Woodward GECO User manual

Technical Manual 03554
(Revision D)
Original Instructions
GECO™& GECO Vista
Stoichiometric Gas Engine Controls
Air/Fuel Ratio Control
for Emissions-controlled, Stationary Gas Engines
Installation and Operation Manual

DEFINITIONS
This is the safety alert symbol. It is used to alert you to potential personal
injury hazards. Obey all safety messages that follow this symbol to avoid
possible injury or death.
DANGER—Indicates a hazardous situation which, if not avoided, will result in death
or serious injury.
WARNING—Indicates a hazardous situation which, if not avoided, could result in
death or serious injury.
CAUTION—Indicates a hazardous situation which, if not avoided, could result in
minor or moderate injury.
NOTICE—Indicates a hazard that could result in property damage only (including
damage to the control).
IMPORTANT—Designates an operating tip or maintenance suggestion.
The engine, turbine, or other type of prime mover should be equipped with an
overspeed shutdown device to protect against runaway or damage to the prime
mover with possible personal injury, loss of life, or property damage.
The overspeed shutdown device must be totally independent of the prime mover
control system. An overtemperature or overpressure shutdown device may also
be needed for safety, as appropriate.
Read this entire manual and all other publications pertaining to the work to be performed before
installing, operating, or servicing this equipment. Practice all plant and safety instructions and
precautions. Failure to follow instructions can cause personal injury and/or property damage.
This publication may have been revised or updated since this copy was produced. To verify that
you have the latest revision, be sure to check the publications page on the Woodward website:
www.woodward.com/searchpublications.aspx
The current revision and distribution restriction of all publications are shown in manual 26311.
The latest version of most publications is available on the publications page. If your publication is
not there, please contact your customer service representative to get the latest copy.
Any unauthorized modifications to or use of this equipment outside its specified mechanical,
electrical, or other operating limits may cause personal injury and/or property damage, including
damage to the equipment. Any such unauthorized modifications: (i) constitute "misuse" and/or
"negligence" within the meaning of the product warranty thereby excluding warranty coverage
for any resulting damage, and (ii) invalidate product certifications or listings.
To prevent damage to a control system that uses an alternator or battery-charging
device, make sure the charging device is turned off before disconnecting the battery
from the system.
To prevent damage to electronic components caused by improper handling, read
and observe the precautions in Woodward manual 82715, Guide for Handling and
Protection of Electronic Controls, Printed Circuit Boards, and Modules.
Revisions—Text changes are indicated by a black line alongside the text.
Woodward reserves the right to update any portion of this publication at any time. Information provided by Woodward is
believed to be correct and reliable. However, no responsibility is assumed by Woodward unless otherwise expressly
undertaken.
© Woodward 1997
All Rights Reserved

Manual 03554 GECOStoichiometric
Woodward i
Contents
REGULATORY COMPLIANCE ....................................................................... IV
ELECTROSTATIC DISCHARGE AWARENESS ..................................................V
CHAPTER 1. GENERAL INFORMATION...........................................................1
Welcome!................................................................................................................1 
GECOStoichiometric System Features.................................................................1 
Definitions of Terms and Abbreviations..................................................................2 
GECOStoichiometric Control Specifications .........................................................3 
Environmental Specifications .................................................................................4 
Tecknocraft Trim Valve Environmental Specifications ...........................................4 
L-Series Trim Valve Environmental Specifications ................................................4 
CHAPTER 2. SYSTEM DESCRIPTION AND APPLICATION.................................5
GECO™Stoichiometric Air/Fuel Ratio Control ......................................................5 
Pre-Catalyst Exhaust Oxygen Control....................................................................6 
Post-Catalyst Exhaust Oxygen Control ..................................................................6 
EGO3 Offset ...........................................................................................................7 
Open Loop Control Mode .......................................................................................8 
Valve-Learn Function .............................................................................................8 
Fuel Valve Dithering ...............................................................................................9 
Diagnostics and Monitoring ....................................................................................9 
Communications.....................................................................................................9 
Modbus Communication.......................................................................................10 
System Diagram Examples ..................................................................................11 
CHAPTER 3. SYSTEM COMPONENTS ..........................................................13
Circuit Board Panel Assembly..............................................................................13 
Hand-Held Terminal .............................................................................................14 
Enclosure..............................................................................................................14 
Fuel Control Valve for Supplementary Applications.............................................16 
Fuel Control Valve for Full-flow Applications........................................................18 
Exhaust Gas Oxygen (EGO) Sensor....................................................................19 
Heated Exhaust Gas Oxygen (HEGO) Sensor ....................................................19 
MAP Sensor .........................................................................................................20 
PC Service Tool Software ....................................................................................21 
Status Indicator LEDs...........................................................................................21 
LED Wiring Diagram.............................................................................................22 
CHAPTER 4. CONTROL OPERATION ...........................................................23
Closed Loop Strategy ...........................................................................................23 
Open Loop Strategy .............................................................................................25 
Start-up Strategy ..................................................................................................25 
Modbus Communication.......................................................................................26 
CHAPTER 5. HAND-HELD TERMINAL OPERATION .......................................28
Hand-Held Terminal Operation ............................................................................28 
Hand-Held Navigation and Control Keys..............................................................28 
Hand-Held Terminal Control Screens ..................................................................29 
Hand-Held Terminal Configuration Screens.........................................................31 
Hand-Held Programmer Configuration.................................................................32 
CHAPTER 6. PC INTERFACE SOFTWARE OPERATION..................................33
Introduction...........................................................................................................33 
Screen Navigation ................................................................................................33 
Plotting and Data Logging ....................................................................................45 

GECOStoichiometric Manual 03554
ii Woodward
Contents
CHAPTER 7. GECO™ VISTA HMI DISPLAY ................................................46
Overview...............................................................................................................46 
Navigation.............................................................................................................46 
Main Screen..........................................................................................................47 
Alarm Screen ........................................................................................................48 
Trend Screen ........................................................................................................48 
Diagnostic Screen ................................................................................................49 
HMI Display Offline Mode.....................................................................................49 
HMI Screen Brightness Adjustment......................................................................51 
CHAPTER 8. INSTALLATION/SETUP.............................................................52
Installation Tasks ..................................................................................................52 
Included GECOStoichiometric Components .......................................................52 
Optional GECOStoichiometric Components .......................................................52 
Required Installer-Provided Components ............................................................53 
Optional Installer-Supplied Components..............................................................53 
Unpacking.............................................................................................................53 
Power Requirements ............................................................................................53 
Control Location Considerations ..........................................................................54 
Class I, Division 2, Groups A, B, C, D Hazardous Locations ...............................55 
Wiring Installation .................................................................................................55 
Making Electrical Connections .............................................................................55 
Status Indicator LEDs...........................................................................................62 
Software Installation .............................................................................................62 
Updating Application Programming (.S19 file) .....................................................63 
Fuel Metering/Valve Location Considerations......................................................63 
Plumbing Considerations......................................................................................63 
EGO Installation....................................................................................................64 
HEGO Installation .................................................................................................65 
Catalyst Temperature Sensor Installation ............................................................65 
Supplemental Valve Installation Diagrams...........................................................66 
Full-flow Valve Installation Diagrams....................................................................67 
Configuration and Calibration ...............................................................................68 
CHAPTER 9. MAINTENANCE AND FAULT INDICATIONS .................................70
Maintenance .........................................................................................................70 
Safety Checks.......................................................................................................70 
Replacement Information .....................................................................................70 
Troubleshooting ....................................................................................................71 
Recommended Spare Parts .................................................................................73 
CHAPTER 10. SERVICE OPTIONS................................................................74
Product Service Options.......................................................................................74 
Woodward Factory Servicing Options ..................................................................75 
Returning Equipment for Repair ...........................................................................75 
Replacement Parts ...............................................................................................76 
Engineering Services............................................................................................76 
How to Contact Woodward...................................................................................77 
Technical Assistance ............................................................................................77 
APPENDIX.MODBUS REGISTER ADDRESSES ..............................................78

Manual 03554 GECOStoichiometric
Woodward iii
Illustrations and Tables
Figure 2-1. System Components............................................................................5

Figure 2-2. Pre-Catalyst Emissions........................................................................6 
Figure 2-3. Post-Catalyst Emissions ......................................................................6 
Figure 2-4. Basic Control Logic for Pre-catalyst EGO Control ...............................6 
Figure 2-5. Basic Control Logic for Post-catalyst EGO Control .............................7 
Figure 2-6. Control Logic with EGO3 Offset...........................................................7 
Figure 2-7. Control Logic for Open Loop Control ...................................................8 
Figure 2-8. Control Logic for Valve-Learn Function ...............................................9 
Figure 2-9. PC Communications ..........................................................................10 
Figure 2-10. PC Software Tool Display Screen Example ....................................10 
Figure 2-11. GECO System for Single Carburetor Engine...................................11 
Figure 2-12. GECO System for Dual Carburetor Engine .....................................12 
Figure 3-1. Mounting Dimensions ........................................................................15 
Figure 3-2. Circuit Board Cover (wiring legend plate) ..........................................16 
Figure 3-3. Valve Outline Drawing .......................................................................17 
Figure 3-4. HEGO Sensor Connector Pin Arrangement ......................................20 
Figure 4-1. Pre-Catalyst EGO Closed Loop Control Mode Diagram ...................23 
Figure 4-2. Adaptive EGO Closed Loop Control Mode Diagram .........................24 
Figure 4-3. Open Loop Control Mode Diagram....................................................25 
Figure 4-4. Start Sequence Flowchart..................................................................26 
Figure 7-1. GECO Vista HMI Screen Navigation .................................................46 
Figure 7-2. GECO Vista HMI Splash Screen .......................................................46 
Figure 7-3. GECO Vista Main Screen ..................................................................47 
Figure 7-4. GECO Vista V-Bank Main Screen .....................................................47 
Figure 7-5. GECO Vista Alarm Screen.................................................................48 
Figure 7-6. GECO Vista Trend Screen.................................................................48 
Figure 7-7. GECO Vista Diagnostic Screen .........................................................49 
Figure 8-1. Enclosure Outline Drawing ................................................................54 
Figure 8-2. Wiring for Single Bank .......................................................................58 
Figure 8-3. Wiring for Dual Bank ..........................................................................60 
Figure 8-4. Legend Plate......................................................................................61 
Figure 8-5. Valve Outline Drawing .......................................................................66 
Figure 8-6. L-Series ITB Outline Drawings...........................................................67 

GECOStoichiometric Manual 03554
iv Woodward
Regulatory Compliance
North American Compliance:
These listings are limited only to GECO™ Stoichiometric models with CSA
marking.
CSA: CSA Certified for Class I, Division 2, Groups A, B, C, & D, T5
at 70 °C Ambient. For use in Canada and the United States.
Certificate 1214651
These listings are limited only to GECO Vista models with CSA marking.
CSA: CSA Certified for Class I, Division 2, Groups A, B, C, & D,
T4A at 40 °C Ambient. For use in Canada and the United
States.
Certificate 1214651
Special Conditions for Safe Use:
The open-type units are certified as components to be used within a suitable
enclosure. The final assembly is subject to acceptance by the authority having
jurisdiction.
Wiring must be in accordance with North American Class I, Division 2 wiring
methods as applicable, and in accordance with the authority having jurisdiction.
On GECO Vista models, input power must be supplied from an NEC or CEC
class 2 power source.
EXPLOSION HAZARD—Do not disconnect equipment while circuit is
live unless the area is known to be non-hazardous.
Substitution of components may impair suitability for Class I,
Division 2.
RISQUE D’EXPLOSION—Ne pas débrancher l'équipement
tant que l'installation est sous tension, sauf en cas
l’ambiance est décidément non dangereuse.
La substitution de composants peut rendre ce matériel
inacceptable pour les emplacements de Classe I, Division 2.

Manual 03554 GECOStoichiometric
Woodward v
Electrostatic Discharge Awareness
All electronic equipment is static-sensitive, some components more than others.
To protect these components from static damage, you must take special
precautions to minimize or eliminate electrostatic discharges.
Follow these precautions when working with or near the control.
1. Before doing maintenance on the electronic control, discharge the static
electricity on your body to ground by touching and holding a grounded metal
object (pipes, cabinets, equipment, etc.).
2. Avoid the build-up of static electricity on your body by not wearing clothing
made of synthetic materials. Wear cotton or cotton-blend materials as much
as possible because these do not store static electric charges as much as
synthetics.
3. Keep plastic, vinyl, and Styrofoam materials (such as plastic or Styrofoam
cups, cup holders, cigarette packages, cellophane wrappers, vinyl books or
folders, plastic bottles, and plastic ash trays) away from the control, the
modules, and the work area as much as possible.
4. Do not remove the printed circuit board (PCB) from the control cabinet
unless absolutely necessary. If you must remove the PCB from the control
cabinet, follow these precautions:
Do not touch any part of the PCB except the edges.
Do not touch the electrical conductors, the connectors, or the
components with conductive devices or with your hands.
When replacing a PCB, keep the new PCB in the plastic antistatic
protective bag it comes in until you are ready to install it. Immediately
after removing the old PCB from the control cabinet, place it in the
antistatic protective bag.
To prevent damage to electronic components caused by improper
handling, read and observe the precautions in Woodward manual
82715, Guide for Handling and Protection of Electronic Controls,
Printed Circuit Boards, and Modules.

GECOStoichiometric Manual 03554
vi Woodward

Manual 03554 GECOStoichiometric
Woodward 1
Chapter 1.
General Information
Welcome!
This manual describes the GECO™and GECO Vista Stoichiometric controls.
The GECOStoichiometric control provides precise air/fuel ratio control for
engines using three way catalytic converters to reduce exhaust emissions. It is a
more sophisticated exhaust oxygen feedback control system because it includes
continuous oxygen sensor diagnostics, catalyst over-temperature & differential
pressure protection, and failsafe operating modes.
Available Woodward Stoichiometric Controls
Woodward Control P/N Enclosure Type Touch Display /
Handheld
9907-865 – GECO
Stoichiometric Hoffman Enclosure Handheld
9907-867 – GECO
Stoichiometric Panel Assembly Handheld
9907-879 – GECO Vista Hoffman Enclosure Touch Display
GECOStoichiometric System Features
Microprocessor-based
o9–30 Vdc supply operation voltage for GECO Stoichiometric
o19.2–28.8 Vdc supply operation voltage for GECO Vista
Pre-catalyst, closed loop, exhaust oxygen feedback control
Post-catalyst, exhaust oxygen feedback, cascade control allowing
adaptation to changing catalyst performance
Post-catalyst exhaust oxygen control set point variable with engine load
Adjustable fuel valve dithering algorithm for better catalyst control
Catalyst temperature monitoring to protect the catalyst from engine fueling
malfunctions (2 K-type thermocouples)
Catalyst differential pressure monitoring to indicate ash build-up and help
meet regulatory requirements
Open loop valve positioning in event of critical oxygen sensor malfunction or
large transient load changes
Self-learning capability that “remembers” appropriate fuel valve positions
over engine load range providing near-perfect failsafe operation
Capable of driving up to two fuel metering valves for “V” engine
configurations
Utilizes low-cost L-Series fuel trim valves capable of “Full-flow’ fuel trim
strategy that extends the AFR adjustment range
RS-485/Modbus
®
* communications support for data transmission
Full color HMI screen, enabling monitoring without hand-held terminal
(available on the GECO Vista model)
Comprehensive diagnostics including continuous oxygen sensor health
monitoring
Manual closed loop enable switch
Alarm relay
Shutdown relay
LED Driver for Power Indication, Alarm & Shutdown

GECOStoichiometric Manual 03554
2 Woodward
Plug-in terminal strip connectors for ease of installation
CSA Listed for Class I, Division 2, Groups A, B, C, and D in Canada and US
*—Modbus is a registered trademark of Schneider Automation Inc.
Definitions of Terms and Abbreviations
atm
°C
catalyst
CLE
closed loop (CL)
duty cycle
ECU
EGO sensor
EGT sensor
equivalence
ratio
°F
GECO
G-lead
HEGO sensor
kPa
kW
kW transducer
Atmosphere (pressure), 14.7 psia
at sea-level (101 kPa, 1.01 bar)
Degree Celsius
Also known as a catalytic
converter, a flow-through chemical
reactor mounted in the exhaust
stream to decrease harmful
emissions; three-way refers to
simultaneous oxidation of carbon
monoxide (CO) and hydrocarbon
(HC) along with reduction of
oxides of nitrogen (NO x ) at fuel
mixtures close to stoichiometry
Closed Loop Enable (switch)
Control using feedback signals
from the controlled parameter
Percent of on time per total on/off
cycle time
Electronic Control Unit
Exhaust Gas Oxygen sensor
Exhaust Gas Temperature sensor
(K-type thermocouple)
Normalized air/fuel ratio used to
compare different fuels relative to
stoichiometry
phi (φ) = (A/F)
stoich
/ (A/F)
actual
lambda (λ) = 1/phi
Degree Fahrenheit
Gas Engine Control
Ignition pulse output signal (high
voltage) used for engine speed
measurement
Heated Exhaust Gas Oxygen
Sensor
kilopascal (pressure)
kilowatt (power)
A transducer that measures the
output power of the electrical
generator and converts that
measurement to a proportional
4–20 mA signal
lambda (λ)
lb-ft
lbm/hr/l
LCD
LED
MAP
MAT
Mdot
MPU
Nm
open loop
PC
psi
psia
psig
RPM
RTV
stereo
stoichiometric
TC
W
See equivalence ratio
Pound-feet (torque)
Pounds per hour per liter
(mass flow rate per liter of engine
displacement)
Liquid Crystal Display
Light Emitting Diode
Intake Manifold Absolute
Pressure—an indicator of engine
load
Intake Manifold Absolute
Temperature—used to determine
mixture density
Mass flow rate
Magnetic Pickup speed sensor
Newton-meter (torque)
Control without feedback from any
controlled parameters
Personal Computer
Pounds per square inch (pressure)
psi absolute pressure
psi gauge pressure (over ambient)
Revolutions Per Minute (rotational
speed)
Room Temperature Vulcanizing
(silicone sealers)
Two separate fuel systems for each
bank of cylinders including intake
manifolds, throttles, and carburetors
Chemically balanced mixtures (all
reactants mutually consumed)—in
the case of engine air/fuel mixtures,
just enough air to theoretically burn
all the fuel
Thermocouple (see EGT)
Watt (power)

Manual 03554 GECOStoichiometric
Woodward 3
GECOStoichiometric Control Specifications
Power Supply
Power Supply Operating Voltage: 19.2–28.8 Vdc (24 Vdc nominal) (GECO
Vista model)
9.0–30.0 Vdc (12 Vdc or 24 Vdc nominal)
(GECO Stoichiometric model)
Power Supply Rated Voltage: 19.2–28.8 Vdc (class 2) (GECO Vista
model)
8–32 Vdc (GECO Stoichiometric model)
Power Consumption: 83 W maximum (application specific)
(GECO Vista model)
70 W maximum (application specific)
(GECO Stoichiometric model)
Inputs: 2 Unheated Zirconia Exhaust Oxygen
Sensors (EGO) (0–1 Vdc), p/n 6910-315 or
equivalent
1 Heated Zirconia Exhaust Oxygen Sensor
(HEGO) (0–1 Vdc), p/n 6910-316 or
equivalent
2 K-type Thermocouples, p/n 1736-919 or
equivalent
1 Intake Manifold Absolute Pressure Sensor
(0–5 Vdc; 0–3 bar absolute), p/n 6910-314
1 Differential Pressure Sensor(1–5 Vdc;
0–15“ H
2
O)
1 Magnetic Pickup, p/n 5430-929 or
equivalent (0.20–100 Vrms; 8–10 000 Hz)
1 “G-lead” pulse from ignition system (±250
V max)
Outputs: 2 PWM Fuel Metering Valves, p/n 1310-923
1 Alarm Relay (Solid State relay Form C;
250 V @ 75 mA max non-inductive load)
1 Shutdown Relay (Solid State relay Form
C; 250 V @ 75 mA max non-inductive load)
Diagnostics: Power Supply Voltage
Oxygen Sensor Health
Oxygen Sensor Heater Circuits
Manifold Pressure Sensor
Closed-Loop Functions
Catalyst Differential Pressure
Catalyst Temperature
Control Failsafe
Operating Modes: Pre-catalyst exhaust oxygen closed loop
control on failure of post-catalyst oxygen
sensor
Open loop valve positioning mode on failure
of pre-catalyst exhaust oxygen sensor
Valve default position on failure of manifold
pressure sensor
Communications: RS-232 Hand-Held Interface 6-Pin RJ-12
RS-232 PC Interface DB9F
RS-485/Modbus Slave Data Transmission

GECOStoichiometric Manual 03554
4 Woodward
Environmental Specifications
Temperature Ranges:
Ambient Operating
Temperature: 0 to +40 °C (+32 to +104 °F) (GECO
Vista model)
–40 to +70 °C (–40 to +158 °F) (GECO
Stoichiometric model)
Storage Temperature: –40 to +105 °C (–40 to +221 °F)
Enclosure: 305 x 254 X 127 mm (12 x 10 x 5 in)
NEMA 12/13, IP55, Quick-Release
Latches
Regulatory Compliance:
GECO Stoichiometric
CSA Certified for Class I, Division 2,
Groups A, B, C, & D, T5 at 70 °C
Ambient. For use in Canada and the
United States.
CSA Certificate 1214651
GECO Vista
CSA Certified for Class I, Division 2,
Groups A, B, C, & D, T4A at 40 °C
Ambient. For use in Canada and the
United States.
CSA Certificate 1214651
Tecknocraft Trim Valve Environmental Specifications
Operating Temperature: –40 to +125 °C (–40 to +257 °F)
housing temperature
Vibration: Sine Sweep—10-2000 Hz at 10 g’s
peak-to-peak
L-Series Trim Valve Environmental Specifications
Operating Temperature: –40 to +125 °C (–40 to +257 °F)
housing temperature
Vibration: Sine Sweep—10-2000 Hz at 10 g’s
peak-to-peak

Manual 03554 GECOStoichiometric
Woodward 5
Chapter 2.
System Description and Application
GECO™Stoichiometric Air/Fuel Ratio Control
The GECO™Stoichiometric gas engine control is a microprocessor-based
air/fuel ratio control for carbureted, four-stroke, gaseous-fueled engines operating
with a near-stoichiometric air/fuel ratio. It is designed to work in conjunction with
a three-way catalytic converter to efficiently reduce exhaust emissions. By
automatically maintaining an optimum air/fuel mixture, emissions compliance is
achieved and catalyst life is maximized without operator supervision.
Figure 2-1. System Components
In supplementary mode, the carburetor remains in place on the engine, adjusted
slightly lean. During operation, the GECOStoichiometric control adds fuel
through a supplementary fuelling system to bring the air/fuel mixture to the
precise value that will make the catalytic converter most efficient. In full-flow
mode, the carburetor remains in place on the engine, adjusted slightly rich.
During operation, the GECO stoichiometric control restricts flow using a full-flow
trim valve located inline upstream of the carburetor to bring the air/fuel mixture to
the required precise value that will make the catalytic converter most efficient.
A catalyst that simultaneously eliminates hydrocarbons (HC), carbon monoxide
(CO), and oxides of nitrogen (NO
x
) is referred to as a “three-way” catalyst. The
use of a three-way catalyst will reduce the emissions of a stoichiometric engine.
However, for these reductions to be reliable and maximized and to protect the
catalyst element from premature aging or damage, a very precisely controlled
air/fuel ratio is required.
If a three-way catalyst receives exhaust gas containing emissions in the
proportions shown in the “Stoich” window of Figure 2-2, the resulting emissions
exiting the catalyst will be reduced to the levels shown in Figure 2-3.
The exhaust gas oxygen sensor (EGO) will generate a voltage signal that is
characteristic of this ideal stoichiometric window. The GECO control will use this
voltage value to keep the engine at this correct air/fuel ratio. For natural gas this
voltage is usually around 0.780 V.

GECOStoichiometric Manual 03554
6 Woodward
Figure 2-2. Pre-Catalyst Emissions Figure 2-3. Post-Catalyst Emissions
Pre-Catalyst Exhaust Oxygen Control
The GECO control increases or decreases the fuel flowing through the
supplementary fuel system to hold the EGO1 (and EGO2 if present) sensor
voltage at this target value.
+
EGO1
Base
+
-
+
Fuel
Trim
Valve
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
EGO1 Target
Figure 2-4. Basic Control Logic for Pre-catalyst EGO Control
Post-Catalyst Exhaust Oxygen Control
In order to assure optimal catalyst performance over time as conditions vary and
the catalyst element ages, the GECOStoichiometric control has an “Adaptive
Control” loop that uses feedback from a second oxygen sensor in the exhaust
downstream of the catalyst element.
This post-catalyst control loop “adapts” the primary pre-catalyst control to
changes in fuel, catalyst, and environmental conditions that are reflected in the
post-catalyst oxygen concentration. A post-catalyst oxygen sensor voltage of
0.720 V is a typical post-catalyst control loop set point (or EGO3 Base value).

Manual 03554 GECOStoichiometric
Woodward 7
+
Post-Cat
Exhaust
Oxygen
(EGO3)
EGO1
Base
+
-
++
+
-
Fuel
Trim
Valve
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
Filter
EGO3
Target
EGO1 Target
+
EGO3
Base
+
Figure 2-5. Basic Control Logic for Post-catalyst EGO Control
EGO3 Offset
This EGO3 Base value may vary several millivolts from engine to engine, catalyst
to catalyst, and load to load. Some engines operate with varying loads. In order
to keep such an engine and catalyst at optimum performance, the EGO3 Base
value may need to be adjusted. The required adjustment can be entered into the
EGO3 Offset table in the GECO control so that it can adjust the EGO3 Base
value by adding the offset to the base value at different loads. The GECO control
keeps track of engine load by monitoring the intake manifold pressure (MAP) and
engine speed (MPU). The intake manifold pressure and engine speed are used
to calculate an approximate engine fuel flow is then used as a load indicator. The
load range of the engine is divided into eight segments. An EGO3 Offset value
can be manually entered for each of these load levels with this feature. The
EGO3 Base value can be offset to provide the optimum EGO3 Target value over
the entire operating range of the engine.
+
Post-Cat
Exhaust
Oxygen
(EGO3)
EGO1
Base +
-
++
+
-
Fuel
Trim
Valve
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
Filter
EGO3
Target
EGO1 Target
+
EGO3
Base +
EGO3 Offset Table
Fuel Flow EGO3
0.00 -0.010
2.00 -0.005
4.00 -0.000
6.00 +0.005
8.00 +0.010
10.00 +0.008
12.00 +0.007
14.00 +0.005
Intake
Manifold
Pressure
(MAP)
Fuel Flow
Estimation
Speed
Figure 2-6. Control Logic with EGO3 Offset

GECOStoichiometric Manual 03554
8 Woodward
Open Loop Control Mode
The open loop control mode will control the air/fuel ratio of the engine without the
closed loop EGO measurement. This mode is less accurate than the closed loop
mode but it is more accurate than the carburetor alone. This mode positions the
fuel control valve to predetermined values based on the load of the engine. The
control measures engine load by using the intake manifold pressure and engine
speed to calculate fuel flow into the engine. This calculated fuel flow represents
engine load. It is then used in a table of the control valve position versus fuel
flow. This table is called the Valve-Learn table. The Valve Learn table stores
valve operating positions at various points over the engine load range. The table
has eight load points. Values in between load points are interpolated.
Intake
Manifold
Pressure
(MAP) Fuel
Trim
Valve
Valve Position
Table
Fuel Flow Valve 1
0.0 40.0
2.0 45.0
4.0 50.0
6.0 60.0
8.0 65.0
10.0 70.0
12.0 72.0
14.0 73.5
Open Loop/
Closed Loop
Fuel Flow
Estimation
Speed
Closed Loop
Control
Figure 2-7. Control Logic for Open Loop Control
The open loop control mode can be used as the primary control mode, but it
mainly serves as a backup to the pre-catalyst closed loop control mode. If the
EGO1 or 2 sensor fails, the control automatically defaults to the open loop mode.
The values in this table are normally entered manually during initial control
calibration. In some situations they can be entered automatically. This is called
the Valve-Learn function, it is not initially active. It must be activated in the control
if this feature is required.
Valve-Learn Function
Over time, if fuel BTU content changes or environment conditions change,
normal “Closed Loop” or “Closed Loop - Adaptive” control operation will maintain
the fuel control valve at the optimum position for the current operating conditions.
However, in Open Loop mode, the Valve-Learn table will lose its accuracy if it is
not kept up-to-date. To prevent this, the Valve-Learn function can continuously
learn new optimum control valve positions. As long as the “Closed Loop” function
is active the current optimum valve position is re-entered into the table whenever
conditions are stable and closed loop accuracy is maintained. If a problem should
develop with the EGO1 or EGO2 sensors, the “Open Loop” control mode will
then select from the table the valve positions that match current conditions.

Manual 03554 GECOStoichiometric
Woodward 9
Intake
Manifold
Pressure
(MAP)
+
-
Fuel
Trim
Valve
Valve Position
Table
Fuel Flow Valve 1
0.0 40.0
2.0 45.0
4.0 50.0
6.0 60.0
8.0 65.0
10.0 70.0
12.0 72.0
14.0 73.5
Open Loop/
Closed Loop
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
Fuel Flow
Estimation
Speed
EGO1 Target
Open Loop
Figure 2-8. Control Logic for Valve-Learn Function
Fuel Valve Dithering
It has been shown that “dithering” the Air/fuel ratio into the catalyst increases the
window of air/fuel ratio variation to enhance the performance of the catalyst. The
GECO includes parameters to adjust the amplitude and frequency of the
dithering to optimize the oxygen storage capability of the catalyst. This strategy
widens the window of operation and will allow the EGO sensors to drift more
without reducing the efficiency of the catalyst.
Diagnostics and Monitoring
For system reliability the GECO control monitors sensor inputs and control
outputs for high and low failure conditions as well as extensive self-diagnostics
for system functionality. Alarm or shutdown control outputs are available to allow
integration into an engine or system control panel for component failure or
emissions compliance requirements. These alarms are configured in the
software. There is an alarm and shutdown LED output as well as an alarm and
shutdown relay.
In addition, the GECO control has oxygen sensor health monitoring. This function
can assess the remaining activity of the oxygen sensors, and preventative
maintenance can be planned before a sensor failure occurs.
Communications
Communication with the system is via a computer (PC) interface or by the hand-
held terminal. Control setup and tuning is accomplished through the PC interface
screens (see Figure 2-9).

1
╔
═En
║
Sp
║
M
A
║
TC
║
TC
║
Co
║
Co
║
Ru
║
Ru
║
Ho
║
DC
╠
═O
x
║
║
║
E
G
║
E
G
║
E
G
║
E
G
║
A
d
║
Va
║
Va
╚
══
═
GEC
O
10
The
P
inclu
d
loggi
n
gene
r
1
GECO Stoi
c
gine══════
═
eed
A
P
1
Upstream
Dnstream
ntrol1
O
ntrol2
O
nMode
R
n Time
0
ur Meter
Power
2
x
ygen Senso
r
G
O unfilt
G
O filter
G
O target
G
O health
d
aptive
lve Cmd
+
lve Cur
═
══════════
═
The
G
or S
C
functi
o
confi
g
O
Stoichiom
e
P
C software
a
d
ing status in
d
n
g. The hand
-
r
ally not suita
c
hiometric
═
══════════
╦
1200 rpm
║
1
0.00 psia
║
1013 °F
║
1091 °F
║
O
PEN LOOP
║
O
PEN LOOP
╠
R
UNNING
║
0
073:19:01
║
120.8
║
2
3.9 volts
║
r
s═════════
╩
Engine-O
u
Bank1 B
a
0.791 0
.
0.783 0
.
0.782 0
.
100
+
55.16 +5
2
0.61
0
═
══════════
═
Figur
e
G
ECO contro
l
C
ADA system
o
n is for info
r
g
uration or tu
n
e
tric
a
lso includes
m
d
icators and
d
-
held termina
ble for set-u
p
Figure
Air/Fuel C
o
╦
═Shutdown
s
║
ClearAll
║
TC Upstr
e
║
TC Dnstr
e
║
║
Controll
e
╠
═Status/C
o
║
Valve St
a
║
Shutdown
R
║
ClsdLoop
S
║
ManualCo
n
╩
═════════
═
u
t
C
a
nk2 Ban
k
.
749 0.
.
782 0.
.
782 0.
98
+
0
2
.91
0
.66
═
═════════
═
e
2-10. PC S
o
Modb
u
l
is also capa
b
. The commu
r
mation distri
b
n
ing.
m
any helpful
d
ata monitori
n
l allows only
v
p
and calibrati
2-9. PC Co
m
o
ntrol Moni
s
══════════
═
High
e
am OK
e
am OK
Misc
e
r OK
o
ntrol═════
═
a
te HOLDI
N
R
elay OFF
S
wtch ON
n
trol OFF
═
══════════
═
C
at-
O
ut
k
1+2(EGO3)
725 volt
s
723
v
olt
s
721 volt
s
95 %
0
.00 %
%
amps
═
══════════
═
o
ftware Tool
D
u
s Com
m
b
le of sendin
g
nication prot
o
b
ution and is
n
features for
s
n
g, and real-
t
v
ery limited
a
on.
m
munications
tor
I
D:545
5
═
═
╦
═Fuel C
o
║
ClearAl
║
Valve1
║
Valve2
║
Adapt
║
Valve1
═
═
╣
Valve2
N
G
║
DC Pow
e
║
MAP Se
n
║
║
TC Ups
t
═
═
╣
TC Dns
t
║
CJC se
n
║
s
║
ECU Pr
o
s
║
Trigge
r
s
║
║
EGO1
║
EG
O
2
║
EGO3
║
═
═
╩
═══════
═
D
isplay Scre
e
m
unicatio
g
information
o
col is Modb
u
n
ot intended
s
ystem troubl
t
ime plotting
a
a
ccess to sett
5
-111-
N
W 20
0
o
ntrol Alar
m
l Hig
h
Limit OK
Limit OK
Limit OK
Curnt OK
Curnt OK
e
r OK
n
sor OK
Ope
n
t
ream OK
t
ream OK
n
sor OK
Mis
c
o
cessor OK
r
OK
Hig
h
OK
OK
OK
═
══════════
═
e
n Example
n
to a supervi
s
u
s, ASCII or
R
or capable o
f
Manual
Woo
eshooting,
a
nd
ings and is
0
1/05/15
m
s═════════
═
h
Low
O
K
OK
OK
OK
OK
OK
OK
n
LowExp
OK
OK
OK
c
h
Health
OK
OK
OK
═
══════════
═
s
ory control
R
TU. This
f
remote
03554
dward
═╗
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
║
═╝

Manual 03554 GECOStoichiometric
Woodward 11
System Diagram Examples
Figure 2-11. GECO System for Single Carburetor Engine

GECOStoichiometric Manual 03554
12 Woodward
Figure 2-12. GECO System for Dual Carburetor Engine