My tow rig failed emissions today in Seattle!

1983 Chevy 454 with a Quadra jet pushing a 27 ft motorhome chassis.

It failed the Carbon Monoxide at idle test.

HYDROCARBON (ppm)

Cruise Limit: 220
Cruise Emissions: 33
Idle Limit: 220
Idle Emissions: 128


CARBON MONOXIDE (%)

Cruise Limit: 1.2%
Cruise Emissions: 0.75%
Idle Limit: 1.2%
Idle Emissions: 4.78%

Unfortunately the idle mixture screws are sealed on this carburetor (for the time being). The air pump has been removed.

What is interesting is that since I replaced the heads to rectify the badly worn valve seats the HC has gone substantially down and the CO has gone substantially down.

Are the HC and CO inversely proportional?

Should I lean it out? Should I richen it up? … or should I just shoot it?


Thanks

Eddie

Carbon monoxide is the incomplete burn of carbon molecules found in fuel.

Lean it out, or maybe advance the timing just a hair. Also, make sure your spark plugs/wires/distributor cap are all in excellent working order, and it doesnt hurt to run the vehicle HARD right before the testing is done. I usually run a higher grade of fuel for the test if there's any chance of it failing.

Good luck!

Make sure aircleaner element is clean or brand new,
mike

So why is the air pump removed? The pump dilutes the exhaust stream. HC and CO can invert due to lean/rich conditions. BTW...In CA missing equipment is a fail, do not pass GO or collect 200 dollars.

Best to find a shop that will let ya play with the timing while having it on the scope. The only two other things is to drill out the adjustments on the carb and/or reinstall the air pump.

QUOTE (Brew @ Aug 9 2005, 02:43 PM)

Carbon monoxide is the incomplete burn of carbon molecules found in fuel. Lean it out, or maybe advance the timing just a hair. Also, make sure your spark plugs/wires/distributor cap are all in excellent working order, and it doesnt hurt to run the vehicle HARD right before the testing is done. I usually run a higher grade of fuel for the test if there's any chance of it failing. Good luck!

Running a HIGHER grade fuel will ensure a marginal car will fail. Higher octane fuel isn't as volatile as low octane varieties, and won't burn completely in a car not designed for its use. ANOTHER internet promulgated MYTH. Not the right thing to do. Plugs, wires, cap, and rotor will all contribute to high HCs, NOT CO. HC is unburned fuel. CO is just plain too much fuel per parts of air. Bad air filter, improperly adjusted carburetor, stuck float needle, sunken float. Very high or very low CO will result in high HCs. A good working cat will eat up a LOT od HCs, and some CO. The air pump will clean up a lot of CO, as well as some HCs. Advanced timing INCREASES HCs, and the NOX numbers suffer. Removing the air pump is a questionable practice on a vehicle that has to pass en emissions test. In states that use the California standards, missing emissions control equipment is an automatic fail, no matter how clean the tailpipe is. The Cap'n

he hit it on the nose.....

Later

Put the air pump back on...

Strictly as a function of AFR, HC and CO both fall as the mixture gets leaner. However, if you go so lean that you start to misfire at idle, HC will soar.

So, high HC, low CO means you're way too lean. High HC, high CO means you're way too rich.

NOx peaks at 14.7:1, and falls dramatically on the rich side, so for a car with no cat that has to pass a test with NOx, running just slightly rich will give best overall emissions. For a car with a cat, any failure generally means a new cat, as a functioning cat will lower emissions so much that you'll pass even fairly recent standards so long as they mixture isn't way off. If you have a car with a cat AND an O2 sensor, replace them both.

In this specific situation, it could be you've got a leaky jet in that carb somewhere adding too much fuel, so you may need to dismantle that carb and have a look. I'd pay particular attention to the idle mixture screw and it's seat, since CO is high at idle, but not at cruise.

How's your thermostat? A motorhome will have a cooling system so heavy duty that if your thermostat sticks open even a little, it'll never warm up at idle.

ERROR!

Since the head replacement, the CO went UP, not down. I'm guessing this happened since the worn valve seats reduced the actual valve lift. This is a 1983 vintage engine. I believe that it may been designed to run on leaded gas and did not have hardened valve seats. The 454 Chevy has exhaust valve rotators, and without hardened seats, some of the exhaust valve seats were erroded more than 0.175".

What is baffling is how the engine passed CO with badly worn valve seats and NO air pump ... and now with fresh heads it fails CO. Maybe the timing is too advanced.

The air pump was removed to reduce exhaust manifold temperature and manifold warping. This is a big problem with motorhomes that are used for towing due to the poor airflow in the engine compartment and the heavy load. Last time we went to Laguna Seca, the GVW (combined) was about 18,000 lbs.

I'm planning on pulling the carb and removing the idle mixture screw caps so I can get the beast through emissions and licensed befor this weekends camping trip ... when I get a spare minute ... Just need to replace the bilge pump on the boat and replace a couple of the trailer rollers before this ... and ... finish the oil cooler ducting and brake ducts on the 914/6 before next weeks track day ...

and of course ... the wife calls and says the family Suburban blew up and she's stranded with the kids!

I told her the compressor clutch was getting noisy and would soon need replacement, but when the rattling turned into screeching and white smoke starting billowing out from behind the car, she knew something was serious. Suddenly the power steering gave out and she smartly pulled to the shoulder of the off-ramp ... temp gauge was pegged too?

When I showed up and looked under the hood, I was surprised that the serpentine belt hadn't started on fire! It was fried! No amount of pounding and prying could get the compressor clutch to free up.

I sent the family home in the M5 and waited for my buddy to show up with the flatbed. Then I remembered that there was a Chevy dealer about 1/2 a mile away. I risked running with no waterpump, fan, power steering or power brakes (hydraulic boosted) and backed up the next onramp. I had my fingers crossed that the parts department was open until 6:00pm. No dice! It was 5:45 and the door to the parts department was locked and the lights were out. I caught a glimpse of a solitary sole behind the counter and rapped on the door. It was the parts manager. I pleaded with him. He very graciously opened the dooe and sold me a complete compressor. $400 ... it was ONLY money.

I unbolted the fried compressor and wired it to the fender. Bolted the new compressor in place and slipped on the spare belt. No hoses. No wires. No problem. I just needed the compressor pulley to idle. IT WORKED!

I'm home.

Thanks for all the help with the emissions.

Got to go!

Out to the garage!

Thanks!

Eddie

get a carb rebuild kit and replace the float. q-jets are bad for having the float saturate and get heavy which causes high fuel levels in the float bowl, this causes rich idle condition.

hope this helps