When testing a vehicle with a manual transmission using the EIS machine, in which gear should the tests be performed?

The correct choice of performing emissions testing on a vehicle with a manual transmission in 2nd gear is based on achieving the optimal engine operating conditions for accurate results. Testing in 2nd gear is often recommended because it helps to simulate real-world driving conditions more closely than other gears.

In this gear, the engine is typically at a speed that allows for proper combustion and emissions control systems to function effectively without being too labored or under too much load. This balance helps ensure that the emissions readings reflect the vehicle’s performance in normal driving scenarios.

Using 1st gear might cause the engine to operate at higher RPMs than necessary, which could skew the emissions readings. Similarly, testing in higher gears, like 3rd or above, may not provide adequate engine load and could lead to lower RPMs that don't represent typical vehicle operation during acceleration. Therefore, 2nd gear is optimal for emissions testing as it provides a realistic scenario to evaluate the vehicle’s emissions performance reliably.