Home » Public Forums » GMCnet » Exhaust smell
| Exhaust smell [message #108717] |
Thu, 16 December 2010 20:42  |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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I honestly grew up with vehicles that have more emissions standards then a 73 so pardon me for my ignorance. However the GMC is the smelliest vehicle I've ever owned.
Does everyones exhaust on these things stink so bad? I'd swear it runs rich but every mechanic says its running just fine. However do all vehicles without catalytic converters smell? I know if I install a catalytic converter it may loose horse power but will it smell better. Its not much a issue when its driving but sitting P.U.! LOL
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Exhaust smell [message #108724 is a reply to message #108721] |
Thu, 16 December 2010 22:45  |
Craig Lechowicz
Messages: 541
Registered: October 2006
Location: Waterford, MI
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Michael,
Yes, if you are used to vehicles with catalytic converters, all vehicles without them definitely produce more fumes. If it's really rich, it will burn your eyes, and if it's lean, it has a different smell, not sure how to describe it. A nice Saturday spent at our Woodward Dream cruise would make you very aware of this.
Modern (post 1980 or so) catalytic converters are 3 way catalysts HC, CO, and NOX and require the engine to be very near stoichiometric air fuel ratios all of the time to both be effective, and to have any kind of durability. That requires fuel injection and an oxygen sensor.
I think on cars the 75 - 79 catalytic converters were 2 way, and were more tolerant of varying fuel mixtures. If you got a medium duty truck converter prior to them going to fuel injection, (don't remember what years that covered) it might actually work, and I've thought about it a little.
It would save more air pollution than about a thousand or so new cars, as the standards today are so tight. But, heat shielding is a problem, and with all the vapor lock issues, I'm sure adding more under body heat would create a whole can of worms.
Craig Lechowicz
'77 Kingsley, Waterford, MI
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| Re: Exhaust smell [message #108728 is a reply to message #108717] |
Fri, 17 December 2010 00:58 |
jtblank
Messages: 237
Registered: June 2007
Location: Tulare, CA
Karma: 1
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Michael,
I know what you mean about the smell, my '76 was stinking bad and also had a idle miss when warm, after talking to Jim K he thought it might be the throttle plate to intake gasket leak, spraying carb cleaner verified the leak (increase in RPM) so I decided to rebuild my carb. My throttle plate shafts had a bit of slop in them so I installed a bushing kit to fix that, now after the rebuild it runs better than it ever has in the six years I've owned it and the exhaust tone and smell are totally different. The smell is now what I would call normal, I too think your problem is your GMC is lean. Also when I rebuilt the carb I re-jetted the primaries to #72's, it had #70's and although I haven't gone on a out of town trip to check mileage, I perceive a bit more power and definitely smoother running and acceleration.
HTH
John Blankenship
'76 Palm Beach
Tulare, CA
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| Re: Exhaust smell [message #108729 is a reply to message #108717] |
Fri, 17 December 2010 01:14 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| Mr.RadioActive wrote on Thu, 16 December 2010 18:42 |
I honestly grew up with vehicles that have more emissions standards then a 73 so pardon me for my ignorance. However the GMC is the smelliest vehicle I've ever owned.
Does everyones exhaust on these things stink so bad? I'd swear it runs rich but every mechanic says its running just fine. However do all vehicles without catalytic converters smell? I know if I install a catalytic converter it may loose horse power but will it smell better. Its not much a issue when its driving but sitting P.U.! LOL
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I think that another part of the trouble is that these engines don't have as tight a crank case as modern engines. When we sit at a stop light, the air intake for the cabin is just above the radiator and the radiator heat makes any fumes coming off the engine paint, oil on the engine or perhaps any blow by whiff right in. I have had two coaches that I wish smelled better when stopped. Both engines run well and don't use oil, etc. But they don't smell "fresh".
And, yes, the exhaust is pretty smelly. Folks can complain all they want about smog rules but a vehicle of the 70s puts out 85% more smog than modern vehicles. I have toyed with a catalytic on our coach but never mentioned it for fear guys would think I was crazy. From Springfield, MO, to Du Quoin, Max followed me and said my coach stinks, especially going down hill... and the fuel injection has the injectors turned off going down hill!
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Exhaust smell [message #108732 is a reply to message #108717] |
Fri, 17 December 2010 06:06 |
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jaholland
Messages: 565
Registered: June 2010
Location: Sweet Home Alebamy
Karma: 0
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| Mr.RadioActive wrote on Thu, 16 December 2010 20:42 |
I honestly grew up with vehicles that have more emissions standards then a 73 so pardon me for my ignorance. However the GMC is the smelliest vehicle I've ever owned.
Does everyones exhaust on these things stink so bad? I'd swear it runs rich but every mechanic says its running just fine. However do all vehicles without catalytic converters smell? I know if I install a catalytic converter it may loose horse power but will it smell better. Its not much a issue when its driving but sitting P.U.! LOL
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Mr Radiactive;
By Pouring A 3oz Bottle Of BRUT In The Tank Every Time You Fill Er Up
Will Make Er Smell Different ~
~ It'll 'Smell Like A Man'~ LOL
~ Joe ~
{and maybe correct any fuel delivery problem also}
/_]*[__][] *[__|] ~ * '73 TZE063V101887 "
"
O----------OO--]* ~ '78 TZE168V100234 "
"
" Joe & Lavelle " "
"
'sweet home alebamy'
[Updated on: Fri, 17 December 2010 06:08] Report message to a moderator |
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| Re: Exhaust smell [message #108744 is a reply to message #108717] |
Fri, 17 December 2010 08:49 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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I'd almost think about pouring some Brut in the tank! lol
Its not when I'm driving or really even sitting at a light that bothers me. I have more seals on the hatch then a sub. But when I'm working on it at the shop while its running or even for some reason we have to let it run while at a campsite if you leave the door open the exhaust stinks.
I had a mechanic extend the tailpipe thinking it would help alittle. Maybe it did slightly. I need to invest in some fabreeze!
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Exhaust smell [message #108747 is a reply to message #108744] |
Fri, 17 December 2010 09:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Michael, If your gasoline sits for long periods unused in your tanks,
especially out in the heating and cooling cycles of the sun, it will go bad.
It will stink so bad you will think a family of skunks has inhabited your
motorhome. The best catastrophic converter in the world won't clean up that
smell. If you have a rag with any of that gas on it, it will stink forever.
How old is the gas in your tanks?
Jim Hupy
Salem, Or
78 Royale 403
On Fri, Dec 17, 2010 at 6:49 AM, Michael <radioactive626@msn.com> wrote:
>
>
> I'd almost think about pouring some Brut in the tank! lol
>
> Its not when I'm driving or really even sitting at a light that bothers me.
> I have more seals on the hatch then a sub. But when I'm working on it at the
> shop while its running or even for some reason we have to let it run while
> at a campsite if you leave the door open the exhaust stinks.
>
> I had a mechanic extend the tailpipe thinking it would help alittle. Maybe
> it did slightly. I need to invest in some fabreeze!
> --
> 1973 23' Sequoia-
> Michael, Casa Grande, AZ
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| Re: [GMCnet] Exhaust smell [message #108748 is a reply to message #108744] |
Fri, 17 December 2010 09:58 |
Charles
Messages: 455
Registered: January 2004
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Michael,
Have you up graded to an HEI distributor. It helped
on my 73. I "think" it gave a hotter spark there by
burning some of the stink. Notice: think is in quotation
marks. I do know it started quicker and ran smoother.
Charles
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Charles Wersal
Duncanville, Texas
26 foot 1975 Glenbrook
Pandora's Box
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| Re: [GMCnet] Exhaust smell [message #108749 is a reply to message #108748] |
Fri, 17 December 2010 10:28 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
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It sounds to me like you have an exhaust leak somewhere near the engine compartment, or could it be that you have not yet blocked your intake manifold crossovers?
Sitting at idle my coach used to stink of exhaust fumes too, 'till I took it to a local muffler shop and replaced the mufflers. I was looking for a cheap fix and this did the trick. He replace a small section of tailpipe too, but the new mufflers made a huge difference. I haven't blocked my crossovers yet, so sometimes in traffic, or after a long idle she will smell a little.
Larry Davick
The Mystery Machine
On Dec 17, 2010, at 7:58 AM, Charles wrote:
> Michael,
> Have you up graded to an HEI distributor. It helped
> on my 73. I "think" it gave a hotter spark there by
> burning some of the stink. Notice: think is in quotation
> marks. I do know it started quicker and ran smoother.
> Charles
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: Exhaust smell [message #108794 is a reply to message #108717] |
Fri, 17 December 2010 20:34 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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Gas is new, I've had to fill up several times in the past few mths.
I just wondered if it was normal. Like I said honestly this is the only vehicle I've owned thats from the 70s.
Its not bad at all when driving. I ((did)) have a zillion exhaust leaks, but I think they are all fixed. I may have one tiny leak somewhere still but if I do its no concern as its so small I can't hear it all the time. I had horrible exhaust issues but a shop fixed all them. At my shop I've been working on the gmc a lot. So I've been starting it up alot. And idling if I leave the door open the breeze always blows the fumes in to the cabin.
I have a rebuilt Holly with only maybe 500 miles on it. I'm not sure if its adjusted exactly right for the gmc. But everyone that does hear my engine says it sounds good- I'm sure it could be adjusted better and optimized for a gmc but who knows!
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Exhaust smell [message #108830 is a reply to message #108823] |
Sat, 18 December 2010 09:11 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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| Steven Ferguson wrote on Sat, 18 December 2010 06:18 |
No hotter spark. The coil will do the minimum necessary to jump the plug gap, no more. Folks who buy "hot" coils or other magic gizmos are wasting their money.
However, an MSD box will fire each plug 5 times in one cycle up to a certain rpm and that definitely helps performance.
--
Steve Ferguson
Sierra Vista, AZ
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Steve,
I kind of hate to tell you this, but an MSD box will not do most of what is the folklore.
It will fire maybe three times in the idle region and once above that maybe two but, at road load it is no better than any other CDI box. Even when it does the multi-fire, the later sparks are so late that they are of little value even if the first spark didn't start a fire.
The practical matter is that the Kettering ignition - introduced in the Cadillac in 1910 - used until 1974 in our coaches has a long list of deficiencies. At the time it was developed, it was remarkable. It was the big thing until the electric self-starter (Cadillac 1912), sliced bread (1928) and canned beer (1935).
Conservation of energy works here, too. In most ignitions (including HEI), the coil accumulates and stores the energy that is released to fire spark plugs. You can't fire the plugs harder with a "hot" coil without working the the rest of the system harder as well. (This is why the wide gap will blow-up an HEI system.)
A wide gap or a hotter spark will never show an improvement in WOT performance on a test stand. The fire either starts or it does not. (End of that discussion)
The thing that will happen with more spark is fewer mis-fires. That will show up as improved fuel rate and lower HC emissions.
With all of this, I have to include that all the spark energy is a lost cause if the spark does not start the fire at the correct time.
Matt (the dyno lab refugee)
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Exhaust smell [message #108834 is a reply to message #108830] |
Sat, 18 December 2010 10:05 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Hey Steve & Matt, When I went to Mercury Outboard Training, they were all
puffed up with self importance over developing the Mercruiser CDI. They were
impressed with the fact that the CDI was not hampered by something called
coil saturation and rise time, and that they had tested their electronic
masterpiece to 15000 RPM with no misfire and more secondary energy available
the higher the rpms rose. They charged the primary side of the coils with
the output from a very specialized capacitator, and triggered it's timing
with a hall effect circuit using transistors. I have been on the receiving
end of that secondary discharge enough times to know that your elbow will
ache for long enough to remind you not to do that stupid trick again. I have
seen over 65KV on a scope hooked up to that system using surface gap plugs.
That system fires 2 stroke mix better than anything I have ever encountered,
and lean mixtures also. You are correct that conventional coils only produce
enough voltage to ionize the air gap in the plug and at that point the
voltage rises no higher. With a .030" plug gap with "normalized mixture" and
compression ratios around 9:0 - 1, that will be somewhere around 9KV, give
or take. Even though the coil may be capable of producing much higher
voltages, the plug gap & resistance in the secondary circuit determines the
discharge voltage. Just my two cents worth.
Jim Hupy
Salem, Or
78 Royale 403
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| Re: [GMCnet] Exhaust smell [message #108943 is a reply to message #108830] |
Sun, 19 December 2010 07:18 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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Matt,
Good explanation. I am aware of the shortcomings of the MSD with higher
rpms. However, it is still better than most systems when installed properly
on a good engine. It was never meant to be a bandaid for poor performance
and I should have said that. It is more of a racing product than anything
else as most race cars are working in a pure WOT, enrichment environment
most of the time and multiple spark discharge keeps a lot of bad things from
happening.
The MSD 6AL is about the best thing that can happen to a GMC that is driven
in mixed altitudes. Best thing other than computer controlled fuel and
ignition, that is.
On Sat, Dec 18, 2010 at 8:11 AM, Matt Colie <mcolie@chartermi.net> wrote:
>
>
> Steven Ferguson wrote on Sat, 18 December 2010 06:18
> > No hotter spark. The coil will do the minimum necessary to jump the plug
> gap, no more. Folks who buy "hot" coils or other magic gizmos are wasting
> their money.
> > However, an MSD box will fire each plug 5 times in one cycle up to a
> certain rpm and that definitely helps performance.
> > --
> > Steve Ferguson
> > Sierra Vista, AZ
>
> Steve,
>
> I kind of hate to tell you this, but an MSD box will not do most of what is
> the folklore.
>
> It will fire maybe three times in the idle region and once above that maybe
> two but, at road load it is no better than any other CDI box. Even when it
> does the multi-fire, the later sparks are so late that they are of little
> value even if the first spark didn't start a fire.
>
> The practical matter is that the Kettering ignition - introduced in the
> Cadillac in 1910 - used until 1974 in our coaches has a long list of
> deficiencies. At the time it was developed, it was remarkable. It was the
> big thing until the electric self-starter (Cadillac 1912), sliced bread
> (1928) and canned beer (1935).
>
> Conservation of energy works here, too. In most ignitions (including HEI),
> the coil accumulates and stores the energy that is released to fire spark
> plugs. You can't fire the plugs harder with a "hot" coil without working
> the the rest of the system harder as well. (This is why the wide gap will
> blow-up an HEI system.)
>
> A wide gap or a hotter spark will never show an improvement in WOT
> performance on a test stand. The fire either starts or it does not. (End
> of that discussion)
>
> The thing that will happen with more spark is fewer mis-fires. That will
> show up as improved fuel rate and lower HC emissions.
>
> With all of this, I have to include that all the spark energy is a lost
> cause if the spark does not start the fire at the correct time.
>
> Matt (the dyno lab refugee)
>
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumiere (say show-me-air)
> SE Michigan - DTW 3.2/4R
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
Sierra Vista, AZ
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| Re: Exhaust smell [message #109025 is a reply to message #108717] |
Sun, 19 December 2010 17:10 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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If it's not missfiring then I wouldn't blame the ignition. I would adjust the carb to make sure that is correct at idle if that is the main stinky time. I think that best would be max lean idle speed at full warm temp and then (I'm guessing) 25 RPM lean drop per side (each screw). This should be the optimal trade for smooth idle and emissions. The working (rare) Thermac preheat may also help with vaporization especially if the heat riser is defeated. That's how mine is setup and though it's a 77 HEI, the "nose" is pretty good for a non cat engine. I know how just a slight missadjust can really increase emissions and I wish that more classic car collectors would pay more attention to this for cruises. Luckily, good running and low emissions usually go hand in hand. Also the timing may effect the stink factor. The new cars are pretty amazing and just spitting out H2O and CO2 and idling smoothly.
John Lebetski
Woodstock, IL
77 Eleganza II
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