Help with Smog failure

[bmort]

Hello everyone, I am trying to get an inherited 1988 Silverado 2500 up and running. It is failing the smog test for HC @ 15mph. Measuring 125 where max is 100. Passes the HC @ 25 mph. It also failed the Fuel Evaporative Control Function check. There are no error codes. Being a ODB 1, I have purchased the ALDL scan cable from Red Devil River as suggested on the board. My question is, once I have it plugged in and running, what should I be looking for in the TunerRT dashboard to tell me what I need to replace? If the oxygen sensor was bad, or the CAT needs replacement, what should I be looking for?

Thank you for any input!

 

[studigggs]

I would start with a tune up. New OEM plugs, wires, cap, rotor, fresh oil and filter. If it hasn't been done in 30k miles or so, get a TBI rebuild kit and spend an afternoon cleaning and replacing gaskets and o-rings. Carb cleaner on the butterfly and IAC passages. Before you go to the smog station, put some good fuel in it from tier-1 station, take it for a 30 minute drive to get it nice and hot before they pull it in. This has worked for me over the last 15 years. I failed my first smog when I brought my '90 to California. The above process has worked since.

 

[L31MaxExpress]

Probably a vacuum leak in the evap system. Look over the hoses and connections or have the system smoke tested.

Plugs, cap, rotor, wires and PCV valve. Run the tank down fairly low, about 1/4 tank and put a gallon of denatured alcohol in it. Get it up to temp and make sure its left running prior to the test. The alcohol burns cleaner and will drastically cut HCs.

 

[bmort]

I should have mentioned it got a tune up as soon as I got it, also had the fuel pump and fuel filter replaced. Manifold gasket was replaced. New thermostat.

 

[bmort]

Probably a vacuum leak in the evap system. Look over the hoses and connections or have the system smoke tested.

Plugs, cap, rotor, wires and PCV valve. Run the tank down fairly low, about 1/4 tank and put a gallon of denatured alcohol in it. Get it up to temp and make sure its left running prior to the test. The alcohol burns cleaner and will drastically cut HCs.

I had been told to run 87 as it burns cleaner. If I were to add denatured alcohol, would you recommend I fill the rest up with regular or Premium?

 

[L31MaxExpress]

I had been told to run 87 as it burns cleaner. If I were to add denatured alcohol, would you recommend I fill the rest up with regular or Premium?

Premium burns cleanest. Slower, longer burn.

 

[Schurkey]

I am trying to get an inherited 1988 Silverado 2500 up and running. It is failing the smog test for HC @ 15mph. Measuring 125 where max is 100. Passes the HC @ 25 mph.

What are the rest of the emissions test results?

High HC, low CO = misfire

High HC, high CO = rich mixture

Use a non-contact (infrared) thermometer to check the catalytic converter inlet vs. outlet temperature after the truck has FULLY warmed-up. After a 20+ mile drive, for example. The outlet better be hotter than the inlet. Wouldn't surprise me to find that the engine is running fine, but the catalyst is ancient and defective.

How old is the O2 sensor? They don't last forever. Unlike most of the other sensors, O2 sensors have a limited service life. A coolant temp sensor may last the life of the vehicle, an O2 sensor begins wearing-out the day it's installed. Any O2 sensor over 50K miles is suspect. Over 100K miles, they're a good candidate for replacement. They get "lazy"--slow to respond as they age.

It also failed the Fuel Evaporative Control Function check.

This vehicle doesn't self-test the Evap system. HOW are they testing it?

At minimum, maybe you need a new gas-cap. Maybe the charcoal canister has failed. Maybe a broken hose. No way to know until each system is verified; and it'd be a help to know how they determined it was faulty.

 

[GoToGuy]

I agree with Schurkey if you don't know how old the O2 sensor is, they get lazy slow to respond, affects mixture. When changing use an NGK/NTK, better reponse with OBD 1 systems. Some other brands new O2 sensors can cause false high HC on smog test.

 

[bmort]

What are the rest of the emissions test results?

You must be registered for see images attach

CO is within passing range, but higher than average.

Not sure when the o2 sensor was replaced last, will add that to my list. Thank you for the info on the cat, I will measure those temps soon.

 

[studigggs]

This vehicle doesn't self-test the Evap system. HOW are they testing it?

Believe they clamp the hose from the carbon canister to the gas tank then pressurize the tank via a gas cap adapter.