Glowing hot manifolds
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: Glowing hot manifolds (PeteL)
Pete..that was uplifting and commendable.
BTW: I say he has a basic tune up problem or worn engine components ( like valve springs ).
BTW PS: I am NOT grumpy...Ok! :boxing
BTW PPS: I hope I'm not considered old, I'm only a young 35. :D
BTW: I say he has a basic tune up problem or worn engine components ( like valve springs ).
BTW PS: I am NOT grumpy...Ok! :boxing
BTW PPS: I hope I'm not considered old, I'm only a young 35. :D
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: Glowing hot manifolds (PeteL)
I am looking into the part of the lean running hotter...which is true to a certain extent, only when true stoichiometry is met, that is where the HOTTEST burn will occur, cars are designed to run slightly richer than that point because of metal fatigue/failure becomes a problem. Also, if you run too rich, cylinder tempreatures go down, and the unburned fuel will continue to burn in the exhaust, causing the exhaust temperature to be too high.
As a short side topic, the AIR system on the L98's was to serve two purposes, one was to inject air into the exhaust manifolds when the engine was cold and spitting out raw fuel to promote it burning in the exhaust manifolds so that it would not saturate the cat converters and make them overheat prematurely when the engine does get to temperature.
As a short side topic, the AIR system on the L98's was to serve two purposes, one was to inject air into the exhaust manifolds when the engine was cold and spitting out raw fuel to promote it burning in the exhaust manifolds so that it would not saturate the cat converters and make them overheat prematurely when the engine does get to temperature.
Racer
Joined: Aug 2001
Posts: 478
Likes: 45
From: St. Louis
Re: Glowing hot manifolds (vettemech85)
You are getting plenty of responses for cats, and that's my guess (almost). My precats let go and sent their material downstream, where it plugged up the exhaust at the main cat. The engine would rev to redline at idle, but put it under load (just drive and hit the gas from low speed) and it would flatten out at about 3100 rpm. From there it made no power, smoked black out the tailpipe, and missed. There were no codes and fuel pressure and vacuum were good. I cleaned out all the crud and remounted the exhaust - no more problems. A cheap fix and a great place to start. Very common on L98s.
[Modified by TomH91, 11:09 PM 1/22/2002]
[Modified by TomH91, 11:09 PM 1/22/2002]
Drifting
Joined: Jun 2001
Posts: 1,997
Likes: 1
From: Lake Ozark MO
Re: Glowing hot manifolds (vettemech85)
BBA... you've been dogged.... by ME (wink)... http://forums.corvetteforum.com/zerothread?id=224055
Le Mans Master
Joined: Nov 1999
Posts: 7,687
Likes: 2
From: San Antonio TX
Re: Glowing hot manifolds (Nathan Plemons)
Pete...dead wrong. Only fuel burning in the manifold will make it glow red. Nothing else will, PERIOD.
I guess all the people who have had the exact same symptoms out of a clogged cat were just imagaining it?
I guess all the people who have had the exact same symptoms out of a clogged cat were just imagaining it?
I should know, it happened to my L98.
[Modified by LT5FIRE, 8:27 PM 1/23/2002]
Racer
Joined: Oct 2000
Posts: 460
Likes: 0
From: Lincoln NE
Re: Glowing hot manifolds (BBA)
I gotta chime in too, I would have to go on the side of a rich mixture being a possibility. When I fired mine up for the first time after a long time just this weekend, I made sure the timing was correct. Then I had the wife run the RPM's up to about 1500 RPM to make sure the cam lobes were getting oiled properly (just breaking it in). Before the engine got into closed loop, the manifolds started glowing. I would assume I was at a rich condition since the engine wasn't fully warmed. The condition went away once the engine warmed up.
I'd seen that before on a carbureted car that was idling too long with the choke plate closed and the throttle on the fast idle cam. The cat gave off a nice glow also that went away soon after I kicked it down. Now that one I know was running a rich mixture.
Leaning a fuel mixture will increase the exhaust gas temperature to a point. Getting the manifolds to glow would require some extra combustion in the exhaust though (don't know about the clogged catalytic thing, never seen it).
Just my $.02 worth, about all it's worth too.
I'd seen that before on a carbureted car that was idling too long with the choke plate closed and the throttle on the fast idle cam. The cat gave off a nice glow also that went away soon after I kicked it down. Now that one I know was running a rich mixture.
Leaning a fuel mixture will increase the exhaust gas temperature to a point. Getting the manifolds to glow would require some extra combustion in the exhaust though (don't know about the clogged catalytic thing, never seen it).
Just my $.02 worth, about all it's worth too.
Drifting
Joined: Dec 2000
Posts: 1,851
Likes: 5
From: Liberal Kansas
Re: Glowing hot manifolds (ToddAT)
My experience is with engines that have computer controlled fuel management systems. Along with the electronics these engines have pyrometers to monitor exhaust and converter temps as well as having emission monitoring equipment.
Without other engine problems, fuel mixtures on the lean side cause higher combustion temps and lower exhaust temps. (remember lean mixtures melt pistons) The A/F energy is spent in the cylinder.
As the mixture richens the combustion temp will decrease and exhaust temp will increase. There is incomplete combustion in the cylinders with the remainder of the fuel being burned in the exhaust.
Late or retarded timing has a similar effect as the rich mixture. The A/F mixture is ignited too late in the cycle of events for a complete burn in the cylinder and therefore finishes the burn in the exhaust.
As other have stated the ole clogged converter is suspect also.
Dan
Without other engine problems, fuel mixtures on the lean side cause higher combustion temps and lower exhaust temps. (remember lean mixtures melt pistons) The A/F energy is spent in the cylinder.
As the mixture richens the combustion temp will decrease and exhaust temp will increase. There is incomplete combustion in the cylinders with the remainder of the fuel being burned in the exhaust.
Late or retarded timing has a similar effect as the rich mixture. The A/F mixture is ignited too late in the cycle of events for a complete burn in the cylinder and therefore finishes the burn in the exhaust.
As other have stated the ole clogged converter is suspect also.
Dan
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: Glowing hot manifolds (Dan Plett)
I agree clogged cats WILL make the mainfold/bolts glow.
I should know, it happened to my L98.
I should know, it happened to my L98.
Dan,
My experience is with engines that have computer controlled fuel management systems. Along with the electronics these engines have pyrometers to monitor exhaust and converter temps as well as having emission monitoring equipment.
As for the LT1, the later ones ( some 94, 95-96 I think ) have OBD II systems that use O2 sensors before and after the cat, with no temp sensor for the cat. on most, but I have seen a few cars with a single over temp warning switch.
[Modified by BBA, 12:50 AM 1/24/2002]
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Drifting
Joined: Dec 2000
Posts: 1,851
Likes: 5
From: Liberal Kansas
Re: Glowing hot manifolds (BBA)
Dan,
You won't find the first pyrometer on a L98 engines exhaust system. None at all. The only thing that monitors an L98 engine mixture is the single O2 sensor.
As for the LT1, the later ones ( some 94, 95-96 I think ) have OBD II systems that use O2 sensors before and after the cat, with no temp sensor for the cat. on most, but I have seen a few cars with a single over temp warning switch.
Combustion characteristics from the engines I work on are the same as the Corvette. Therefore a change in A/F ratio and timing will have the same effect. As stated, the engines I work with do have all the monitoring sensors. Very cool!
The reason for the reply in the first place was a misconception of a few on the effects of a lean or rich A/F mixture.
Have a good day.
Dan
