Cylinder 3 header tube glowing orange at idle

[neverdone]

Hello everyone. 
 

I’ve got a really odd issue I’m working on. I recently bought new headers from Ireland engineering, the tri-y race headers with a ceramic coat. Upon installing them I noticed a small hole at the bend point in cylinder #4’s primary. I was annoyed but welded it up and continued on. I promise this is relevant later. 
 

I fired the car up and let it idle and noticed the primary on cylinder 3 was glowing orange?! I shut the car off and it backfired out the exhaust. Previous to this my car was running fine, no backfire, and no glowing headed tube to my knowledge. I have an AFR gauge installed in the 02 sensor hole and it’s reading just fine throughout all RPM’s. 
 

Are these headers seriously this thin or do I have a major issue in cylinder 3? My timing is fine, checked and double checked. If it was off I would expect all header tubes to glow not just one. Carbs are synced properly, all pull around 5 on the synchro meter. Cylinder 3 pulls a hair higher than the rest but this can’t be a major issue. I checked everywhere for a vacuum leak with propane and carb cleaner and can’t find one. 
 

I pulled my plugs and cylinder 3’s is lighter than the rest by not by a dramatic margin. 
 

I removed my chokes, aux Venturis, and jet stacks to verify all parts are matching and in working order. I tried retuning the carbs but landed back in pretty much the same spot adjustment wise with the AFR in the same zone of 12 at wot to 13ish at idle. 
 

what could be causing cylinder 3 to be running so much hotter than the rest? Is this set of headers just junk and too thin? The car runs completely fine with the exception to the backfire on shut down which I am assuming is fuel detonation in the crazy hot header’s. 
 

here is my carb set up if it’s relevant at all. Dual Weber 40’s 

F8 55 idle jets 

32 chokes 

F16 emulsion tube

160 air

135 mains 

40 pump jets 

4.5 aux Venturi 

[2002iii]

Looks like a Chinese ePay header!!!

[TobyB]

Bright red is 1600f or more, so it's a carb issue somehow.  Idle EGTs should be in the 

'bottom of the gauge' department, so 1kf or less.

 

Not to say the header's all that fantastic, but even aluminum foil ought to work at idle.

 

An air leak in the exhaust system will certainly cause backfiring.

 

fwiw,

t

 

[jimk]

Normal exhaust gas temperature at idle is around 650F.  Shouldn't see any heat color at that temperature.

[edgefinder]

I watched my girlfriend go down the driveway, turn onto the road, house blocked my view for a moment then car reappeared and the cat converter was glowing red. I yelled and she came back. 90's Mustang with v6. Hell I don't know but I had the injectors out that nite and took them to a shop next day. They were all good so took car to the dealer next morning and said put it on a scope and see if they all get signal correctly, don't go over $100 on work. They called later and said they checked everything next step is pull injectors. I went back and showed the service manager the injector shop receipt, the mechanic said he didn't tell me that. I went to the parts counter and got a repaired PCM that had been discussed. Apparently it failed holding an injector open. Problem fixed. I think one of your carbs is dumping extra fuel and its burning in the exhaust 

[visionaut]

Possible large restriction somewhere within tube 3?? 

[neverdone]

1 hour ago, edgefinder said:

I watched my girlfriend go down the driveway, turn onto the road, house blocked my view for a moment then car reappeared and the cat converter was glowing red. I yelled and she came back. 90's Mustang with v6. Hell I don't know but I had the injectors out that nite and took them to a shop next day. They were all good so took car to the dealer next morning and said put it on a scope and see if they all get signal correctly, don't go over $100 on work. They called later and said they checked everything next step is pull injectors. I went back and showed the service manager the injector shop receipt, the mechanic said he didn't tell me that. I went to the parts counter and got a repaired PCM that had been discussed. Apparently it failed holding an injector open. Problem fixed. I think one of your carbs is dumping extra fuel and its burning in the exhaust 

I would buy either a hyper lean or very rich scenario but my AFR gauge is showing right on the money? Is it possible my reading is just drowned out by 3 proper cylinders and one with an issue? 

[Dudeland]

Maybe your cam skipped a gear, and your exhaust is opening too soon. It shouldn't be that hot. That is like a 2 bar turbo at 6K rpm hot; if you are not careful, you will melt the valves. 

 

The fuel may completely burn in the header; therefore, the mixture is on point when it hits the AFR.  

[Dudeland]

I have the exact same header with the ceramic coating. Mine does not glow.  Stop running it until you get some answers. 

[John76]

12 hours ago, neverdone said:

what could be causing cylinder 3 to be running so much hotter than the rest?

Just a few thoughts ...

Are these steel or stainless? Are they coated with ceramic or chrome?

Is the #3 gasket installed properly? The metal surface should face the header with the soft surface facing the head.

Also, #3 header tube is surrounded on all sides by #1, #2 and #4, so might explain the "glow".

As @TobyB pointed out above, steel will start to glow a dull red at 1200 F, and cherry red at 1600 F.

You typically would not see any color at these temperatures if the surface was shiny (stainless, chrome, etc.).

[John76]

12 minutes ago, Dudeland said:

if you are not careful, you will melt the valves. 

Among other important things!

Aluminum melts at 1200F and does not even glow red before it puddles.

[Preyupy]

You said that the #3 cylinder is running more air (based on the carburetor balance)  this on top of a difference in idle mixture screw settings between the 4 cylinders could be causing this.  There is also the possibility that the ignition timing on that single cylinder is off ( I have seen Pertronix magnets that have been improperly placed in the plastic ring)  It would be a good thing to put a TDC mark for cylinders #2&3 and check them just in case. 

 

If the air flow is different between the 2 throats of the same carburetor the throttle shaft has been twisted and the only way to balance them is to "re-twist" the shaft back.  This usually happens when people install the linkage arms and tighten the nuts relying on the stop at the other end of the shaft to keep the shaft from "twisting". 

 

Remember your O2 sensor is looking at an AVERAGE of all 4 cylinders,  You could easily have one really rich cylinder and one very lean cylinder and it might average out to a very acceptable number.   

 

 

 

 

 

[Dudeland]

57 minutes ago, John76 said:

Just a few thoughts ...

Are these steel or stainless? Are they coated with ceramic or chrome?

Steel tubes with ceramic coating. 

[visionaut]

Are the tubes equal length? If not it’s like a different tune per cylinder.

 

In a Tri-Y, for pulse timing, cyl 3 is paired with 2, and 1 with 4.  So as each exhaust pulse passes it pulls along the charge arriving from the other cylinder. So 3 getting hot has possible effects from cyl 2 as well…

 

And before you go deepdiving into carbs and timing, given the great manufacturing QC, please try running a long coathanger through each tube (primaries & secondaries, particularly the 2-3 collector… Restricted tubes get locally hot. 

 

 

[Son of Marty]

2 hours ago, John76 said:

Is the #3 gasket installed properly? The metal surface should face the header with the soft surface facing the head.

He's using the later one piece gasket, don't see how it would fit any other way.