I have a 1989 YJ with 4.2L block and 4.0L head. I installed (converted) from carborator to the Mopar MFI kit from Hesco.

I have the BANKS TorqueTubes� Exhaust Header for the 4.0L head.

I LOVE the header....more power... Anyway, the other night I was airing up my tires (33") while reving the engine at 2,500 rpm's and noticed the TorqueTubes "Y" collection for cylinders 4,5,6 was glowing red hot. The "Y" collection for cylinder 1,2,3 was OK.

Question: Is this normal ? or is there something wrong ?
Reason I bring this up is that I can not pass CA smog test because of high NOX (high combustion chamber temps)

Red exhaust manifolds on a dark night are common. I'd bet if you run her a while and quickly raise the hood both would be red.
Exhaust heat can be helped by increasing the timing. Does the computer you installed control the dist?
If not then I'd be retiming the engine. If it DOES control the timing as well as the mixture there is little you can do.
In short most exhaust manifolds on most vehicles are red at all times on the hiway... one just doesn't get to look at them.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

I have seen this caused by the incorrect or improperly gapped spark plugs, which caused the air fuel mixture to finish burning in the exhaust. As Jim mentioned, retarded ignition timing can have the same effect.

High NOx is cause by high combustion temperatures. High combustion temperatures can be caused by a hand full of different scenarios, both mechanical and electrical.

The leading mechanical cause of high NOx is high compression ratio. A high compression ratio takes a (relativly) large amount of air/fuel and compresses and heats it. When the mixture is lit, it burns hotter and faster then a low compression engine. The common solution to this is an EGR. The EGR puts some of the exhaust gas back into the combustion chamber. This, of course, does not physically decrease the compression pressure or temperature, but it does lower the burn temperature buy substituting fuel for an inert gas. The 4.2 comes stock with an EGR. The 4.2 has a C/R of 9.2:1 where the 4.0 has a C/R of 8.8:1, I'm not sure but swapping heads may raise the C/R even higher.

Timing advance is the leading cause of high NOx in the electrical system. The whole point of having advanced ignition timing is get as much of the fuel burnt as reasonably possible to apply the maximum amount of pressure when the piston hits top dead center. It takes roughly 3 millisecond (0.003s) for the fuel to burn from the spark plug to the other side of the combustion chamber. While the fuel is burning, the engine is still turning. if you lite the fuel before TDC, the engine will still be compressing the fuel while it is burning. So not only is the pressure and temperature increasing because the volume is decreasing, but increasing because the fuel is burning. This is perfectly fine for the most part. The piston is near the top of its stroke and has a lot of mechanical advantage over the high pressure on the piston. What this means for the fuel is a high temperature burn, which increases the overall pressure pushing down on the piston.
The net effect is more HP out, but high NOx due to the high temperatures. More applicably to a hot header, ADVANCED timing will lower the exhaust temperature because the fuel is all burnt and a lot of heat and energy was extracted from the power stroke of the engine (increased volume, decreased pressure and temp). Unfortunately there is a limit. If you advance the timing too far, the increasing pressure and temp from the fuel burning combine with the pistons up travel will hit a limit and cause the remaining fuel to spontaneously ignite. You hear this in the form of knocking.
Retarding the timing will cause the spark to go off at or after TDC. Now the piston is on it's downward travel as the fuel burns. The volume is decreasing as the piston moves down lowering temp and press, but the fuel is burning increasing temp and press. There is still plenty of heat and pressure built up from the fuel, but the fuel does not burn as hot as the advanced timing scenario. This will lower the NOx, but will also lower the HP out. Consequently, the header will also be hotter. If the timing is very retarded, there is a good chance the fuel will still be burning in the header.

Unfortunatly, there is no easy solution to your problem, and of the solutions you're going to loose HP.

1. Retard the timing. This probably won't even work. If you are running the 4.0 injection and computer, the timing is controlled by the computer. Even if you rotate the distributor, the computer will compensate until it goes hay wire. If you are running a different EFI, you may be able to retard the timing. This will fix your high NOx, but increase the heat on your header.

2. Install an EGR. This again will fix your high NOx, while not effecting the heat on your header, or slightly lower it. Unfortunately, for CA smog you are not allowed to change the smog control devices on the motor. You could go to a smog ref and explain the whole swap, (you might have already) and get ok'ed for an EGR, but... installing one that works right might be the end of your header.

3. Install a spacer Head gasket to lower the compression. This will fix the NOx issue, but lower HP. It may also stop the header glow. This is a viable option for smog, and all you need to do is change out your stock head gasket for a thicker head gasket. Most machine shops have them available for making up the missing metal from decked blocks and heads.

4. Remove the header. A good header will allow more of the exhaust to leave the combustion chamber then a stock exhaust manifold. Sometimes the left over exhaust acts as a EGR if enough is there. By putting a header on the motor and scavenging more exhaust the combustion temps may have increased.

If it was failing NOx before the header, I'd probably install the spacer head gasket. It should fix the high NOx while leaving the other engine parameters alone, leaving the nice simple EFI system.

If it is failing NOx after the header... pull the header to pass smog.

As for the header glow, I wouldn't worry about it. Headers are usually thinner than the stock manifold. The thinner metal does not resist heat flow as much and tends to run hotter on the outside surface.

Lately, the most common failure cause for high NOX, if everything checks out normally, is the aftermarket Cat-Converters. I'm especially refering to the small units that used to cost around $100 -$150 installed. These small units skimped on the Rhodium element that catalyzes the NOX and rarely will make it past the second smog test. The state of CA requires a new, "CARB EO" certifed converter to be installed now that the manufacturers have to warranty for 5 years. While working at the Jeep dealer, I used to see alot of '91-'95 4.0l Jeeps that failed the NOX by 100-200 PPM then pass when a new factory replacement cat was put on with only 100-200 PPM NOX total (Usually around 600 ppm NOX is the limit).

MartySoCal,
I read this on the internet couple weeks ago. I replaced the CAT the other day and will go get smog test this week. Will let you know the outcome. BTW - the new CARB EO cat was $253.00 install. Compare to $149.00 installed 2 years ago. I looked at my 2007 smog test results and NOX was on the upper limits.

I've seen a lot of people buy an expensive cat to pass smog, then fail again 2 years later.
The underlying condition is high NOx. A cat will scrub close to legal limits for a while, but it will burn it up in time.

The problem is that the cat's they were buying were probably not made to factory quality specs, that's why the state of California changed the requirements. The so called "High-Flow" replacements were the worst as they usually had even less catalyzing material in them (Rhodium, Platinum and Palladium, all very expensive metals). Two years of use were usually enough to cause enough wear and erosion to prevent them working properly.

Here's some links on this subject:
http://www.arb.ca.gov/msprog/aftermktcat/amcatq&a.pdf

http://www.bar.ca.gov/80_BARResources/ftp/pdfdocs/ARSC-summer08.pdf

http://www.arb.ca.gov/msprog/aftermktcat/aftermktcat.htm

The notes from the hearings in the last link are interesting.

Hope this adds to the discussion!

When I was at JC we would do CAT efficiency tests with two five-gas analyzers to learn basic diagnostic skills. My jeep at idle and 2500 (no load) put out low enough emissions to pass smog, before the CAT. After the cat the readings were even lower. Heck even on the dyno in 3rd gear WOT ~2800 RPM the jeep was only putting out 61 ppm HC and .05 CO don't remember NOx.

What I'm saying is an engine with a good tune on it should pass smog with a bad CAT. The cat is there to take those good emissions and eradicate them as much as possible. If you are running way out side spec the cat will burn off as much excess as possible. Unfortunately, this raises the temp in the CAT. Even if it doesn't burn it up quickly, the CAT will be outside its nominal operating temp and will burn out eventually.

You can always throw a CAT at it and pass smog if you are border line over. But if the condition is severe enough, you might burn out an expensive cat in 2 years.