Sad Day - Failed Emissions

Agoogol

Agoogol

Active member
Aug 16, 2019
295
79
28
Centennial CO
Me being the dumb bad owner/purchaser I neglected to get the PO to get an emissions test. I take it down, and of course it fails. 403 Oldsmobile in a
77 Kingsley.

At idle the CO% was 7.23 with a limit of 5.5. Everything else was well wiyhin range.

I had done a new air filter and uel additiive to be on the safe side, but still not good enough.

So now I will do a quick tuneup, PCV valve, plugs, oil.

But what else can/should I do? I would think there must be some carb adjustment to be done for the idle carbons. Either that or perhaps a vacuum leak
somewhere?? I am not very knowledgable in this area, so any suggestions will be taken seriously! Esoecially from anyone here in CO who wants to come
by and lend a hand! LOL!
--
Kevin
1977 Kingsley
Centennial CO
 
There should be 2 mixture screws on the front of the carb base....you could screw them in a touch....best way is with a vacuum gauge attached or a
tachometer.

Normally you back them out till you saw the max vacuum or the idle start to drop....then you would screw them in till you saw that again ....set in
middle.

If you dont have either just turn them in till the idle just starts to drop.....just remember how much so you can put it back.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
The heating & A/C controls on our coaches frequently leak. Try disconnecting the vacuum to those controls and block the fitting on the manifold
during the test. Hook it back up afterward and fix the leaks later. Worked for me!
--
John Shutzbaugh, Vacaville, CA, ncserv;
77 Eleganza, bought it new, can't blame PO; and
78 Buskirk stretch, "What were we thinking?"
 
a good tune up is one place to start. Not a bad idea no matter what, to make sure you are positive your cap, rotor, plugs, plugwires are all
perfect, as well as make sure all the vacuum lines are in good shape and attached where they are supposed to be. a good running GMC as I understand
will have no issue passing smog. I would be a little nervous about randomly turning screws, but if you find someone that understand the coach and
that q-jet. but many people do more harm then good.

Hopefully someone local can help you out who had had to deal with this situation. One big benefit of being active in a club, so maybe reach out to
join the local club? Jim K and miguel out in california has some knowledge on emissions passing.

--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
Generally speaking if you fail an "E" test changing the oil is usually the best bang for the buck and will usually get you passed.

A tune up never hurts either but if someone gaps the plugs wrong it will hurt you more so make sure to set them....not just install out of box.

There are other tricks that i know but they are more invasive and best left to someone who is a mechanic.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
Too rich on idle. Improperly set idle air mixture screws a possibility.
Also misfiring plugs can do the same thing. If they are old, make sure you
replace them with one heat range hotter plug, FOR THE EMISSION TEST ONLY.
Check the gaps. No bigger than .045". Check the wires, rotor, and cap. Any
doubt, throw them out and replace with high quality replacement parts.
JWIWD.
Jim Hupy
Salem, Oregon
78 GMC ROYALE 403

On Wed, Sep 4, 2019, 4:03 PM tonka6cuda6--- via Gmclist <

> Generally speaking if you fail an "E" test changing the oil is usually the
> best bang for the buck and will usually get you passed.
>
> A tune up never hurts either but if someone gaps the plugs wrong it will
> hurt you more so make sure to set them....not just install out of box.
>
> There are other tricks that i know but they are more invasive and best
> left to someone who is a mechanic.
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Check all vacuum hoses for correct patch and condition. Many POs repatch vacuum hoses because they don't understand the logic behind the GM engineers
design. Per factory manual you want a 50 RPM lean drop idle. That's exactly 25 from max best lean idle speed. Very critical to get the numbers down.
Also the advance mechanism in your distributor may be stuck and gummed uo with stiction. The AutoThermAC air cleaner preheat is important for fuel
mixture volatility and allows for leaner mixture. If bet that is disconnected
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
"At idle the CO% was 7.23 with a limit of 5.5. Everything else was well wiyhin range. "

7%+ is pretty rich, but this should be easy to fix. Since all other parameters were within spec, I think you can probably rule out bad plugs, bad
plug wires, bad valves, significant vacuum leaks, etc, all of which would tend to cause misfire, and resultant high HC readings.

Of course checking the timing (and the advance while you're at it) is a good idea, as the somewhat retarded stock setting helps with CO at idle.
Check the oil. If there's any trace of gasoline odor on the dipstick, then certainly change it. Make sure the choke is opening completely when
warmed up. Make sure the engine reaches operating temperature. (Some fool may have removed the thermostat.)

Most likely though, you'll find it just needs an idle mixture adjustment, maybe 1/4 to 1/2 turn leaner as several have instructed above. If you can
find a local shop with an infra-red exhaust analyzer willing to spend an hour or less on it (after you've checked the above items), they should have
no problem cleaning things up. Remember, just driving from low altitude to Denver's thinner air is enough to make it run rich.

HTH
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
 
So on my 455 the original heat riser for the choke had just about completely rotted off, so when I picked up the coach the choke was intermittent
causing all kinds of problems including two horrific explosions in the mufflers that blew them open (unburned fuel in the exhaust system). Am now
running an electric choke. I don't know if your engine has the same setup but I would check just to be sure..

Rich
--
Rich Kinas
1976 Elaganza II
Orlando, FL
 
Just wanted to say thanks for all the responses, since I forgot to!

In the end, I gave it an oil change, PCV and plugs. Started messing around with vacuum hoses and found two right on top of the carb that were super
loose and pulled right off...replaced those. All the bolts holding the carb down to the manifold were slightly loose, maybe a 1/4 turn on each and
snugged em up.

Passed with flying colors!

Except for the door lock getting stuck and the emissions guy having to crawl out the back window....but that will be another another post. :lol:
--
Kevin
1977 Kingsley
Centennial CO
 
Sometimes, it is the simple stuff. Glad you passed. So sorry you live in a
place where government officials do not realize the fact that the GMC is a
truck, and not subject to the same restrictions that passenger cars are.
But, good on ya, mate..
Jim Hupy
Salem, Oregon

On Mon, Sep 23, 2019, 4:59 PM Larry Davick via Gmclist <

> Excellent news - congratulations!
> --
> Larry Davick
> A Mystery Machine
> 1976(ish) Palm Beach
> Fremont, Ca
> Howell EFI + EBL + Electronic Dizzy
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Seems I remember a similar story about some GM officials and the first public showing of the GMC Motorhome.

> Just wanted to say thanks for all the responses, since I forgot to!
>
> In the end, I gave it an oil change, PCV and plugs. Started messing around with vacuum hoses and found two right on top of the carb that were
> super loose and pulled right off...replaced those. All the bolts holding the carb down to the manifold were slightly loose, maybe a 1/4 turn on each
> and snugged em up.
>
> Passed with flying colors!
>
> Except for the door lock getting stuck and the emissions guy having to crawl out the back window....but that will be another another post. :lol:

--
C. Boyd
76 Crestmont
East Tennessee
 
Given the restrictions on trucks a lot of places, I'd rather it wasn't considered one. Let me note though, no emissions test here where I live yet.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
I have learned a lot from the pros and from owners , so I can assist people
on the emission tests.
I need to see the test results before we can talk about it.

On Tue, Sep 24, 2019 at 5:19 AM Johnny Bridges via Gmclist <

> Given the restrictions on trucks a lot of places, I'd rather it wasn't
> considered one. Let me note though, no emissions test here where I live
> yet.
>
>
> --johnny
> --
> Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> I forgive them all, save those who hurt the dogs. They must answer to me
> in hell
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
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