I'm trying to get my '84 F150 300CI Auto with carburator through DEQ. It's failing the tailpipe first idle test. The report says Hydrocarbons are okay at 169 (max allowed 220) the CO is running 6.32% (max allowed 1%). Two years ago my mechanic took it through DEQ after re-building the carb, and replacing the O2 sensor.

The report says that high CO can be from
Dirty Air cleaner, Contamiated oil, Stuck Choke, Mis-adjusted Carb, Malfuctioning thermostat, Faulty catalitic converter, Malfunctioning air pump, Engine management computer failure.

I've replaced the air filter, changed the oil, checked the choke is open when warm, and replaced a badly leaking exhaust pipe. I had the muffler shop check the exhaust back pressure before the catilitic converter and it was okay, so I don't think the converter is plugged. I assume if it was okay last check that it should still be okay.

I wonder after passing the test last time the mechanic richened up the idle mixture to make it run smoother at idle and now two years later, it's DEQ time again and it won't pass. . . . and the mechanic want$ me to come vi$it him.

The truck has 89K miles on it and it's only been driven about 1200 miles since the last DEQ check 2 years ago.

Will fooling with the idle mixture help?

Thanks.

 

First thing I would do is run the computer codes. This will give you a starting point.

A plugged cat, usually makes passing an emmission test easier. Not as much emmissions going out the tailpipe etc...

It's easy to check the thermactor system. Remove the hoses from the airpump, and valves etc, and check for air coming out the pump, etc...

Adjusting the Fuel mixture could help, however, it could hinder too. It could have a bad Feedback solenoid on the carb as example, or bad O2 sensor.

Also your HC's are too high for my likeing, average is around 53 as example, although 169 is still passing it's way out of the norm, and possibly a sign of costing you fuel consumption.

Yeah, first thing I would do is a computer diagnostic.

 

Thanks for the response Guru,

I decided since I don't have any diagnostic tools, I'd just be shooting in the dark to do any further work. I took it to the mechanic and they used their tools to "adjust the carb for DEQ" They had it done in less than an hour, including taking it to DEQ and passing the test.

They said is was pretty normal for the carb needing to be adjusted. They had rebuilt the carb 2 years ago before the last test. They thought it should be good to go for a while now that the gaskets etc, have settled in.

Passed with Hydrocarbons at 150 and CO way way down at 0.1% ... amazing reduction from 6%.

So I'm good to go for at least the next 2 years. (DEQ every 2 years here in Oregon.)

 

Yeah it's the same way here in california. A bunch of BS if you ask me.

Anyway, glad it was a simple fix.