Failed GA emissions test. Need help.

[krisj]

Last year I moved to the Atlanta area. Metro area ATL requires passing emissions testing for vehicles under 25 years old. I lived in Tallahassee, FL for many years and there is no emissions testing there.
My truck is a '94 3/4 ton 5.7 with about 250k miles. It runs pretty well considering it's age, but failed emissions due to high HC and high NOx on both 25/25 and 50/15.
On 25/25 test HC(hydro carbon) ppm was 178. Up to 131 is allowable...FAIL, and NO(nitrogen) ppm was 2510. Up to 818 is allowable...FAIL. Everything else passed on the 25/25 test.
On the 50/15 test HC ppm was 167 / 134 allowable...FAIL, and NO ppm was 2532 / 893 allowable... FAIL. Everything else on 50/15 test passed.
Every now and then my SES light comes on. I pulled codes with a paper clip and retrieved code 32 which I think is EGR. Last year I replaced the EGR sensor and the other day my friend tested the valve and the engine choked down like it should. Plugs are whitish tan.
Does anyone know how to interpret the test data and tell me what to fix or replace? I sure could use some advice. Thanks.


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[michael hurd]

Things you can do for free: With the engine running and the air cleaner off, spray a mist of cool water from a hair spray type spray bottle into the throttle body while holding the engine above idle. This may help remove some built up carbon from the combustion chambers, valves and piston crowns. There are various chemical sprays that can also help out here, but they cost money.

Water is free. Next, if you can borrow a timing light that works, clip the pickup lead on the coil wire ( instead of #1 ) point the flashing output at the injectors with the air cleaner off, and check the injector spray pattern when the engine is running. It should be a nice conical pattern with no dripping as it sprays on the throttle plates.

If the injector spray pattern is poor, consider adding an additive to the fuel to clean them, or find another throttle body and replace it.

Pull the plugs again and do a compression test, if they are all fairly balanced, then re-install the plugs.

Change the engine oil & filter.

If it does not pass after the above, consider pulling the intake to clean the EGR passages, and check the distributor carefully for a worn gear and cracks in the magnetic pick up. If in doubt install a new distributor for $ 64.

Remove the throttle body from the engine and clean it thoroughly. Check the throttle shaft for excessive play. With the throttle body off, see if you can borrow a flexible camera system where you can scope the backside of the valves without pulling the intake off. If there is a lot of build up, with that mileage it may be time for a replacement set of cylinder heads.

If it hasn't been changed in forever, put a new oxygen sensor in it... they aren't too expensive at all. ( 12 bucks ) Next, install a new catalytic convertor. This is going to cost you a few bucks, but if the rest of the engine is in sound shape, and all systems are functioning properly, this should make it pass.

With that mileage, it probably won't hurt to put a timing chain set in it at the same time.


If you can do any / all of the above work instead of taking it to a shop you will be money ahead.

 

[great white]

Michael has the meat of it. I'm just going to cut and paste rather than type it all out:

Possible Causes of High Oxides of Nitrogen (NOx) Emissions

In order to pinpoint the cause of excessive NOx emissions, the following systems (if applicable) and possible defects will need to be checked, usually in this order:
Over-Advanced Ignition Timing

Older vehicles have ignition timing systems that are adjustable and, unfortunately, anything that is adjustable is also mal-adjustable.

Fortunately, ignition timing is usually quick and easy to check. For more details, see Ignition System Testing.
Inadequate Exhaust Gas Recirculation (EGR) Flow

Operation of the Exhaust Gas Recirculation (EGR) system should be checked completely. To do this there are three areas that the technician must check:

the EGR valve
the EGR exhaust passage(s)
the EGR control system

For more information on these procedures see Exhaust Gas Recirculation (EGR) System Testing.
Lean Air-Fuel Ratio

The technician should check to ensure that there is not an excessively lean mixture being burned. Depending on the vehicle, its fuel system, and its emissions control systems, this may involve simply looking at the VIR, measuring engine-out emission levels, and O2 sensor testing.

For detailed info regarding the diagnosis of fuel delivery systems, see Fuel System Testing.
Defective Three-Way Catalytic Converter

Your technician should test the catalyst by performing a converter efficiency test (see Catalytic Converter Testing). Note that this only applies if the vehicle is equipped with a three-way catalytic converter (some 1980-87 vehicles and all 1988 and newer vehicles have three-way catalytic converters).
Combustion Chamber Deposits

If the above possibilities have been conclusively checked and no problems found, it is reasonable to conclude that combustion chamber deposits are contributing to excessive NOx emissions. For additional information see Combustion Chamber Deposits.

Possible Causes of High Hydrocarbon (HC) Emissions

Hydrocarbons relate to unburned fuel. You may logically think that must mean that the engine is getting too much fuel. However, that is only one of many possibilities ranging from fuel problems, to electrical problems, to internal engine problems such as piston rings that can cause HC emissions to be excessive.

In order to pinpoint the cause of excessive HC emissions, the following systems (if applicable) will need to be checked, usually in the order shown below:
Lean or Rich Air-Fuel Ratio

For an engine to operate as designed, the correct ratio of fuel to air must be delivered to the cylinders. If the fuel system is delivering a leaner than ideal air-fuel ratio, it may result in lean misfire and cause high hydrocarbons. If the fuel system is too rich, it also may result in high HC but will be accompanied by high CO as well.

For more info regarding the diagnosis of fuel delivery systems, see Fuel System Testing
Inadequate Catalytic Converter Efficiency

For vehicles that are 1988 model year or newer, it is very important that the catalytic converter be operating at 90% efficiency or better. That means that the emissions that come out of the tailpipe must be no more than 10% of what goes in.

For more info regarding how to determine catalytic converter efficiency, see Catalytic Converter Testing
Induction System Problems

There are many aspects of the engine's air induction system (hoses, intake runners, intake manifold, vacuum-controlled devices) that can cause disruption in the air and fuel getting to the cylinders and result in high HC. Incorrect PCV valve/orifice flow rate can also cause similar symptoms. Leaking EGR valves also may cause excessive HC emissions.

For more info regarding how induction system problems are identified, see Induction System Testing
Poor Ignition Performance

Ignition defects including dirty spark plugs, leaking or open-circuited spark plugs or wires, or defective ignition coils can all result in a shortage of spark energy. Any shortage of spark energy may cause high HC emissions.

If the spark occurs at the wrong time, incomplete combustion and high hydrocarbons may result. Too much spark advance could be due to an incorrect adjustment or a defect in mechanical or vacuum advance mechanisms.

For more info on testing ignition systems for inadequate spark energy or incorrect spark timing, see Ignition System Testing
Uneven Output Among the Engine's Cylinders

At this stage of the diagnosis the technician should be sure that the air-fuel ratio is correct, there are no external vacuum leaks, and the ignition system is operating normally. There are still many possible causes of high hydrocarbons, most of which are either internal engine problems or tough-to-detect induction system problems such as valve deposits or a leaking EGR valve. On fuel-injected vehicles, poor fuel atomization is a common cause of HC problems.

For all of these remaining possibilities, checking for uneven power output amongst cylinders will usually help to track down the cause of the problem. For more info on testing for uneven power output, see Engine Integrity Tests

 

[454ss]

the best thing you can do at this point is move to a non-communist state that doesn't have that bs testing, problem solved.

 

[michael hurd]

the best thing you can do at this point is move to a non-communist state that doesn't have that bs testing, problem solved.

If only it were that simple... sometimes, that's just not an option for people. I would love to have rust free vehicles to work on, but that's a pipe dream in this area.

 

[great white]

If only it were that simple... sometimes, that's just not an option for people. I would love to have rust free vehicles to work on, but that's a pipe dream in this area.

A vacation, a car trailer and some Canada customs paperwork can scratch that itch.....

 

[IOWNJUNK]

the best thing you can do at this point is move to a non-communist state that doesn't have that bs testing, problem solved.

Its not the whole state, only the 5 or so counties that make up Hotlanta. Most of the cars/trucks we buy come from atlanta because its cheaper and easier to dump them when the check engine light comes on or they wont pass emissions.

 

[skylark]

I have had good success with dropping a piece of cardboard in front of the radiator and retarding the piss out of the timing to limp one through.

 

[great white]

I have had good success with dropping a piece of cardboard in front of the radiator and retarding the piss out of the timing to limp one through.

Interesting. I would think retarding the timing would bring NOx down but HC up.....

 

[michael hurd]

Retarded timing will raise exhaust temperatures compared to advanced timing.