Mission: Accomplished

Fleet Maintenance continues its series of technical articles taken from the technician training presentations from the Fall Meeting of the Technology & Maintenance Council (TMC).

"There was all this hype about pre-buy and fear of the '02 product that was going to be introduced. And now (in September, 2004) we have all these '02 engines running around doing a real good job. It really didn't cause any huge technical hiccups going to this new platform."

These words from Bill Stahl, director of OEM service for Cummins, Inc., sums up the technical presentation given at the Technology & Maintenance Council's (TMC) Fall Meeting last September. Stahl, along with representatives from five other American heavy duty diesel manufacturers, gave a report on the state of "Troubleshooting Post-2002 Diesels," and the news was essentially positive.

In this issue, we'll cover the news from Cummins and Detroit Diesel, and next issue we'll continue with International and other manufacturers.

BILL STAHL, CUMMINS

According to Stahl, fleets have encountered some faults with early production ISX and ISM engines with EGR, but "they have not been mission-disabling."

Stahl went on to detail the technical issues that have been encountered, starting with EGR valve failures on some early engines. "Again, the saving grace was that it was not mission-disabling. It requires a very short period of time to change the EGR valve, and there were always parts available.

"The EGR valve also had a motor shaft problem (a stem seal that could leak), which was probably the worst problem, because you had exhaust gasses going up into the motor and gear box of the little control valve," he explained.

"There was also a sensor pin problem," he continued, "but the point was there were all of these little issues that contributed to the need to change the EGR valve. Most of those were solved in the last part of '03, and then we've made continual improvements up until the end of '04.

"I think the key point out of this list of problems-the EGR valve, the water pump, the injector, the exhaust manifold leakage, white smoke and stumble, the plugged differential tube-is that we came to the party with nine issues, and of those, none of them are mission-disabling," Stahl related. "And, other than the EGR valve failures, the rest of these aren't '02-technology related."

Technicians will notice additions to the ISX and ISM troubleshooting guides, according to Stahl. "When you add sensors, you add troublehooting logic, because you want to find if you have a bad sensor, a bad connection, a bad circuit.

"If it spits out a 432 or 438, it's a matter of the logic in Insite, or a paper fault tree that leads you through the process to fix that'" he said. "If you know the concept of reading a fault and going down through the fault tree to find a problem, once you do that for one fault, it's pretty much the same."

CHUCK BLAKE, DETROIT DIESEL

Chuck Blake, staff application engineer for Detroit Diesel, cautioned that "The EGR en-gine is a fairly complicated machine.

"It's a closed-loop control system, so it actually understands, for instance, EGR flow, so it keeps adjusting itself," he explained. "It's not just, 'At this RPM and at this load, I need this kind of angle on my EGR valve.' No, I want the exact flow that I require at this PRM and this load factor, so the engine continuously adjusts the turbocharger and the EGR valve to get the correct mixture into the engine. Consequently, the program controlling this engine has to be very smart; it's reading a couple more sensors than are normally on a diesel engine; it has to under stand atmospheric conditions better than the previous engine did. So there's a lot more brainpower going on, comprehending the ambient conditions and then satisfying the conditions that are needed to keep the exhaust system legal.

"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."

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