Smog failure with 85 feedback carb 350

[JohnKimble]

Hello,

Went to smog the 85 k10 today and failed. The HC and CO limits were so high it was in the gross pollution threshold. The engine is stock with all smog equipment still hooked up and running. Recently did the cap, rotor, wires, plugs and oil. Air filter is good.

The smog guys were surprised because of how well the truck runs and how terribly it failed. The only thing I could think of was that I had the battery unplugged and charging since the truck has been garaged for the last 6 months. I filled it with premium on my way to the smog shop and ran it warm to heat up the cat.

Could it be the 10 mile and 20 minute distance wasn't enough for the computer to calibrate the feedback carb, or is that not how it works?

[Ziegelsteinfaust]

A few things to consider first. Drive it for about an hour at freeway speeds with 87. Low compression engines run better with it. Change the oil, and get it smogged again.

If that doesn't work it maybe a carb issue.

Options if the price is to high to bother with.

Get a 75 and earlier title. GM only told you what weight class your truck was, and rather 2 or 4wd. I am going to have a pre smog crew this way around Christmas.

Or you could spring for a 6.2 erod swap. It is pricey compared to a 5.3 swap, but it is guaranteed to pass by design. Meaning if you hook it up to your existing vapor stuff your good. Where as the 5.3 you have to move everything over. People have done it, but it takes a lot of leg work.

[Matt Man]

High hydrocarbons and CO is a sign of the fuel mixture being too rich. Does the truck get up to the correct operating temperature? You can check with a thermal laser gun if you don't trust the gauge. I think the feedback carbs are supposed to adjust the fuel mixture by themselves with the electronic solenoids on top right? I would pull a spark plug and look a the condition of it. Also, I am not 100% sure but I think the %CO2 category on the smog check sheet is the fuel air ratio being measured. Yours is below 10 and is supposed to be around 14:7 in a perfect world.

Here is the California smog website where it will tell you what causes certain conditions. https://www.smogtips.com/failed-high...onoxide-CO.cfm

[donw1986]

I ditched my feedback carb on my 86 for the msd efi throttle body injection i live in calif tough smog laws here, and it passed with flying colors, it runs way better that that stupid carb i have alway had problems with that thing

[JohnKimble]

My whole goal here is just to pass smog so I can sell it. Don't want to put much money into it at all.

I have a 75 that will take my money.

Does anyone know if this feedback carb actually takes xx miles after resetting the battery for the ecm to change its fuel ratio/etc or is it immediate?

[JohnKimble]

Quick question. When I did the distributor cap I went with the AC Delco D336X.

I see on rock auto one distributor cap labeled "California" called DC800X.

Is the distributor cap a smog specific part? Possibly the one I put in their is missing something the California compatible cap has?

[KrazyRay]

Run the 87 octane.
Put some Lucas Oil fuel injector cleaner in your gas tank.
Run it hot going up and down the freeway.
Go to the smog shop and hope for the best.

Plan B: Get your tank almost empty and throw a couple gallons of white gas in the tank and take it to the smog shop. Fill up with 87 right after leaving the smog shop.

Plan C: Sell the truck on ebay to an out of state buyer who is not subject to California smog inspections.

[JohnKimble]

Small update. I pulled codes and I am getting a code 41: No distributor reference signal. Any ideas?

[Matt Man]

maybe this will help: https://repairpal.com/gm-obd-code-41

[Mr_Rich]

I'm surprised no one mentioned this, but maybe it's not common for most. Check your mixture control solenoid. Remove it from the carb and inspect it. It could very well be broken on the end where the O-ring exists which is causing the rich mixture. I took a class at the local JC too many years ago to admit, but I owned an '86 Jeep Comanche shortly afterwards that had the feedback carb and that problem was discussed.
And with that code 41 I'd use a dial-back-to-zero timing light to check *total* timing and not just static timing. Maybe that module went bad.

[57NAPCO]

For this very reason you can pick up some pretty good deals in California. It sucks for those who live there but good for us looking for square body trucks.

BTW, born and raised in the Bay Area.