"We've gone out with an all-out effort to train our technicians," he said. "So there's a lot more coding today making sure the system is doing what it's supposed to do, and coming down the pike you've got on-board diagnostics that demand that you keep track of situations that aren't normal, even if it's only for a few seconds. If you have a valve that's not responding or a turbo that's not responding correctly, or immediately, even though it's in the realm of doing a good job, we still take note of that.
"You could get into a situation where the EGR says, 'I've got enough of a problem here that I'm going to go into non-EGR mode and continue on,' so the control system does it's homework," Blake explained. "So, when you're trying to understand what's going on, whether it's a driver complaint or not, you need a step-through method to do a good job with this. There's no more second-guessing; you really need to go through the diagnostic trees and the fault process to troubleshoot the engine correctly.
"Initially, the sensors were a weak link in the system, and when the sensor goes out, it starts telling the engine bad information. Then you have obviously some problems," he said.
"If you think you have a situation you can look at the fault tree and go through it," he continued. "For instance, we had some turbocharger speed sensors that were going bad, and they were driving the turbochargers crazy. It's an on-off deal where it's supposed to be monitoring the turbocharger's speed. You can look at that and start unpugging sensors and start looking at what it's telling us in certain conditions. So there are ways to troubleshoot sensors, if you start getting too many stupid faults, or you get a fault that says you don't even have a supercharger speed anymore.
"Generally the turbochargers are running between 20,000 and 30,000 RPM at idle," Blake said. "If you're not getting that kind of speed when you're looking at these diagnostic reports from the diagnostic tools, then you have to say 'It looks like we've got a problem here.'"
"What we tried to do in the training manual was look for the common problems, and then tell people, maybe this is what you ought to be looking for in this and this circumstance."
Blake said that the Variable Pressure Output device re-quires a dedicated air source or "it will drive the EGR nuts.
"We had some situations where the air systems were plumbed incorrectly, and when you didn't have a single source feed to the air system that controlled both the turbocharger and the EGR valve you'd end up with some pressure spikes, and the control system didn't like that."
Blake also de-scribed an early problem he called "Inlet Control Valve Blowout."
"That was something we discovered recently, and that was part of the air compressor system. That's a bubble of air that's held between the inlet valve and the air compressor when you're not pumping. It's an efficiency thing-when the air compressor's not required to work you retain a little bubble of air in there, which pushes the piston back down. So you have less parasitic loss on the compressor when it's not working, and therefore you get better fuel economy. That's been fixed with a bigger valve; the holes have actually been increased in diameter and there's actually a different gasket in that valve. So although it didn't have anything to do with the EGR system, it affected the efficiency of the EGR engines."