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Old 06-11-2019, 03:33 PM   #1
Loco83
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Failed Smog

In the the 36 yrs of ownership her first smog fail
Took the truck in this morning for her Biennial test and she failed.
HC (PPM)
Max Meas
135 172

CO%
Max Meas
O.95 1.26
Did the tune up, plugs, cap/rotor, air filter, cleaned out the PCV valve and oil change. Sprayed the E4ME Qjet out with GUMOUT as well as spraying down the throats with the engine running. Took her out on the highway for a 10 mile high speed run at 70, no joy.
Tech suggested a carb adj, and new plug wires.
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Old 06-11-2019, 03:52 PM   #2
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Re: Failed Smog

yep, adjust carb and check for vacuum leaks, both no charge

wires would complete your recent tune-up but you should go back and inspect the new components as well..

if the engine is otherwise healthy [good compression], may be time for a cat..

even if that's not the sole cause, may improve the tailpipe test adequately to pass

good luck!
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Old 06-11-2019, 04:31 PM   #3
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Re: Failed Smog

I've always used a couple of bottles of gas line antifreeze in about 1/4 tank before I go in for smog tests.
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Old 06-11-2019, 05:05 PM   #4
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Re: Failed Smog

MSD boxes and the like can help too.
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Old 06-11-2019, 07:49 PM   #5
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Re: Failed Smog

Put in a sleeve of Lucas Oil fuel injector cleaner in the tank with 87 octane gas and you will pass.
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Old 06-12-2019, 11:03 AM   #6
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Re: Failed Smog

Here is a 5 gas chart to help understand how changing your tune will change emissions.



I would say it is running a little rich. Certainly check all vacuum lines and set the idle mixture screws on the carb. Make sure the choke is fully off. Might look into the EGR valve.
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Old 06-12-2019, 12:17 PM   #7
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Re: Failed Smog

Thank you Gents.
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Old 06-12-2019, 12:22 PM   #8
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Re: Failed Smog

Warmer thermostat could also help if you are real close.
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Old 06-24-2019, 03:29 PM   #9
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Re: Failed Smog

Well took her in for a third smog check and she started smoking like crazy, needless to say it was a no go, place is a smog and repair shop, talked with the mechanic and sound like the valve guide seals, truck did blow smoke on start ups for the last ten yrs and my last smog check it just passed by 1%, waiting for a call to see what they find, getting too old to mess with the repairs
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Old 06-24-2019, 04:04 PM   #10
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Re: Failed Smog

Quote:
Originally Posted by Killer Bee View Post
yep, adjust carb and check for vacuum leaks, both no charge

wires would complete your recent tune-up but you should go back and inspect the new components as well..

if the engine is otherwise healthy [good compression], may be time for a cat..

even if that's not the sole cause, may improve the tailpipe test adequately to pass

good luck!
compression and leak down tests should confirm their diag..

might be better off looking into a crate long block since it's a stocker that has to smog..

head work in the truck may pan out more $$ in labor then swapping it out whole..

hopefully fairly inexpensive and breathe new life into it for several more years without continuing smog issues..

my '02 GMC had the weak head issue and was eventually drinking a gallon of coolant a week..

at ~150k miles made more sense to go long block crate than dumping lots of $$ of head R&R on top of a half worn out short block..

good luck!
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Old 06-24-2019, 05:18 PM   #11
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Re: Failed Smog

Thanks, i'll talk to the mech when he calls me back.
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Old Yesterday, 10:43 AM   #12
truckin 79
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Re: Failed Smog

I am dealing with the same thing on my 79, what a pain in the rear. I bought a wide band gauge with O2 sensor in exhaust. I thought this would solve all my problems and at 200 installed be cheaper then taking to a mechanic. Well I think my truck is messing with me. When I adjust idle mixture screws and reach that magic number of 14.7/1 to 15/1, then drive it around it goes rich on me to around 13.5/1 when I come back from a drive. I try to lean it out and almost seems like it gets richer on drives. I just have to pass idle and at 2000 rpm, I am going to take it this week and see how close 13.5/1 (12.5/1 is supposed to be power range) gets me, third time is a charm. The truck actually drives pretty good, better then it ever has, without that thick smell of exhaust that burns your eyes. The tech here in CO said it is hardly ever the catalytic converter since limits are so high for older vehicles and should essentially pass even if vehicle had no converter.
Anyway back to yours, it does not seem that you are that far( mine was way off the first 2 times I took it) off and would think idle mixture screw adjustment would get you there.
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Old Yesterday, 12:33 PM   #13
rpmerf
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Re: Failed Smog

Quote:
Originally Posted by truckin 79 View Post
Well I think my truck is messing with me. When I adjust idle mixture screws and reach that magic number of 14.7/1 to 15/1, then drive it around it goes rich on me to around 13.5/1 when I come back from a drive. I try to lean it out and almost seems like it gets richer on drives.
A couple things to be aware of here. Fuel temperature makes a big difference. Manifold temperature makes a difference, but not as much. You also have to consider under hood temps. The hotter it is, the richer it will be. That might be why it is good when sitting idle, then rich after a drive.

Be aware of your power piston. Make sure it is bottomed out at idle in drive. You can take a small rod down the vent hole and feel the power piston. Try this with the engine off so you can feel it push down against the spring. Start it up, put it in drive, and see if it is pulled all the way down, or if you can push it down further. I'm wondering if leaning it out has it running at lower vacuum, opening the power piston sooner.

Don't forget to set your ignition timing.
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Old Yesterday, 01:16 PM   #14
truckin 79
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Re: Failed Smog

Well now that you say that about power piston and making sure it is all the way down. When I rebuilt this carb a few months ago, I found a broken pencil inside of vent tube. I thought to myself what kind of idiot has been working on this carb. Maybe they were using the pencil to keep power piston pushed all the way down.
Sorry loco83 did not intend to jack your thread.
Thanks rpmerf for the info
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Old Yesterday, 03:21 PM   #15
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Re: Failed Smog

No problem
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