EMISSIONS

FUEL SYSTEM
Section 3D – Emissions
Table of Contents
Exhaust Emissions Standards . . . . . . . . . . . . 3D-1 Stratified Charge . . . . . . . . . . . . . . . . . . . . . 3D-4
What Are Emissions? . . . . . . . . . . . . . . . . . 3D-1 Emissions Information . . . . . . . . . . . . . . . . . . . 3D-4
Hydrocarbons – HC . . . . . . . . . . . . . . . . . . . 3D-1 Manufacturer’s Responsibility: . . . . . . . . . 3D-4
Carbon Monoxide – CO . . . . . . . . . . . . . . .
Oxides of Nitrogen - NOx . . . . . . . . . . . . . .
3D-1
3D-2
Dealer Responsibility: . . . . . . . . . . . . . . . . .
Owner Responsibility: . . . . . . . . . . . . . . . . .
3D-5
3D-5 3
Controlling Emissions . . . . . . . . . . . . . . . . .
Stoichiometric (14.7:1) Air/Fuel Ratio . . .
3D-2
3D-2
EPA Emission Regulations: . . . . . . . . . . . .
Decal Location: . . . . . . . . . . . . . . . . . . . . . .
3D-5
3D-6
D
Outboard Hydrocarbon Emissions Replacement of Certification Label . . . . . . . . 3D-7
Reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3D-2 Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3D-7
Stratified vs Homogenized Charge . . . . . . . . 3D-3 Date Code Identification . . . . . . . . . . . . . . . 3D-7
Homogenized Charge . . . . . . . . . . . . . . . . . 3D-3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 3D-7

Exhaust Emissions Standards

Through the Environmental Protection Agency (EPA), the federal government has estab-
lished exhaust emissions standards for all new marine engines sold in the United States.
What Are Emissions?
Emissions are what comes out of the exhaust system in the exhaust gas when the engine
is running. They are formed as a result of the process of combustion or incomplete com-
bustion. To understand exhaust gas emissions, remember that both air and fuel are made
of several elements. Air contains oxygen and nitrogen among other elements; gasoline
contains mainly hydrogen and carbon. These four elements combine chemically during
combustion. If combustion were complete, the mixture of air and gasoline would result in
these emissions: water, carbon dioxide and nitrogen, which are not harmful to the environ-
ment. However, combustion is not usually complete. Also, potentially harmful gases can
be formed during and after combustion.
All marine engines must reduce the emission of certain pollutants, or potentially harmful
gases, in the exhaust to conform with levels legislated by the EPA. Emissions standards
become more stringent each year. Standards are set primarily with regard to three emis-
sions: hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).
Hydrocarbons – HC
Gasoline is a hydrocarbon fuel. The two elements of hydrogen and carbon are burned
during combustion in combination with oxygen. But they are not totally consumed. Some
pass through the combustion chamber and exit the exhaust system as unburned gases
known as hydrocarbons.
Carbon Monoxide – CO
Carbon is one of the elements that make up the fuel burned in the engine along with oxy-
gen during the combustion process. If the carbon in the gasoline could combine with
enough oxygen (one carbon atom with two oxygen atoms), it would come out of the en-
gine in the form of carbon dioxide (CO2). CO2 is a harmless gas. However, carbon often
combines with insufficient oxygen (one carbon atom with one oxygen atom). This forms
carbon monoxide, CO. Carbon monoxide is the product of incomplete combustion and
is a dangerous, potentially lethal gas.

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EMISSIONS

Oxides of Nitrogen - NOx

NOx is a slightly different byproduct of combustion. Nitrogen is one of the elements that
makes up the air going into the engine. Under extremely high temperatures it combines
with oxygen to form oxides of nitrogen (NOx). This happens in the engine’s combustion
chambers when temperatures are too high. NOx itself is not harmful, but when exposed
to sunlight it combines with unburned hydrocarbons to create the visible air pollutant
known as smog. Smog is a serious problem in California as well as many other heavily
populated areas of the United States.
Controlling Emissions
There are two principle methods of reducing emissions from a two-stroke-cycle marine
engine. The first method is to control the air/fuel ratio that goes into the combustion cham-
ber. The second is to control the time when this air/fuel mixture enters the combustion
chamber. Timing is important, to prevent any unburned mixture from escaping out of the
exhaust port.
Stoichiometric (14.7:1) Air/Fuel Ratio
In the search to control pollutants and reduce exhaust emissions, engineers have discov-
ered that they can be reduced effectively if a gasoline engine operates at an air/fuel ratio
of 14.7:1. the technical term for this ideal ratio is stoichiometric. An air/fuel ratio of 14.7:1
provides the best control of all three elements in the exhaust under almost all conditions.
The HC and CO content of the exhaust gas is influenced significantly by the air/fuel ratio.
At an air/fuel ratio leaner than 14.7:1, HC and CO levels are low, but with a ratio richer
than 14.7:1 they rise rapidly. It would seem that controlling HC and CO by themselves
might not be such a difficult task; the air/fuel ratio only needs to be kept leaner than 14.7:1.
However, there is also NOx to consider.
As the air/fuel ratio becomes leaner, combustion temperatures increase. Higher combus-
tion temperatures raise the NOx content of the exhaust. However, enrichening the air/fuel
ratio to decrease combustion temperatures or reduce NOx also increases HC and CO,
as well as lowering fuel economy. So the solution to controlling NOx - as well as HC and
CO - is to keep the air/fuel ratio as close to 14.7:1 as possible.

Outboard Hydrocarbon Emissions Reductions

8 1/3%
per Year Over 9 Model Years
120

100

80

60

40

20

0
96 97 98 99 2000 01 02 03 04 05 06 07 08

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 EMISSIONS

Stratified vs Homogenized Charge

DFI engines use a stratified charge inside the combustion chamber to aid in reducing
emissions. All other models use a homogenized charge. The difference between the two
is:
Homogenized Charge
A homogenized charge has the fuel/air particles mixed evenly throughout the cylinder.
This mixing occurs inside the carburetor venturi, reed blocks and crankcase. Additional
mixing occurs as the fuel is forced through the transfer system into the cylinder.
The homogenized charge is easy to ignite when the air/fuel ratio is approximately 14.7:1.

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EMISSIONS

Stratified Charge
A stratified charge engine only pulls air through the transfer system. The fuel required for
combustion is forced into the cylinder through an injector placed in the top of the cylinder
(head). The injector sprays a fuel/air mixture in the form of a bubble into the cylinder. Sur-
rounding this bubble is air supplied by the transfer system. As the bubble is ignited and
burns, the surrounding air provides almost complete combustion before the exhaust port
opens.
A stratified charge is hard to ignite. The fuel/air bubble is not evenly mixed at 14.7:1 and
is not easily ignited.

Emissions Information
Manufacturer’s Responsibility:
Beginning with 1998 model year engines, manufacturers of all marine propulsion engines
must determine the exhaust emission levels for each engine horsepower family and certi-
fy these engines with the United States Environmental Protection Agency (EPA). A certifi-
cation decal/emissions control information label, showing emission levels and engine
specifications directly related to emissions, must be placed on each engine at the time
of manufacture.

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 EMISSIONS

Dealer Responsibility:
When performing service on all 1998 and later outboards that carry a certification, atten-
tion must be given to any adjustments that are made that affect emission levels.
Adjustments must be kept within published factory specifications.
Replacement or repair of any emission related component must be executed in a manner
that maintains emission levels within the prescribed certification standards.
Dealers are NOT to modify the engine in any manner that would alter the horsepower or
allow emission levels to exceed their predetermined factory specifications.
Exceptions include manufacturers prescribed changes, such as that for altitude adjust-
ments. Also included would be factory authorized:
• Installation of performance style gear housings by Mercury Marine.
• Service replacement parts modified, changed or superceded by Mercury Marine.

Owner Responsibility:
The owner/operator is required to have engine maintenance performed to maintain emis-
sion levels within prescribed certification standards.
The owner/operator is NOT to modify the engine in any manner that would alter the horse-
power or allow emissions levels to exceed their predetermined factory specifications.
Single engine exceptions may be allowed with permission from the EPA for racing and
testing.
EPA Emission Regulations:
All new 1998 and later outboards manufactured by Mercury Marine are certified to the
United States Environmental Protection Agency as conforming to the requirements of the
regulations for the control of air pollution from new outboard motors. This certification is
contingent on certain adjustments being set to factory standards. For this reason, the fac-
tory procedure for servicing the product must be strictly followed and, whenever practica-
ble, the product must be returned to the original intent of the design.
The responsibilities listed above are general and in no way a complete listing of the rules
and regulations pertaining to the EPA laws on exhaust emissions for marine products. For
more detailed information on this subject, you may contact the following locations:
VIA U.S. POSTAL SERVICE:
Office of Mobile Sources
Engine Programs and Compliance Division
Engine Compliance Programs Group (6403J)
401 M St. NW
Washington, DC 20460
VIA EXPRESS or COURIER MAIL:
Office of Mobile Sources
Engine Programs and Compliance Division
Engine Compliance Programs Group (6403J)
501 3rd St. NW
Washington, DC 20001
EPA INTERNET WEB SITE:
http:/www.epa.gov/omswww

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EMISSIONS

CERTIFICATION LABEL:
The certification label must be placed on each engine at the time of manufacture and must
be replaced in the same location if damaged or removed. Shown below is a typical certifi-
cation label and is not representative of any one model. Label shown below is not to scale;
(shown at twice the normal size).
a b
Emission Control 2508 c
1998
Information cc PART # 37–855211 27
This engine conforms to 1998 Model Year Idle Speed (in gear): 550 RPM d
U.S. EPA regulations for marine SI engines.
Refer to Owners Manual Timing: Not Adjustable ECM
for required maintenance Controlled e
k Spark Plug: Champion PZFR5F-11
Family: WM9XM02.5220
Gap: .040” f

Valve Clearance (Cold) mm

j Intake: N/A Exhaust: N/A g
FEL: 100.00 GM/KW-HR

135 HP DFI h
i
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC

a - Spark Ignition (SI)

b - Cubic Centimeter
c - Model year of engine and production decal part number
d - Idle Speed (In Gear)
e - Timing specifications when adjustable
f - Recommended spark plug for best engine performance
g - Valve Clearance (Four Stroke engines only)
h - Engine Horsepower rating
i - Month of production (Boxing month will punched)
j - FEL: Represents (Mercury Marine) statement of the maximum emissions out-
put for the engine family
k - Family example
W M9X M. 02.5 2 2 0

Model Year Regulation Application Unspecified

W=1998 M=Marine 1=PWC
X=1999 2=OB
Manufacturer Displacement Technology type
Mercury Marine Liter 1=Existing
Cubic Inch 2=New

Decal Location:
Model Production Part No. Service Part No. Location on Engine
1998 Merc/Mar 2.5 L V6 37-855211 26 37-855577 26 Intake Plenum STBD
DFI (135 – 150 H.P.) Side or Flywheel Cover
1999 Merc/Mar 2.5 L V6 37-856984 13 37-856985 13 Intake Plenum STBD
DFI (135 – 150 H.P.) Side or Vapor Separator

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 EMISSIONS

Replacement of Certification Label

IMPORTANT: By federal law, it is required that all 1998 and newer Mercury Marine
outboards have a visible and legible emission certification label. If this label is mis-
sing or damaged, replacement labels can be obtained from Mercury Marine.
Removal
Remove all remaining pieces of the damaged or illegible label. Do not install new label
over the old label. Use a suitable solvent to remove any traces of the old label adhesive
from the display location.
Date Code Identification
Cut and remove a “V” notch through the month of engine manufacture before installing
the new label. The month of manufacture can be found on the old label. If the label is mis-
sing or the date code illegible, contact Mercury Marine Technical Service for assistance.

Emission Control 2508 1998

Information cc PART # 37–855211 27
This engine conforms to 1998 Model Year Idle Speed (in gear): 550 RPM
U.S. EPA regulations for marine SI engines.
Refer to Owners Manual Timing: Not Adjustable ECM
for required maintenance Controlled
Family: WM9XM03.0220 Spark Plug: Champion PZFR5F-11
Gap: .040”

Valve Clearance (Cold) mm

FEL: 100.00 GM/KW-HR Intake: N/A Exhaust: N/A

135 HP DFI
b JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC

a
a - “V” Notch
b - Month of Manufacture
Installation
Install the label on a clean surface in the original factory location.

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