Glowing Exhaust Manifolds

[Kaweh]

Hello, I've read a lot of posts here over the past 4 months and so I thought I'd chime in for some possible RVer insight. I drive a 34' Winnebago Elante year 1992 with a 7.4L Chevy. Five months ago I had a backfire that was caused by the injector wire grounding out to the throttle body. Ever since that was fixed I've noticed the exhaust manifolds glow under a load. Lots of testing led me to learn that the manifold vacuum was not steady and so I even went as far as rebuilding the engine. I left the camshaft alone but changed the lifters even though they were fine. The previous exhaust manifolds were cracked so I put on new ones and the heads were sent to the machine shop and came back looking brand new. Other things that were changed are the MAP sensor, O2 sensor, engine coolant sensor, water pump, timing chain, of course a full tune up and initially we thought the catalytic converter was clogged, which it wasn't so i put a new one in and checked the muffler too. So now it's rebuilt with a new computer, the right injectors and a new higher performance fuel pump.

The fuel pressure now reads 12 psi. All cylinders were tested and show 150 psi, the fuel pressure regulator was rebuilt as well, The car fires right up and has great power in the city or straight a ways. The timing is advanced 12 degrees and I've ran it at 4 whites factory spec and at 6 degrees advanced and no matter what I've tried and tested it still makes the exhaust manifolds glow ridiculously red when i'm going up a hill. Giving it more gas just makes them glow more. So bad that at night you can see the both manifolds glow all the way past the Y pipe. Its scary!!!

I've replaced all vacuum lines, tested for vacuum leaks (none found). Its bizarre, I've met some amazing mechanics over this past 6 months and they are all stomped!

So i read a lot on here about how some folks put on headers and I know that this year 454 was prone to exhaust leaks, restrictions and manifold cracks. So I wonder did ya'll have this happen to you too or do you think it's normal for the manifolds to glow like crazy when on a hill? Is it somewhat normal for them to glow? If so to what degree? Cause this is scary bright red and even though i've had people say it's normal.... you're putting a lot of strain on this engine and 16,000 pounds blah blah blah, I don't buy it and here is why....... Some wise guy who owned it before me had put on air horns. Well the compressor for the horns was all the way in the back of the coach and the holding tank in the front by the radiator! Dumb design! nonetheless, i have owned this RV for six years and we went to Burning Man in it all six years and before this happened my air horn worked. It turns out when the manifolds started to glow, it cracked and melted the air line. the line was going along the frame and past the right exhaust manifold. And so if they were glowing before like this, the air horn air line would have bursted before. So that's how I know this is not normal.

Any thoughts are appreciated. I'm considering changing the exhaust to duels and a chip upgrade from tbichips.com but the car has been fine since 1992 and I don't think i should have to upgrade stuff to stop it from burning up the exhaust manifolds.

Ok, thats it for meow. Thanks for reading!

Kaweh
www.kaweh.com
Spanish Guitarist San Francisco Bay Area.

[Wes_Tausend]

...

Make sure fuel pressure remains up on hard pulls.

One other thing to check. Make sure that the gasoline that's used is not premium. Higher octane fuel burns slower to prevent detonation in high compression engines. But in the lower compression engines, especially those used in severe truck service, the high octane is detrimental and causes higher exhaust gas temps because it is still burning during, or shortly before, the exhaust stroke.

Some folks, even mechanics, think they are giving their engine a treat by using high octane. They just don't know how engines work and follow the usual old wives tales without thinking it through. The worst thing one might do is use aviation fuel that has such a high octane that it will damage ordinary automotive engines in short order. Premium pump gas can cause a similar function to a lesser degree. High compression aircraft engines are made to run at low rpm which affords plenty of time for a long complete burn, as opposed to automotive engines that often cycle at higher rpm and require a quick burn.

Wes
...

[othertonka]

moisheh wrote:
Something is wrong if you are running 120 on the flats. Do you have a thermostat installed. No modern engine should ever run at that temp. ?????? It should be running @ 190 at least. What are you using for a Temp gauge?

Moisheh

I noticed the same thing, 120 degrees on a flat road? something is wrong with that. Check the gauge and the thermostat.

[moisheh]

Something is wrong if you are running 120 on the flats. Do you have a thermostat installed. No modern engine should ever run at that temp. ?????? It should be running @ 190 at least. What are you using for a Temp gauge?

Moisheh

[JimFromJersey]

I'm not a metallurgist, nor do I play one on TV. But I swear I once read somewhere authoritative that with regards to components made of cast iron, if they "overheat" once, and reach a higher than normal temp, (e.g., "the sum***** GLOWED...") the tolerance of the iron is reduced somewhat, and they "overheat" easier from then on. In other words, the 1500 degrees that was needed to burn them the first time, has now reduced to 1200 or even 1000 degrees. Call a metallurgy prof at the nearest Tech & Ag college and pick his/her brains...

[Kaweh]

Gjac wrote:
How hot does the engine get when climbing a hill? What is the temp reading on a flat?

Engine is steady at 120 on flat land and once I climb and the manifolds get hot it slowly creeps up to maybe160, or 180. But it doesn't overheat. Fan clutch motor works great.

[Kaweh]

ddndoug wrote:
kaweh - Have you tried "reading" the spark plugs to see if the air/fuel mixture is too lean? I'm guessing you already know this, but.... Are you disconnecting the timing advance wire while you are setting the base timing?

Doug

Yes exactly. timing is correct. I don't know about that spark plug reading. We have a snap on computer and so the GM shop foreman agreed to come on a test drive with me and do some data logging to what is happening at the moment they start to glow. At idle he said it was running a bit rich. not too much though he said. he wasn't worried about it. But I believe what is happening up a hill it's leaning out. we'll see early next week.

[Gjac]

How hot does the engine get when climbing a hill? What is the temp reading on a flat?

[ddndoug]

kaweh - Have you tried "reading" the spark plugs to see if the air/fuel mixture is too lean? I'm guessing you already know this, but.... Are you disconnecting the timing advance wire while you are setting the base timing?

Doug

[Kaweh]

Does your fan clutch come one with a loud roar when climbing a hill on a hot day? What is your timing set at?

Yeah Man, the fan works. 12 degrees advance. Everything works, no engine codes. great power in the city. Engine starts to drag up the hill, giving more fuel makes exhaust glow.

[Kaweh]

thanks for all the info everyone. The timing is correct because I even did it by ear and waited til it pings then backed it off. It is possible that they got a little red before but whey then all of a sudden after the backfire did my air line going to the air horns pop?
That should have happened six years ago, the first time it climbed to Reno and I went up the grapevine to L.A.

[SCVJeff]

Camreal wrote:
454s are also famous for cracking the exhaust manifolds too.

That too..

[Gjac]

I have a 96 GBM MH with a 454 TBI and when I bought it it ran very hot. Replaced leaking exhaust manifold gaskets. 2 years later manifold themselves cracked. Replaced with Thorley headers. Prior to installing headers I created an air dam to force air through radiator and added air ducts to to each side of the manifolds to cool the exhausts. This did little to help and may have caused the manifolds to crack by rain water entering ducts. Headers,FF muffler,CAI made a big difference in reducing the temps. Also don't neglect simple things like radiator,fan clutch and thermostat not opening up all the way. The radiator can be checked with an IR gun, from top to bottom, cold areas would indicate clogging. Look for a delta T of 50 degrees from top to bottom. Does your fan clutch come one with a loud roar when climbing a hill on a hot day? What is your timing set at?

[ferndaleflyer]

I used the big block Chev engines in our race cars ever since they came out in the 60s----headers get hot much quicker than exhaust manifolds and we learn quick not to "burn" a set of $2000 chrome headers. 1 thing is the plug firing before the exhaust valve is closed completely letting the combustion heat into the exhaust system (timing). The other is a lean fuel mixture. I tuned my fuel injected dragster using exhaust temp gauges in the headers and try to keep it in the 1100 to 1200 degree area for best performance and never see a red hot header. This is tuned to the lean side. Those manifolds should not be red hot so something is wrong somewhere.

[Jayco23FB]

rcmiller32 wrote:
Having worked on both the 427 and 454 GM V-8 engines in fire equipment over the years. Both will get glowing red hot exhaust manifolds when they are being worked hard. Have scene some get the exhaust red hot all the way down to the muffler.

The one poster about the harmonic balancer is correct. They fail making it very hard to set the correct timing.

X2 - I was a GM mechanic for 20+ years. I suggest replacing the balancer to make sure the timing is correct. Some manifold glowing is normal in the 454 under heavy load. The old 400 small block had the same issues.