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1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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85 Posts
Discussion Starter #1
After just a few seconds of my 91' 4.9 sedan deville 157,000 idling , the exhaust fumes and pipe is so hot u can barely touch it. Is this normal? I cut the convertor off today, and could see thru it, gonna strait pipe it tomorrow.

Thanks, John
 

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1991 Deville, 1995 Deville
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220 Posts
how hot are you talking. i had retarded ignition timing and the exhaust manifolds were red after 5 mins. if its just too hot to touch where it makes a little burn, that is normal. your car will be fine with a straight pipe.
 

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1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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85 Posts
Discussion Starter #4
The manifolds are not glowing i dont think, but its hotter than just about any car i can ever remember fooling with. Retarted timing huh? It does have a "rich" smell coming out of the tailpipe, especially when it gets warmed up, and the strait pipe didnt help either.
 

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'85 Fleetwood FWD
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728 Posts
One item that may make it run rich is a bad oxygen sensor. It may not be bad enough to show a code etc, but still make it run a bit rich.
 

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1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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85 Posts
Discussion Starter #6
One item that may make it run rich is a bad oxygen sensor. It may not be bad enough to show a code etc, but still make it run a bit rich.
I heard an oxygen sensor does not work until the motor warms up, is this true? But i am getting an o2 sensor code.
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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2,026 Posts
Its going to loud as sh*t with that straight pipe unless you still have the stock muffler. I had the flowmaster camaro muffler on mine, then I replaced the cat with a straight pipe... It went from a nice throaty purr to "OMG wtf have I done?!" I ended up replacing the straight with a cherry bomb.
 

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1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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85 Posts
Discussion Starter #8
Its going to loud as sh*t with that straight pipe unless you still have the stock muffler. I had the flowmaster camaro muffler on mine, then I replaced the cat with a straight pipe... It went from a nice throaty purr to "OMG wtf have I done?!" I ended up replacing the straight with a cherry bomb.
hahaha!! No I still have the stock muffler, sounds just the same, little rattle from the baffles working loose, but that was going on before.
 

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1990 Cadillac sedan devile
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616 Posts
Its going to loud as sh*t with that straight pipe unless you still have the stock muffler. I had the flowmaster camaro muffler on mine, then I replaced the cat with a straight pipe... It went from a nice throaty purr to "OMG wtf have I done?!" I ended up replacing the straight with a cherry bomb.
so what did it sound like with the strait pipe and the flowmaster together ? and did you lose any mpg's
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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2,026 Posts
I actually lost a couple mpg's and acceleration suffered a bit. After 2000rpm I could hear a high pitched "whack whack whack sound". It was really awful. I replaced the straight pipe with a 1 3/4" glass pack to replicate the backpressure of the cat. Now I get the best mileage I've ever had! I think the smaller diameter creates a venturi effect to increase exhaust scavenging. I avg from 22 - 24mpg in town and 27-28 highway. Its still louder than "what a caddy should sound like" but I'm not one to do something just because certain people think it 'should' be a certain way.
 

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1990 Cadillac sedan devile
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616 Posts
I actually lost a couple mpg's and acceleration suffered a bit. After 2000rpm I could hear a high pitched "whack whack whack sound". It was really awful. I replaced the straight pipe with a 1 3/4" glass pack to replicate the backpressure of the cat. Now I get the best mileage I've ever had! I think the smaller diameter creates a venturi effect to increase exhaust scavenging. I avg from 22 - 24mpg in town and 27-28 highway. Its still louder than "what a caddy should sound like" but I'm not one to do something just because certain people think it 'should' be a certain way.
cool bet it sounds nice i might do the same to mine . 27-28 mpg would be sweet i only get about 24-25 hwy and 15-17 town with my 90
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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2,026 Posts
Well I have low mileage and advanced timing which probably plays a part. Its still louder than with the cat + the flowmaster. I honestly wish I hadn't gutted the cat.
 

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1990 Cadillac sedan devile
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616 Posts
my car has about 140,000 on the body and about 175,000 on the engien . as far as being loud i really don't mind it to much i got about 1,500 stereo to drown it out if i want lol . summer project hear i come
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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2,026 Posts
When I want it quieter, I just put a plumbing test plug in the drivers side tailpipe. It's like a heavy duty balloon that you pump up with air, known as a 'test ball'. It makes a huge difference. Of course this only works on crossflow-style mufflers. I plan to put an electric cut-out on it in the future so I can change the sound from the driver's seat.
 

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1990 Cadillac sedan devile
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616 Posts
whear did you get you 1 3/4 glasspack i cant seam to find one . i thought about just useing a 2 1/ then reduceing it at the end to 1 3/4 and then back to 2 1/4
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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3,310 Posts
My Deville has a gutted cat ( PO ) and the stock muffler has a raspy performance tone to it now. I guess they are corked up in two places and you can free up one or the other.
 

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Hey Sevillian, what exactly did you do? I would be really happy to get more miles per gallon out of my car because I drive 100 miles a day.
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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2,026 Posts
Hey Sevillian, what exactly did you do? I would be really happy to get more miles per gallon out of my car because I drive 100 miles a day.
replaced stock muffler with flowmaster dual > got greedy and gutted cat > WAY too loud > replaced cat with 1 3/4" glasspack > better pickup and +3mpg but still a little loud.
 

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1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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85 Posts
Discussion Starter #20
dude, im only gettin about 13.8 mpg or so in the city, round 22-24 on the highway, is that normal? 91' 4.9, 150xxx miles
 
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