The Highwayman

“My truck was running rough just before it stalled out,” the driver told us. It was a 2017 Kenworth and the driver, Max, was really pleased to see us. He called Dewey’s shop while we were having lunch.

When we got out there, we verified the concern. The Cummins engine cranked but it wouldn’t start. Milton conducted a thorough visual inspection while Dewey questioned the driver. No add-on equipment and no previous, recent service had been performed. The engine oil level was good and no parasitic load while cranking. Engine cranking speed was good. These technicians wanted a recommended diagnostic procedure to follow, so I offered my typical routine.

I check ground circuits first because the other circuits will use ground to verify they are functioning properly.  This includes battery cable connections.

Low reference circuits are checked next because the other circuits will use this low reference circuit or ground circuit to verify they are functioning correctly. A low reference circuit test requires the ground circuit between the control module and the battery negative terminal is intact. Testing for continuity on a reference low circuit oftentimes requires certain pre-conditions to attain a legitimate reading. Some conditions could include the ignition to be off for a certain amount of time, the ignition key needs to be out of the ignition cylinder, the scan tool to be unplugged or require a fuse to be removed in order for the module to power down.

The grounds were checked for integrity on the Kenworth—they passed a good visual inspection, and a voltage drop test.

Once the grounds were checked, we focused on the voltage circuits starting with B+ voltage—why? Because the Ignition, AC, voltage reference, and control circuits require a functioning B+ circuit and B+ is direct battery voltage to an ECU or component. A switch type device does not interrupt this circuit (Un-switched). This includes battery voltage circuits that pass through a fuse, ECU, component, or connection. The B+ circuit test is referenced to a ground or low reference circuit. It really depends on the circuit.

The B+ circuits all had the proper voltages, and the voltages were clean when checked with my scope.

The next voltage circuits that we tested were ignition voltages because the voltage reference, any AC circuits, and control circuits require ignition voltage to be present. An ignition circuit provides a switched voltage to an ECU or component when the ignition is in the OFF, ACCESSORY, ON or CRANK positions.  This includes ignition circuits that pass through a fuse, ECU, component, or connection.  When testing ignition circuits, I reference the wiring schematic as to the ignition switch mode or position needed to achieve a valid reading. The ignition circuit test is referenced to the ground or low reference circuit and requires a functioning B+ circuit.

Do you notice that each test builds on the previous test?

Since the Kenworth had inverters, we checked all AC outputs. They were all consistent and clean. The AC circuit test is referenced to the ground or low reference circuit and requires a functioning ignition circuit, which was checked previously.

We inspected and verified the correct fuel pressure in the tanks; the OEM fuel shutoff valve was open. There were no component changes made to the CPL or engine components. Fuel regulator outlet pressure was good, within specs. The fuel regulator outlet pressure was within specs.

As you can plainly see, there is nothing magical about diagnosis. It’s always about a plan.

The fuel pressure after the fuel shutoff valve is detected by an engine fuel regulator outlet pressure/temperature sensor. The ISL G Module incorporates a boost reference low pressure regulator that helps in fuel control optimization across a full range of fuel flows. It can bump fuel pressure at the fuel control valve responding to an increment of boost pressure. An external pneumatic hose with fittings provides boost reference to the low pressure regulator to sealed end cap.

So far we were coming up with nothing. I’d gotten into diesel fuel sampling. I don’t have or need a Bacon Bomb Thief, but I do have a field test kit. I can check for both suspended and free water in fuel, and microbial growth as well.

I’m sitting in the Kenworth’s cab, trying to figure this one out, when I spotted it on the floor. I picked it up.

“What are these—feathers?” I asked Max, the driver.

“Yeah—duck bottom feathers, from near the preen gland,” he said.

“I never heard of them,” I said, “What are they used for?”

“Well, they’re buoyant,” Max said, “due to preen oil produced by the preen gland. I use them to tie dry flies.”

“For fly fishing,” I said. Max nodded.

“I bought them from the guy who tuned my engine the other day,” he said.

There it was—the answer! “Hold everything!” I said. “What are you talking about?”

“I’m at a truck stop, checking my rig over, when a guy in a new BMW SUV pulls up next to me. He was one fancy dresser, I’ll say that,” Max said. “He wore a lambskin leather blazer and one of those derby bowler hats. He looked well-to-do and said he was able to program my truck to improve my fuel economy and performance for only fifty bucks with a money-back guarantee.”

This was it. This was what we were looking for.

“At first I was doubtful, but then I saw his fly-fishing rod in his BMW, and since I’m an avid fisherman, we got to talking. The guy threw in a bag of Cul-de-canard in the deal—for free.”

This guy preyed on truckers. What he did was used his laptop to go into the ECM, maxed out the injectors and ruined the flow rates. Sure, the engine gained some power, but it wasn’t smooth power and the idle roughened up. Eventually the engine loaded up and finally wouldn’t start.

“I asked you if anyone worked on your truck and you told us no,” I said to Max.

“Right—nobody worked on my rig—all this guy did was reprogrammed my computer. That’s not the same thing, is it?”

See what you need to be wary of? Had I not seen those duck feathers, I might have missed this one. I reset the injector flow rates, cleared the lines, recommended an oil change and made the driver happy until he saw my bill. He wanted to square his debt by giving me the bag of feathers. I explained to the driver that I charged for diagnostic time. The software program that “Dick Turpin” used was clever. It changed the injector flow rates but showed a modified value on the data PIDs, to mask the high flow rates. Dick Turpin was clever. I call him that after Dick Turpin, the English highwayman whose exploits were romanticized following his execution in York. A highwayman was a robber who stole from travelers. At one of the diesel fuel stops, the manager told me of “an Englishman” who used a Bacon Bomb Thief to sample his storage tank and tried to sell him some snake oil.

The feathers “quacked” this caper.