The corporation says it needs another 10 of the DL-class engines to cope with increasing freight volumes in the North Island.
Since 2009, KiwiRail has bought 63 of the DL-class engines.
They've been plagued by reliability problems, claims of poor quality and 40 were found to contain asbestos.
In the past 12 months KiwiRail's own figures show none of the engines have met KiwiRail's performance target of 80,000 kilometres Mean Distance Between Failure (MDBF).
The MDBF measures the average distance between failures that cause a delay of 15 minutes or more.
This can be due to a number of causes, including issues with the engine and traction systems, software issues, or relatively minor electrical faults such as with the gauge lighting or air conditioning.
It doesn't necessarily mean major breakdowns.
KiwiRail's chief operating officer Todd Moyle has defended the engines' performance, saying they were not bought off the shelf.
"If you go and buy a locomotive it's not like going and buying a Toyota Corolla. New Zealand's rail network, it's narrow gauge, it's light axle weight and every locomotive type that you purchase is bespoke," he said.
He said the 80,000km mark was not an enduring target, the engines just had to reach that at a point in time.
And even though they were not meeting it, they were doing what KiwiRail needed them to do, Moyle said.
"When we purchase locomotives we set a target and that's for a three-month period. The first of locomotives have met that. They've settled down to a level of 50,000 kilometres MDBF and that's delivering to what our customers need at the moment and it's delivering to our service expectation."
In the first six months of last year, KiwiRail introduced 15 new Generation 2.3 DL locomotives, the fourth batch of the Chinese engines.
But the new engines are the worst performing and did not meet the contract performance target of 80,000 MDBF. As a result, KiwiRail has not made its final payment on the trains.
"They've got to meet a threshold of 80,000 kilometres for us to make the final payment on those locomotives, meet that threshold for three months, and then they settle from there," Moyle said.
"There's a number of factors that influence the Mean Distance Between Failures, some of them are mechanical failures of components, some are the way that the machines are being operated and others are how they're being maintained."
