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Title / Demonstrate knowledge of engine tuning procedures and equipment malfunction causes on CNG fuelled vehicles
Level / 4 / Credits / 2
Purpose / This theory-based unit standardis for people in automotive and related industries. People credited with this unit standard are able to demonstrate knowledge of engine tuning procedures and equipment malfunction causes on compressed natural gas (CNG) fuelled vehicles.
Classification / Motor Industry > Automotive Fuel Systems and Exhaust
Available grade / Achieved
Guidance Information
1Legislation and publications relevant to this unit standard include but are not limited to – Health and Safety in Employment Act 1992; Traffic Regulations 1976; Land Transport Rules: Vehicle Repair 1998, Rule 34001; Vehicle Standards Compliance 2002, Rule 35001/1; Vehicle Standards Compliance Amendment 2005, Rule 35001/2; New Zealand Standard AS/NZS 2739:2003 Natural gas (CNG) fuel systems for vehicle engines.
2Land Transport Rules are produced for the Minister of Transport by Land Transport New Zealand. These rules are available online at
New Zealand Standards are available from Standards New Zealand, Private Bag 2439, Wellington; phone 04 498 5990; or website
3Definitions
CNG equipment manufacturer instructions refer to specifications and instructions provided by the equipment manufacturer for the correct installation and operation of the CNG component(s) or system(s) provided by that manufacturer.
Company requirements refer to instructions to staff on policy and procedures which are documented in memo or manual format and are available in the workplace. These requirements include but are not limited to – company specifications and procedures, work instructions, manufacturer specifications, product quality specifications, and legislative requirements.
Outcomes and performance criteria
Outcome 1
Demonstrate knowledge of engine tuning procedures and equipment malfunction causes on CNG fuelled vehicles.
Performance criteria
1.1Problems that may affect engine operation following the fitment of conversion systems are described in accordance with CNG equipment manufacturer instructions.
Rangemalfunctions related to fuel supply and gas usage.
1.2Problems that may occur with CNG components in service are described in accordance with CNG equipment manufacturer instructions.
Rangemechanical and electrical faults, lack of servicing, external problems affecting performance.
1.3The procedure to perform on-road acceleration tests is described in accordance with company requirements.
Rangehesitation, misfiring, flat spots, overall performance.
1.4The use of a rolling chassis dynamometer and an infra-red exhaust gas analyser for carrying out adjustment and test procedures on an engine operating on dual fuel is explained in accordance with CNG manufacturer equipment instructions.
Rangeengine under loading conditions throughout revolutions per minute (RPM) range.
1.5The modification requirements for vehicles to run on dedicated CNG are explained in accordance with CNG manufacturer equipment instructions.
Rangeincludes but is not limited to – removal of existing fuel system components, fitting of gas components, alterations to compression ratio, ignition components, ignition timing, exhaust emission controls, air intake systems, valve and valve seat modifications, turbocharging, intercooling.
1.6Legislative requirements when carrying out repairs and maintenance to vehicles equipped with CNG fuel systems are described.
RangeAS/NZS 2739, Traffic Regulations, Land Transport Rules (Vehicle Repair, Vehicle Standards Compliance).
1.7Procedures to maintain a CNG fuel system are described in accordance with service information and legislative requirements.
Rangefilter cleaning, regulator draining, air filter, leak detection, security of components, hose condition, mixer attachment.
Replacement information / This unit standard and unit standard 24184 replaced unit standard 952.This unit standard is expiring. Assessment against the standard must take place by the last date for assessment set out below.
Status information and last date for assessment for superseded versions
Process / Version / Date / Last Date for AssessmentRegistration / 1 / 25 January 2008 / 31 December 2020
Review / 2 / 26 April 2018 / 31 December 2020
Consent and Moderation Requirements (CMR) reference / 0014
This CMR can be accessed at
MITO New Zealand IncorporatedSSB Code 101542 / New Zealand Qualifications Authority 2018