Ghosts in the Wiring

“I didn’t believe in the paranormal before, but ever since purchasing this car, strange things have been happening,” the driver said, obviously not wanting to be identified. “My wife complained of hearing strange noises, like crumpling paper, coming from the back seat about a month ago.”

The 2016 Regal had been in the shop on numerous occasions for a myriad of electrical conditions and multiple components had been replaced. “The door locks would cycle at times, sometimes the car wouldn’t start, and sometimes the radio would decide to play on its own,” the owner said, as I looked at the repair orders. The radio was replaced, the human machine interface module and the body control module.

There were no bulletins or other documents relating to known problems. There were no modifications, no aftermarket equipment and no other work history prior to the dealer. I found a U0029 (MOST Bus Performance) DTC and a U0001 (High Speed CAN Malfunction).

“There were a bunch of other codes, but I cleared them before you got here,” Tim said. Unfortunately, he did not write them down.

I performed a visual inspection and checked the power distribution components—all were okay. When nothing obvious shows up, I look for the not-so-obvious. I broke out my inspection camera and inside the dash I spotted signs of rodent intrusion. Wires were chewed. Years ago, vehicles were made from metal, glass and plastic and 100% of it was made from petroleum. These days, with “green manufacturing,” cars are made from soy, peanut oil, rice husks and other tasty morsels for critters. In the early 1940s, Henry Ford experimented with making plastic parts for automobiles. These experiments resulted in what was described as a "plastic car made from soybeans." Could you imagine how many toothsome rodents would have loved this car?

After we would perform a series of wire repairs, I suggested that the owner authorize wrapping the wires with rodent-proof tape, treated with capsaicin. Sprinkling crystallized fox or coyote urine around the tires also helps. I also found the source of the noise of crumpling paper: I found an active mouse nest under the rear seat. I carried the critters out to the woods so that they could live out their lives away from human intrusion.

We still had the window and headlamp issue. I noticed that the BCM was getting a request to turn those systems on—but from where? I used my scope to look at the GMLAN data stream and saw minor distortion, but when I decoded the CAN bus, I saw Error frames. Decoding is a good, quick indicator that CAN frames are being transferred between ECUs on the CAN Bus.

If you know the CAN database spec of your vehicle, it will be possible to ascertain which ID belongs to which ECU. There are several ways to ascertain this information The IDs and Data are normally shown in Hexadecimal, which is standard in the digital communications industry, however it is possible to display in Decimal if you wish. Decoding a data bus can be useful for seeing instability by sensing Error Frames. I spotted a problem that at 59.87 seconds after start of collection, Error frames started to occur. In fact, when I got the CAN database for the car, I saw that the coded hex was being misinterpreted by the gateway module as commands to illuminate the headlights and lower the driver window!

The “bad” code was sourced from the EBCM. The noise being put on the CAN bus from the EBCM was causing the issue. Remember the original complaint? It happened with the Power Mode Master (BCM) supposedly powering down. Some of the wiring damage caused the communications enable circuit to trigger the BCM. Terminal fretting at the EBCM connector caused Error Frames to appear on the decoded can bus. Multiple issues made this one a very difficult one to resolve.

“Now,” the driver said, “What about those shadows my wife seems to see at times in the car? Do I need to see someone to exorcise demons from the car?”

“Maybe,” I said, laughing, “Or maybe infrasound is the culprit.”

I experienced the negative effects of infrasound in a hotel room once. I just didn’t like the room for some reason and thought I saw odd shapes. It was due to the blower motor in the kitchenette causing the issue. I kept it on all night to act as a sound machine.

If infrasound hits at just the right strength and frequency, it can resonate with human eyes, causing them to vibrate. This can lead to distorted vision and the possibility of “ghost” sightings. Or, at least, what some would call ghost sightings. Infrasound may also cause a person to “feel” that there’s an entity in the room or vehicle with him or her, accompanied by that aforementioned sense of dread.

I hoped you enjoyed this “ghostly” challenge.

A Matter of Harmonics?

“We can’t visualize vibrations, but we tend to experience the effects of vibration, kind of like electricity,” Linda said. The shop had a high-tech vibration analyzer, embedded with a tri-axial accelerometer and laser tachometer.

“I get into vibration diagnostics because we see plenty of souped-up Duramax trucks down here,” She said.

I knew what she meant. Combustion puts such a forceful load on the crankshaft, it actually elastically deforms each time combustion occurs; fortunately, it fully recovers. An 8-cylinder deforms at least four times per rotation.

“Combustion puts a huge amount of force on each crank web, twisting the metal ahead of itself,” she said.

“Right,” I said, “and then it snaps back and creates harmonic frequencies that travel back and forth through the crankshaft. Normally, the harmonics are controlled so they have negligible effect on the main bearings because they work within a defined range of harmonics,” I said.

“Yes, but I’ve seen modified Duramax-equipped trucks where the harmonics affect the bearings and other parts big-time,” Linda said.

She was right because as the frequencies got closer to the natural frequencies of the components, wear increases tremendously due to uncontrolled oscillations.

“So many times the elastomeric damper can’t handle the modifications,” she said.

It wasn’t the case with the 6.2l engine we were working on. I studied the vibration. With the tri-axis sensor in the analyzer we were using (Fluke), my measuring point was in the seat track. This was a rough idle in drive we were dealing with.

Linda and Jeff explained that it was hard to duplicate the vibration. “Most rough idle in drive concerns are temperature dependent, and can be difficult to re-create at times,” I said. With A/C On, I performed several short heavy launch events from stop to stop to bring the temperatures back up while trying to re-create the rough idle vibration in drive with the meter’s sensor placed on inboard seat track in horizontal and vertical axis. It was picking up an E1.5 disturbance.

E1 is a first order engine vibration, simply engine speed, expressed in Hz (E1 x 60 = RPM). E1 vibrations can be accredited to parts related to engine speed such as flywheel and pulleys. High vibration levels detected at E0.5 can be related to half engine speed components, such as camshafts and associated auxiliaries. Usually, E2, a second order engine vibration happens at twice engine speed and will be the highest level of vibration (for a 4-cylinder engine) given we have two combustion events for every revolution of the crankshaft (two shocks applied to the crank), generating a characteristic high E2.  E2 vibration levels can be attributed to combustion events or components rotating at twice engine speed. On an 8 cylinder engine, E4 would be highest.  Ours was an E1.5, and with the vibration duplicated, at the inboard forward seat track location, it measured approximately 6.5 mg. In other words, we were looking at units of g (acceleration due to gravity)—specifically, milli-g. 
“I know,” Linda said, “I stress how important math is when it comes to diagnosis.”
Linda did not overlook the basic inspection, which was great. And she didn’t mind when I checked everything myself.  Engine oil and coolant level were confirmed correct; whilst hoses, brackets, harness routing and engine mounts were all checked for security, interference or fouling with the chassis.

 

 She did all these things but understood that I had to do them myself—for my own peace of mind. 
The shop tried to resettle the engine mounts but it didn’t affect the vibration. It has been my experience that oftentimes, an idle vibration caused by ground-out within an engine mount can turned off/on with a single bolt location – shimming that bolt location may greatly cut back the vibration. In some cases, a combination of bolt location shimming may be needed.
We managed to get it down to 2.6 mg, using mild steel spacer washers, and then road-tested the vehicle. The customer was satisfied.
Linda wasn’t aware of GM PI documents, and I showed the one we worked off of.

“I learned some things from you today, RJ. Thank you so much.”

Western Star

The 2012 Western Star 4900 Series with a Detroit Diesel Series 60 originally had a SPN 524/FMI 9 DTC stored, indicating a J1939 ETC2 Message Missing. The technicians working on this truck checked for proper CPC configuration, ultimately replacing the CPC, because it failed to download MCM static fault data. After that, an SPN 630/FMI 14 Code flagged.

This code indicated that the CPC failed to download MCM static fault data and the repair is to reprogram the CPC with the latest software release. “After we did that, we ended up with an inconsistent static fault code data, reported by the MCM,” a very frustrated Dave Gordon, the technician, said. “I reprogrammed the MCM with the latest software,” he said. It was after that, the SPN 625 FMI 9 code set—abnormal data update rate.

When I got to the shop, it was in a pole barn, well-equipped and well-lit. I performed all the basic checks: battery connections and battery state of charge; fuses, grounds—I found a bad ground at the CPC. Once we eliminated the bad ground, I took out my ancient AM pocket radio. The shop was filled with interference. I once found interference coming from the rain gutters of an old barn. The farmer used a ladder to get up to the loft, and when he grabbed the rain gutter for support, he screamed from an electric shock. The interference on my AM radio stopped. He came down the ladder, still shaking, and asked me if it could be connected to a problem he was having when touching the metal sink in the barn or the refrigerator. It was.

Getting back to the pole barn/truck shop: Electromagnetic Interference is caused by one device inducing voltage (generating a discrete voltage without a direct electrical connection) within a second component.  Induced voltage occurs when devices are not properly shielded, are laid out improperly (e.g. coiled around objects or run parallel for the entire distance), use high frequency AC voltage, or are grounded improperly.

His shop lights used electronic ballasts.  Because ballasts typically generate a humming or buzzing noise – electronic ballasts are quieter than traditional magnetic ballasts, but the hum still exists – remotely mounted ballasts are sometimes preferred, which is what Allman had in his shop. Remotely installed electronic ballasts generate substantial amounts of EMI due to their higher operating frequencies (magnetic ballasts operate at 60 Hz while electronic ballasts are typically operated at 20-60 KHz, that’s 50 to 200 times greater). 

 If the connection cables are unshielded, the high frequency will convert the cables into a powerful antenna, creating an electromagnetic field that can affect radios, Wi-Fi connections, and cell signals.  In a fluorescent system, the fluorescent lamp itself is capable of radiating electromagnetic waves at frequencies of 10 KHz to 100 MHz depending on the electronic ballast connected to it.

Allman’s top technician, Dave, was attempting to program the truck’s ECU’s in the presence of all that EMI.

“So, how can you eliminate EMI?” Allman asked.

“Ensuring proper ground connections for all electrical devices will shunt high frequency interference to an earth ground or common, for starters,” I said.  If grounding is not done properly, cables, grounds, or electrical equipment can act as a very powerful antenna, radiating out a strong EM field.  “Grounding the fixture and ballast to a common earth ground will help prevent this from occurring.”

“We do a lot of programming,” Dave said.

“Cable runs should be placed in metal conduits, and fluorescent or HID lights can be housed in luminaires with copper mesh or conductive glass to shield against EMI generated by the cables or lamps.”

I also mentioned that all exposed conductors should be shielded.  The conductive material of the shielding will absorb the EM field and prevent radiated or conducted EMI.

Allman vowed to get the EMI down to manageable levels in his shop. With the Western Star’s ECUs properly programmed (without interference), the problems were resolved.