T- Berry's Mobile Auto Repairs

Listed below you will find tables which you can use to give you an idea of possible causes for failed state emission tests.

CONDITION (CO)

RESULTS

TOO LEAN

POOR ENGINE POWER

0.75% OR LESS

MISFIRING @ CRUISING SPEEDS

BURNED VALVES

BURNED PISTONS

SCORED CYLINDERS

SPARK KNOCK OR PING

SLIGHTLY LEAN

HIGH GAS MILEAGE

1.2% TO 0.75%

LOW EXHAUST EMISSIONS

REDUCED ENGINE POWER

SLIGHT TENDENCY TO KNOCK OR PING

STOICHIOMETRIC

BEST ALL AROUND PERFORMANCE

SLIGHTLY RICH

MAXIMUM ENGINE POWER

1.2% TO 1.7%

HIGHER EMISSIONS

HIGHER FUEL CONSUMPTION

LOWER TENDENCY TO KNOCK OR PING

TOO RICH

POOR FUEL MILEAGE

1.7% OR HIGHER

MISFIRING

HIGH EXHAUST EMISSIONS

OIL CONTAMINATION

BLACK EXHAUST

CATALYTIC CONVERTER DAMAGE

 

 

EMISSION READINGS

 •CO = Carbon Monoxide

•CO2 = Carbon Dioxide

•HC = Hydrocarbons

•O2 = Oxygen

• NOx = Oxides of Nitrogen

LEGEND: L = LOW M = MODERATE H = HIGH

 

CO

CO2

HC

O2

NOx

POSSIBLE PROBLEMS / CONDITIONS

H

L

H

L

L

Thermostat or coolant sensor faulty - cold running engine

L

H

L

L

H

Thermostat or coolant sensor faulty - hot running engine - EGR problem

L

L

L

H

L

Exhaust leak after catalytic converter

L

H

L

H

M

Injector misfire, catalytic converter operating efficiently

H

H

H

H

H

Combination of rich mixture and vacuum leak

Air-fuel ratio too rich:

H

L

LM

L

L

Rich fuel mixture

H

L

LM

L

L

Leaking fuel injectors

H

L

LM

L

L

Incorrect carburetor adjustment

H

L

LM

L

L

Power valve leaking

H

L

LM

L

L

Choke operating rich

H

L

LM

L

L

Float level too high

H

L

LM

L

L

Air filter dirty

H

L

LM

L

L

EVAP canister purge system fault

H

L

LM

L

L

PCV system problem

H

L

LM

L

L

Engine control computer malfunctioning

H

L

LM

L

L

Crankcase contaminated with raw fuel

MH

L

LM

L

H

All of the above w/catalytic converter operating efficiently

H

L

H

H

L

Rich mixture with ignition misfire

Air-fuel ratio too lean:

L

L

H

H

H

Lean fuel mixture

L

L

H

H

H

Ignition misfire

L

L

H

H

H

Vacuum leaks/air leaks between airflow sensor and throttle body

L

L

H

H

H

EGR bad or vacuum hoses misrouted

L

L

H

H

H

Carburetor settings incorrect

L

L

H

H

H

Fuel injector bad

L

L

H

H

H

O2 sensor bad or failing

L

L

H

H

H

Engine control computer malfunctioning

L

L

H

H

H

Float level too low

Major engine fault

LM

L

LM

L

LM

Compression low

LM

L

LM

L

LM

Insufficient camshaft lobe lift

LM

L

LM

L

H

Ignition timing over advanced

LM

L

LM

L

H

Spark plug wire open or grounded

LM

L

LM

L

MH

Engine control computer compensating for a vacuum leak

L

H

L

L

L

Good combustion efficiency and catalytic converter action

 


 

• When do I change my oil

• Freon changeover

• Oxygen Sensors

• Wiring Diagrams 

• TSB's and Recalls

• OBD II CODES

• NOx FAILURES

• Timing Belts_ 1970-1997 Domestic & Imported Cars

• Brake Squeals

• Certifications

 

Please feel free to contact me at the following address:

 E-mail: stberry@netzero.net

 

 

Last Updated on 4/20/2006
by Scott Throneberry
Email
:
stberry@netzero.net