Finding the root cause of: an intermittent engine problem

In this series of troubleshooting postmortems, technicians will explain how they fixed a common issue on commercial vehicles.

The Challenge

A Detroit-powered Freightliner tractor that had stopped running and would not start was brought to I-505 Truck and Trailer Repair in Vacaville, California.

After gaining a reputation for handling complex repairs, Kirtis Burroughs was assigned the job. The technician has more than three decades of experience servicing and repairing heavy-duty commercial vehicles. This would be one of his most vexing missions ever, he said after finally figuring out the issue.

Initial diagnostics on the truck revealed the presence of metal shavings in the fuel tank and fuel filters, Burroughs reported. That led to the replacement of the fuel injection pump and the fuel filter module. The fuel system was flushed, including the tanks. After those procedures, the engine started, the truck was road tested without experiencing any problems, and the customer was called to pick up the vehicle.

“About 15 minutes after the customer took the truck, they returned to the shop, this time complaining of an intermittent loss of throttle and an engine light that was on,” Burroughs related. “They also reported that the same issues had occurred prior to the fuel system failure.”

The Solution

After connecting a laptop with diagnostic software to the unit, Burroughs found an active fault code for the J-1939 data bus indicating a loss of communication with the vehicle’s ABS module. Further diagnosis indicated an internal problem with the module, so he installed a test unit and road tested the vehicle without experiencing any problems.

After installing and programming a new module, it was time for another road test. This was uneventful, so the customer was advised to drive the truck. The driver returned saying they had experienced the same loss of power, but this time without any engine warning light.

'[T]here is a huge sense of accomplishment when you finally solve a painful, intermittent problem,” noted Kirtis Burroughs after a grueling day of troubleshooting a Detroit engine. — "[T]here is a huge sense of accomplishment when you finally solve a painful, intermittent problem,” noted Kirtis Burroughs after a grueling day of troubleshooting a Detroit engine.

Burroughs quickly determined that there were no current active fault codes. He went on a road test with the customer to verify the complaint. The same problem occurred three times in five miles.

The next step Burroughs took was to contact Detroit, who advised him to road test the vehicle and record the data log. After reviewing that information, the manufacturer advised Burroughs to recalibrate all modules and install new software, including some overdue updates.

Following the data upgrade, the vehicle was road tested again. The same problem occurred as the engine continued to lose power. Another road test log file was sent to the manufacturer and their advice was to replace the clutch switch. Still another road test indicated that the problem was still not resolved, but after reviewing the latest road test log, the manufacturer suggested that Burroughs check the connections on the intake manifold pressure sensor.

After finding that the intake pressure circuit had been repaired using crimp and shrink butt connectors, Burroughs removed the connectors, soldered the wires together and applied shrink tube. But this time he didn’t even have to road test the vehicle, as the problem occurred driving around the yard.

At the manufacturer’s direction, he then proceeded to replace the EGR Delta P sensor. A subsequent drive around the yard and a 45-minute road test did not turn up any problems. Success at last.

“The manufacturer never could tell me why they had me replace the Delta P sensor, other than there was a strange wiggle in the file for the Delta P when the derate occurred,” Burroughs said. “But I didn’t really care what was wrong with the sensor. I was happy to be able to release the vehicle to customer and not hear a word since.

“At one point I was getting very frustrated and wanted to give up on this vehicle, but that’s not my style,” Burroughs continued. “I believe this was one of the top ten issues I’ve faced over the past 35 years as a heavy-equipment technician, but there is a huge sense of accomplishment when you finally solve a painful, intermittent problem.”

The Technician

Kirtis Burroughs, who joined the team at I-505 Truck and Trailer Repair a few months earlier, served as a technician, foreman, warranty administrator and shop manager at another shop for more than 27 years before that facility closed its doors. Along with his 18-year-old daughter Natalee, he also operates Diesel Guru Diagnostics in Napa, California.

I-505 Truck and Trailer Repair is a service provider for Henner Tank Lines, its parent company. The shop also offers maintenance and repairs for other fleets, all makes and models of trucks, tractors and trailers, and provides breakdown assistance. The operation is housed in a new 12,000-sq.-ft. facility with pull through express lane for inspections and regular service, four half bays for repairs, and has an 80-ft. drive-through wash bay.