttle to keep going.

Ascot—your comment about the reactor working overtime due to a rich mixture makes a lot of sense. And I wonder if basically the mixture was so rich that the combustion was continuing outside of the engine. Unfortunately I can't take the reactor off due to California regulations! Wish I could install a different manifold and cat.

Yonkers—I would like to set the mixture objectively using a wideband, or the Gunson Gastester that's talked about on Pelican, and it's an investment I'm weighing. I think if I could get something for under $100 I'd take the dive. I've set eBay and CL alerts. I'm thinking about sticking a cheap narrowband O2 in my tailpipe and reading the voltage, to get a primitive idea as to whether I'm in the ballpark, but perhaps it wouldn't get hot enough to work.

[320iAman]

"The thermal reactor is a exhaust manifold made of stainless steel rather than cast iron. The purpose of the thermal reactor is to better allow the burning of exhaust gases by air injection. This was an early form of catalytic converter."

So too much fuel caused too much heat and turned the down-pipe cherry red.

The 02 sensor on 80-83's is in the exhaust manifold is close too the down pipes ,the O2 sensor gets hot fairly quickly if your thinking of placement of the bung.

Randy