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Failed Smog Check 1981 Trans AM



 
 
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Old January 30th 05, 05:16 PM
TheSmogTech
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Default Failed Smog Check 1981 Trans AM

THIS VIR REPORT COMPLIMENTS OF WWW.SMOGTIPS.COM. 1981 PONTIAC TRANS AM
4.9 LITER ENGINE. SMOGTIPS SMOGSMART REPORT #1121236. Your vehicle
appears to be running rich and causing a rich misfire. Your vehicle
produced high CO at 15/25mph with high HC at 15/25 mph. Possible rich
mixture. Potential ignition concerns. Vehicle failed CO with very high
numbers. This condition is called a "rich fuel mixture". CO levels of
this amount in most cases automatically produce high HC. The condition
which causes the high HC (due to high CO) is called a "Rich Misfire".
The diagnosis for this failure should include close inspection of your
vehicle's fuel management and control systems, with heavy emphasis on
the carburetor. The engine ignition system must also be diagnosed. HC
faults (if not related to fuel mixture problems) are most often due to
improper fuel ignition.

Some Specifics: Possible vehicle hesitation. From the numbers on the
VIR report it's apparent that your vehicle is experiencing some sort of
engine trouble. More then likely this is the same trouble causing your
vehicle to fail the smog test.

How a Rich Misfire causes high CO: CO stands for Carbon Monoxide. It is
a by-product of incomplete combustion, more then often related to the
presentation of too much fuel to the combustion chambers. The spark
created at the sparkplug can only burn a small amount of fuel, the fuel
it cannot burn is sent out the tailpipe and will normally contain high
levels of partially burned fuel(CO) and un-burned fuel(HC). Let's look
at two primary causes for excessive fuel presentation to the combustion
chambers.Fuel distribution to your engine's combustion chambers is
primarily controlled by the carburetor. If any component within the
carburetor is defective air/fuel ratio can be disrupted and result in
incomplete combustion. The presentation of too much fuel will produce
high CO emissions. The presentation of not enough fuel will produce low
CO emissions. If your engine's carburetor is defective you have two
options. You can ask a local smog tech to try and adjust the carburetor
(if possible) or you can ask to have the carburetor rebuilt (a little
more expensive but the performance increase will definitely be
noticeable).

Fuel distribution is also controlled by your vehicle's computer system.
Your engine has a component called the Oxygen Sensor which is
responsible for letting the computer know how much fuel is in the
exhaust system as it exits the engine. This allows the computer to
determine how much fuel it should continue to deliver to the combustion
chambers in order to meet the proper Air/Fuel ratio. If for any reason
the 02 sensor (oxygen sensor) does not send accurate information to the
computer, the fuel delivery program may be altered. The computer will
then present either too much or not enough fuel to the combustion
chambers and cause an emission failure.

I also recommend you look into the rest of the fuel management
components. In a computer controlled engine such as this, there are
several components which also play a role in determining Air/Fuel
ratio. Along with the Oxygen Sensor, components such as the, TPS
(Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and
the MAP (Manifold Absolute Pressure Sensor) sensors also send vital
engine information to the computer which is used to determine proper
air to fuel ratio.

Now, coming back to the carburetor. The carburetor has within it, an
electromagnetic control, usually a Fuel Mixture Solenoid, which
determine your engine fuel to air mixture. This component may be at
fault. However, keep in mind "this component" only works when supplied
information from the emissions control system (mainly, the oxygen
sensor). So with this said, I recommend a smog technician perform a
feedback test to insure the oxygen sensor is in proper communication
with the fuel control system.

What does HC have to do with the High CO: HC otherwise known as
Hydrocarbon, is basically raw fuel (Gasoline). In your vehicle's
engine, "gasoline" is combined with air. The mixture is then given an
electrical spark through the spark plug to create an enormous
explosion. The by-product of this chemical reaction should
theoretically be water and heat, which is really steam(exhaust).
Normally however, we end up with a little amount of unburned(HC) and
partially burned fuel(CO), and this is were we get our HC and CO
readings. The more efficiently your engine runs, in other words, the
more fuel it burns in every combustion stroke the less HC & CO will be
emitted from the tailpipe. So the goal is to keep the engine burning
fuel as thoroughly as possible. Keep in mind your vehicle will always
emit some HC. However the goal is to keep it as low as possible.

There is a condition called the "Rich Misfire" which causes high HC and
is due to high CO. A Rich Misfire is created when, for any reason, the
combustion chambers receive too much fuel, causing the fuel that is
delivered to burn improperly and leave behind high levels of raw
fuel(HC) and partially burned fuel(CO). As mentioned, fuel distribution
to your engine's combustion chambers is controlled by your vehicle's
ECU(Engine Control Unit) and carburetor.

However keep in mind, if fuel management is not the reason for your
vehicle's HC failure, the problem might be engine ignition related. Out
of the three main systems your engine relies on to produce power... the
air intake system, the fuel distribution system and the spark control
system, the Spark system has the highest likelihood of becoming
defective sooner then the first two systems because of the fact that
the spark system (I.e.. Sparkplugs, Spark Plug Wires, Rotor & Cap) are
constantly exposed to high temperatures and high voltages and wear out
sooner. A defective spark system will cause your engine to burn fuel
improperly leaving behind high levels of HC. You must also insure your
engine's ignition system is functioning properly, by inspecting all the
sparkplugs and their wires. If any of the plugs look worn out or have
excessive carbon build-up replace them immediately. You may use any
brand of product designed to work in your vehicle. Most of the time
aftermarket parts (non-factory) will be much cheaper.

Final Comment: There will be a few steps involved in finding out the
root cause for your vehicle's failure/s. You should consider now this
will take some time and money. The emissions system/s responsible for
causing high CO & HC will have to be individually diagnosed, and
step-by-step eliminated as faults. Please Remember: California law only
allows State Certified Smog Repair stations to conduct smog inspections
and smog repairs on vehicles being driven in California. We highly
recommend you search our database of SmogTips State Certified Smog
Repairs stations. SmogTips Certified Stations are pre-screened for
quality repairs, fast friendly service, and reasonable prices.

SMOGTIPS SMOGSMART VIR REPORTS - Save Money. Smog Smart. SmogTips.com -
"California's Leading Smog Check Support Group" - 1-877-SMOG-TIPS



Michael Dash wrote:
> I have a 1981 Pontiac Trans Am Turbo 4.9 liter. I recently failed a

Smog
> Check, in one area: Hydrocarbons at 25 mph (max is 96, they measured

119).
> The place that tested it was a "Test Only" facility, so I took the

care to
> Pep Boys to have th problem diagnosed. They indicated I had a

problem with
> some of my spark plug wires and "recommended" a tune-up. I found the

spark
> plug wire diagnosis believable due to the fact that some of the wires

run
> close to the turbo and can be damaged. I told Pep Boys to replace the

spark
> plug wires only and see if that gets my car to pass. When they

finished
> they told me my car passed. They got my car to pass by 2 points (max

is
> 96, they measured 94). I was concerned that passing my car by what
> appeared to be a slim margin was not a sign that they solved the

problem.
> Pep Boys assured me they solved the problem and that I would pass my
> retest. So, I went back to the original test facility to get my

free
> retest, and I failed worse than the original test (max is 96, they

measured
> 135).
>
> I went back to Pep Boys to tell them I that I wanted to check my car

again
> (no charge) and figure out what the real problem is. I got the

strong
> impression that the Pep Boys Service writer was trying to place the

blame
> on the Test Center and the fact that I didn't get the tune-up. The

reason
> I didn't get the tune-up is (a) Pep Boys has a habit of recommending
> tune-ups whether you need them or not, and (b) I don't believe this

will
> solve the problem. If the problem was the need for a tune-up, I

suspect I
> would have failed HC emissions for 15 mph as well. I spoke to a

friend of
> mine (he's a mechanic in Denver, I live in the LA area) and he said

the
> numbers didn't make him suspect the ignition system, but the

evaporative
> system (charcoal canister), since the problem appears to be RPM

related.
>
> I guess what my question is to the group is, given my test results,

what is
> the diagnostic check list to perform. My concern is that many

mechanics,
> in my experience, don't truly diagnose a car, they guess. They

recommend
> various repairs until the problem resolves itself (i.e. tune-ups).

This
> results in performing unnecessary repairs as a diagnostic tool. I

don't
> wan to do this. I would like to find an official (i.e. Bureau of
> Automotive Repair, Mechanics Association, etc.) checklist for what a
> mechanic is supposed to check when diagnosing my particular problem

with HC
> emissions. I appreciate any information. Please e-mail as I do not

read
> this newsgroup often.
>
>
> Note: Below are the actual test results and information on relevant
> repairs I've made for my car. Thanks.
>
> Mike
>
>
>
>
> First Smog Check 2/20/99:
> =========================
> 15 mph (1390 RPM) | 25 mph ( 998 RPM)
> ------------------------------------------------------------------
> | maximum | average | measured | maximum | average | measured |
> ------------------------------------------------------------------
> HC | 162 | 52 | 155 | 96 | 32 | 119 |
> ------------------------------------------------------------------
> CO | 0.91 | 0.20 | 0.50 | 0.71 | 0.14 | 0.51 |
> ------------------------------------------------------------------
> NO | 2164 | 475 | 1110 | 1964 | 499 | 759 |
> ------------------------------------------------------------------
> CO2| 13.7% | 13.6% |
> ------------------------------------------------------------------
> O2 | 0.9% | 1.0% |
> ------------------------------------------------------------------
>
>
>
> Smog Test by Pep Boys 2/22/99: (Spark Plug Wires replaced)
> ================================================== ========
> 15 mph (1394 RPM) | 25 mph (1021 RPM)
> ------------------------------------------------------------------
> | maximum | average | measured | maximum | average | measured |
> ------------------------------------------------------------------
> HC | 162 | 52 | 87 | 96 | 32 | 94 |
> ------------------------------------------------------------------
> CO | 0.91 | 0.20 | 0.50 | 0.71 | 0.14 | 0.58 |
> ------------------------------------------------------------------
> NO | 2164 | 475 | 1112 | 1964 | 499 | 959 |
> ------------------------------------------------------------------
> CO2| 13.8% | 13.4% |
> ------------------------------------------------------------------
> O2 | 1.0% | 1.5% |
> ------------------------------------------------------------------
>
>
>
> Smog Check (Restest) 2/27/99
>
> 15 mph (1415 RPM) | 25 mph (1642 RPM)
> ------------------------------------------------------------------
> | maximum | average | measured | maximum | average | measured |
> ------------------------------------------------------------------
> HC | 162 | 52 | 124 | 96 | 32 | 135 |
> ------------------------------------------------------------------
> CO | 0.91 | 0.20 | 0.50 | 0.71 | 0.14 | 0.58 |
> ------------------------------------------------------------------
> NO | 2164 | 475 | 1621 | 1964 | 499 | 1772 |
> ------------------------------------------------------------------
> CO2| 13.8% | 13.7% |
> ------------------------------------------------------------------
> O2 | 0.7% | 0.6% |
> ------------------------------------------------------------------
>
>
> Relevant repairs:
> =================
>
> Mileage | Date | Repair
> ----------------------------------------------------------------
> 88,734 | 12/22/92 | Rebuild Carburetor
> ----------------------------------------------------------------
> 107,061 | 01/02/96 | Replace catalytic converter
> | | and mufflers
> ----------------------------------------------------------------
> 110,712 | 10/24/96 | Replace Distributer, Cap/Rotor.
> | | Ignition module, pickup coil
> ----------------------------------------------------------------
> 112,433 | 03/25/97 | Replace spark plug wires (NAPA)
> | | and spark plugs (AC/Delco Rapid Fire)
> ----------------------------------------------------------------
> 116,947 | 05/06/98 | Replace PCV valve and hose
> ----------------------------------------------------------------
> 119,366 | 02/23/99 | Replace spark plug wires (Pep Boys)
> ----------------------------------------------------------------
>
>
> Michael Dash
>
>
> Remove ".no-spam" from my return address to reply to me by e-mail
>
> ************************************************** ******************
> *The above statements represent my personal opinion and are not *
> *necessarily the opinion of any other individual or organization. *
> ************************************************** ******************


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