TRYING TO PASS SMOG

[clinebarger]

Without the test results.....Nobody is going to be able to help you!

Most 1985 C1500 trucks had a 700R4 4 speed overdrive, If it did have a 3 speed auto....It would be a TH375(light duty TH400), The TH350C was phased out in 1983.

 

[RedOakRanch]

Back in the 90's we used to pass around the smog carb to who ever needed it, then put the Holly back on when complete!

 

[earlyre]

Originally Posted By: Chris142
Originally Posted By: sleddriver
Calif. doesn't have a 25+yr old exemption?
no


If I am remembering correctly, the cali exemption cutoff is somewhere in the mid 70's?

yes, memory proven correct by google:
"Smog inspections are required unless your vehicle is: Gasoline powered 1975 year model or older. Diesel powered 1997 year model and older or with a Gross Vehicle Weight rating (GVWR) of more than 14,000 lbs."
https://www.dmv.ca.gov/portal/dmv/?1dmy&urile=wcm:path:/dmv_content_en/dmv/vr/smogfaq

 

[CT8]

Why isn't the vehicle passing smog?

 

[i_hate_autofraud]

I never had CRC or other stuff work, turns out running a little lean can cause a lean-miss you can't feel
yet you get hi HC and high NOx at the same time, etc,

Tiny vacuum leaks,,,,, the list goes on!

 

[StevieC]

I would do the following:

Oil Change, Tune Up with new plugs/wires/distributor etc. Check the PCV valve as well.

Check the timing and slightly retard it if possible. (Helps reduce NOx)

Adjust all the mixture screws on the carb (For Idle & Fast jets) to the lean position where the engine is stumbling and then forward (counting the turns) until it's too rich. Then back it off to the lean side of in-between these two points. (or just about 1/2 the turns between the too lean to too rich positions, leaning more on the lean side) This will put you in the Stoichiometric range close enough it should pass. (Do this on a fully warmed up engine only)

Ensure the choke is functioning properly and not throwing out the mixture.

Check that the EGR valve is working properly (if equipped)

Take it for a good long drive and then go and get it tested.

This should make most Carb equipped engines pass as long as the Catalytics are doing their job (if equipped).

 

[Ducked]

Heard of people running a high percentage of ethanol in the fuel as a temporary work-around. I suppose this is mostly just another way of leaning the mixture, but it would also raise the octane rating which one could in theory tune for.

I can't get idle below 1500 rpm, I THINK because the needle/jet is damaged, so I might try the ethanol trick if I had to pass a proper (government) emissions test.

 

[spasm3]

Originally Posted By: clinebarger
Without the test results.....Nobody is going to be able to help you!

Most 1985 C1500 trucks had a 700R4 4 speed overdrive, If it did have a 3 speed auto....It would be a TH375(light duty TH400), The TH350C was phased out in 1983.


Without all the numbers we are all guessing. We don't know if you barely failed or failed by a huge margin. We need to see all the numbers to tell you what to do.

We need the CO, HC and NOX readings, and at what rpm.

 

[StevieC]

Fast idle can also be a vacuum leak from tired vacuum hoses that are cracked/broken. This would also not bode well for an emission test.

 

[i_hate_autofraud]

If you're high on NOX only, typically it means your Cat is not working, dead.

Replacement aftermarket cats are disappointing.

I was able to rig the EGR to drop NOX at idle and the run test for smog:

1980's Chrysler 318 V8s:

- locate the EGR vacuum bleed valve solenoid. (usually on firewall)
- remove small air filter from valve
- place tape over bleed orifice, no gaps/leaks
- then poke a hole in the top of the tape with a needle, .030" dia (make hole bigger if EGR cycles too wide)
- you have 'rejetted' the orifice smaller to hold some vacuum to cycle the EGR during smog tests
- stick filter back over valve to hide tape.
- typically EGR valve starts to barely open with 2-3 inches of vacuum, that's what you want..
- there should still be a vacuum delay valve in line to the EGR, this will slow down "hunting".
- idle speed will slowly rise and fall as EGR opens and closes slowly, in my case it was slow enough
a distracted tech did not notice and passed the car with a dead cat! Tail pipe levels were legal!
- idle RPMs slowly oscillated between 500 - 575 RPMs
>> NOX dropped 800 ppms!! passed at just 220ppms


1990's V6 Chev Lumina cars: (with EGR mounted high on engine)

- unplug EGR cable
- unbolt EGR assy, (2 bolts- use PB Blaster as needed)
- separate carefully, so high temp gasket is not damaged
- use razor knife to cut a fine slot into the gasket from the exhaust to the intake ports
- slit should be .030" wide, .020" deep. don't overdo it.
- reassemble + cable, don't start w/o cable in or EGR code is set.
- reset OBDII if light was on (for a dead cat code)
- drive around for a day and then get smog tested before OBD light goes off
- did this on 2 luminas, NOX dropped 700ppms average
- tailpipe legal levels!

Originally, EGRs where expected to open only at higher RPMS under load, to pass
smog and get rid of hi NOX you need "uncommanded" EGR at idle and in the smog run test, where
there is no EGR operation, to cover a bad cat you need it to open just a crack!

However, much newer cars often don't use an EGR valve anymore! SAD! I love this
cheat! way cheaper then a new cat! I ran these cheats for years and drove the cars with
the mods in place!

 

[StevieC]

A bad Cat will lead to high Hydro Carbons not high NOx. (On Cat's without an auxilary air pump)

High NOx is due to high cylinder temperature, incorrect timing, poor or no exhaust gas recirculation (where needed) and improper fuel mixture. (In later engines it can be improperly timed valve overlap because of incorrect timing chain/belt setup or cam phasers not working properly)

High Hydro Carbons is caused by a Bad Cat, improper fuel mixture, extremely worn out engine.

High C.O. is a poor fuel mixture during idle circuit and/or a bad Cat.

 

[Malo83]

Originally Posted By: Merkava_4
Originally Posted By: bullwinkle
His '85 305 has that darned electronic Quadrajet


If that's the case, then that's the source of the failure right there. I used to have a '78 Cadillac and it would never pass smog unless the carburetor was new. And it couldn't be a parts store carburetor either; it had to be custom carburetor built by a Rochester pro shop.


Sounds like [censored]. I have the E4ME electronic Qjet and she hasn't failed an inspection, everytime a smog test comes up on my 83 Silverado with the 305 she gets a thorough tune up, cap,rotor,plugs, air filters. Have you checked the timing, you won't get a true time with the distributor hooked up to the computer, disconnect the 4 wire plug to the distributor and set your base timing to 8* then reconnect the 4 wire plug, when was the last time the oxygen sensor was changed, if it's clogged you'll never get a good reading, check the PCV valve and clean or replace, change your oil and filter, I like to spray Gumout carb spray down the carburetor at high idle speed to clean out the intake passages and the carb, spray the exterior of the carb to clean it up, last and most important is take the truck out on the freeway and drive like you stole her, high speed for at least 10 miles to get everything HOT! this will also set the computer to the new readings with a new O2 sensor, ask me how I know, failed a smog test with a new O2 sensor, didn't drive it far enough for everything to marry up, took her back out and ran on the freeway, came back and she passed with flying colors

PS. I also put a bottle of GTP in the tank, just for fun

 

[sw99]

I had to run a bottle of HEAT and a couple gallons of E85 mixed with three gallons of unleaded to get my 85' K30 to pass. Really not sure what it does but it was suggested and worked like a charm.