Glowing Exhaust Manifolds 1992 454 TBI 7.4L P30 Motorhome

[Markmx6]

Just throwing this out there, is it possible that the catalytic converter is blocked up? maybe something else causing a restriction?

[Kaweh]

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

[Fast355]

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

Once upon a time I saw a GMC motorhome with the quadrajet fed oldsmobile 455 crack an intake manifold and under heavy throttle the crack would expand and hot exhaust gasses would shoot into the intake manifolds, leaning out the air/fuel mixture and cause the engine to run poorly and the headers to glow.

[Kaweh]

Once upon a time I saw a GMC motorhome with the quadrajet fed oldsmobile 455 crack an intake manifold and under heavy throttle the crack would expand and hot exhaust gasses would shoot into the intake manifolds, leaning out the air/fuel mixture and cause the engine to run poorly and the headers to glow.

Thanks for your thoughts! I put brand new exhaust manifolds on as part of my rebuild!!

[Fast355]

Thanks for your thoughts! I put brand new exhaust manifolds on as part of my rebuild!!

I am confused at how the exhaust manifolds have anything to do with the intake manifold.

What I was saying is the 455 Oldsmobile manifolds were known to crack under the carburetor in the exhaust crossover passageway and when the engine was working hard and hot the crack would expand and dump exhaust gasses right back into the intake charge.

[lionelhutz]

Did you confirm that the TDC mark on the balancer is actually TDC?

If you look-up the ultimate TBI mods you can find info on how to make the stock regulator adjustable. It's not as easy to adjust, but there is a screw you can release so you can make small adjustments without buying any parts.

[Kaweh]

The timing is correct and I tried it at 4 degrees TDC, 6 and 12. We also did it by ear once. When it started to knock we backed off a bit. And that's where it's at right
now, 12 degrees. Great power. just the harder I push it to go up a hill, the hotter they get. Supper bright! Some folks think this is normal and that chevys were prone to cracks and glowing exhausts because of the restrictive nature of the exhaust. They say maybe I didn't notice it. But this is scary red past the Y pipe. The GM foreman agreed to go on a test drive with me with his scanner next week so we'll go and see what he says. I say it's time for headers and dual 3" exhausts. Let's face it everyone I have been in touch says the design is poor and should have never been made like that and that is why in 96 GM changed it.

[jay72]

You're going to swap manifolds for headers so then you'll have glowing red headers.
On my '92 454 I have headers to dual 3" exhaust all the way back to the bumpers. What I said before about GM changing to a steel "shorty" header type manifold, the point is steel is less prone to crack. IMO headers are more likely to glow red because they're thinner than cast iron manifolds.
Heres a video I made several years ago, this is whats going on inside your exhaust. https://youtu.be/CLYi4JDnTSQ
And BTW, haven't changed anything on that engine since, except oil and filters, and it's been run several times for 24 hours straight fully loaded in the bed while towing a car on a trailer. Do I care if my headers are red? No I don't.

[Markmx6]

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

I gather that, but it doesn't mean it isn't causing a restriction. If you run raw fuel through a cat, it will clog up really quick. There are other things that can clog it as well. There could also be a restriction somewhere else.

[Kaweh]

I gather that, but it doesn't mean it isn't causing a restriction. If you run raw fuel through a cat, it will clog up really quick. There are other things that can clog it as well. There could also be a restriction somewhere else.

it's no the catalytic converter. I ran it for a month without the catalytic converter in it. IT is NOT the Cat.

[Nasty-Z]

Put a scan tool on it and watch the O2 readings , I believe I mentioned doing this in an earlier post .

I also questioned the validity of the "90 #/hr" injectors you installed , were these from a reputable source such as Mr. Injector , or parts store specials ?

You need hard data to find the problem , scan tool data , at this point I am lost , both here and on Chevytalk.

TOM