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TEST PROCEDURES AND REASONS FOR FAILURE
Page 19
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A VI tester will check your truck's speed limiter using the following procedure: • Look to see that a limiter 'plate' is securely fixed in the cab—it's acceptable for it to be fitted in the driver's door jam. But if a sticker is fitted on a window and is facing outwards, the details must be able to be read by a person 'of average height'.
• The plate must be clearly (and indelibly) marked with the speed at which the limiter has been set. This may be shown in either mph or km/h.
• Examining the limiter's secu My along wIth its actuating mechanism, wiring and tamperproof seals. The inspection only covers parts that are visible without dismantling.
• The limiter may be wired through the ignition switch. BUT any other device that would allow disconnection of the limiter while driving is unacceptable.
• The tester checks the limiter with the electronic device by first opening the tacho head and plugging the speed simulator jack into the head before closing it again. Seals can only be removed by approved tacho sealing centres or VI staff.
• Using the electronic device, the tester next establishes the !echo's pre-set K-factor, ensuring that it is within +/-50 digits of the K-factor displayed on its calibration plate.
• Starting the engine and running it at 1,200-1,500rpm, the tester then inputs a simulated speed of 80km/h (50mph), checking that the tacho runs at the indicated speed.
• Gradually increasing the speed in 1km/h steps, the tester notes the speed on the simulator's display at which the limiter kicks in—indicated by a drop in engine revs, a change in engine note or a vibration signifying that the fuel supply is being reduced.