Motor Age Garage: Resonation Diagnostics

Having a game plan and the proper equipment is very crucial to diagnosing modern vehicles. It is like an all-out war: You against the vehicle. But in this war, there are no prisoners taken. The only thing that you take to the next battle is the exper
Jan. 1, 2020
7 min read

The diagnostic approach a technician takes should be well thought out. When done properly, a technician will choose the proper test(s) that can shorten diagnostic time.

Having a game plan and the proper equipment is very crucial to diagnosing modern vehicles. It is like an all-out war: You against the vehicle. But in this war, there are no prisoners taken. The only thing that you take to the next battle is the experience of winning or losing, and if you lose, your training and integrity get hit below the belt.

The most important thing in repairing modern vehicles is understanding vehicle computer strategies: How a particular part you are testing functions, or how on-board computer systems decide to control those parts. You cannot test a device if you do not know how it functions.

I am a mobile technician who is hired to resolve problems with a vehicle that may be out of the scope of an average garage technician. At times, they lack knowledge of a particular system or do not have the proper tool to perform a task. A technician's knowledge is based on the shop's emphasis on continuing education and staying in the automotive loop. Having the right tools available means keeping test equipment up-to-date and providing a wide variety of service information systems that help diagnose vehicles.

DIAGNOSIS MISFIRE

VEHICLE: 1998 Ford E250 DRIVETRAIN: 5.4-liter Triton engine MILEAGE: 78,543 COMPLAINT: Multiple misfires.

I was called in to diagnose a problem vehicle, a 1998 Ford E250 with a 5.4-liter Triton engine. This Triton didn't have the power of the god it was named after. It appeared to be missing on multiple cylinders. After spending hours of diagnostic time, the shop's owner thought the problem might be the coils, but he had no way of checking it. If he was not a conscientious shop owner, he might have tried replacing all eight ignition coils, which would have been an expensive guess.

During my initial diagnosis, I noticed the "Check Engine" light was flashing. This would confirm the presence of a misfire and could be an indication that the catalytic converter would be damaged if the engine was allowed to run.

My game plan started with my scanner. I checked the diagnostic codes and found a P0300 stored in memory. I checked the scan tool data, but there were no clues in the data stream. On Fords, the misfire monitor is a continuous monitor; however, Ford displays this data in Mode $06. Mode $06 displays the results of on-board diagnostic monitoring tests of specific components and systems that are not continuously monitored. Because Mode $06 contains the misfire data, I investigated. But no one cylinder or cylinders stood out as faulty.

The scanner allows the technician to gather a large amount of data very quickly. Analyzing this data, the technician can then determine a diagnostic direction. The diagnostic approach a technician takes should be well thought out. When done properly, a technician will choose the proper test(s) that can shorten diagnostic time.

To check the cylinder misfire, my choice was to connect my analyzer, which is an eight-channel oscilloscope. With this tool, I can view all eight ignition primary waveforms at the same time. A good ignition analyzer will help the technician pinpoint emission and drivability problems. Keep in mind that this engine has very little room for performing certain tasks.

Hooking up a coil-on-plug (COP) adapter to check coil secondary involves removing a coil, which takes a lot of time and could easily eliminate carbon tracking to the spark plug housing or cylinder head. This could have caused the technician to miss the problem with the vehicle. Placing non-intrusive COP adapters on each coil has noise and accuracy issues associated with it, and it is not an easy job on this engine, especially when the engine compartment has reached more than 400°F.

The quickest and easiest place to go is the Powertrain Control Module (PCM), which is accessible at the firewall near the brake booster. By using the engine performance wiring diagram, I connected my eight-trace oscilloscope to each of the control circuits for the ignition primary signals. On the Triton engine, the top and bottom rows of wires at the PCM connector are the injector coil drivers. See Figure 2.
When viewing the coil primary patterns, I saw the coil secondary resonating in the waveform. The key is to change the scope's time base to stretch out the patterns, allowing you to view details in the waveform. But looking at all eight primary signals at once on a typical Triton V8 does not provide you with the resolution you need to perform this task. See Figure 3.
My scope has the ability to flow the patterns into an engine analyzer program, and it provides eight individual triggers that will stack or superimpose on the patterns. By simply stacking the patterns or superimposing the signals on this vehicle, you can now visually associate and compare all the signals to one another. See Figures 4 and 5. You don't have to be a rocket scientist to figure out which cylinders are faulty; you only need to remember which color scope leads are hooked up to which primary circuits.
The problem cylinders in this Triton can be seen as Red (CH2), Purple (CH6) and Brown (CH8). They all lack cylinder turbulence in the spark line indicating a lack of cylinder activity. Also notice the Red trace's fire line starting at about 6 kilovolts (kV) and sloping downward. The burn time is shorter, but the first oscillation downward after the burn time is quite small, indicating that the coil has discharged most of its energy. This could be an indication of a fouled spark plug.
Going back to the wiring diagram, I found that the Red lead was on cylinder 7, the Purple lead on cylinder 1 and my Brown lead on cylinder 4. Removing the spark plugs revealed that cylinder 7 (first in order; see Figure 6) was misfiring because of a lack of kilovolts that were shorting to ground through the spark plug boot of the ignition coil. See Figure 7.
Cylinders 1 and 4 had spark plugs that were wet with oil and fuel and were not firing at all. I decided to do a compression check on all three cylinders to be on the safe side. Taking a compression reading showed good compression at 160 psi in six cylinders. See Figure 8. But two cylinders showed no compression at all. See Figure 9.
I then performed a cylinder leak down test that showed the valves were leaking. After checking the technical service bulletins on this Triton motor, I found that extensive carbon on the valve stem had been causing compression problems. The fix here was to perform a complete tune-up and a carbon treatment on the Triton.
Using ignition waveforms to gather diagnostic information is a valuable tool to shorten your diagnostic time. Having the use of a multiple trace scope is the key factor. When using a four-trace scope, you have to split the firing order in half and scope the first four cylinders in the firing order to see pattern detail once the time base is spread out. This is just another way of beating the odds with COP technology.
The real winner here was the shop owner. Had he replaced all eight coils, there still would have been unresolved problems. Knowledge of the system and use of the right tools led to a quick, accurate diagnosis of this Triton engine. Once we were done with the repairs, the Triton once again had the power of the god for which is was named.

JOHN ANELLO is the owner and operator of Tech On Wheels, a mobile diagnostic service for mechanical and collision repair shops. An ASE-certified Master Technician since 1979, he also freelances as a technical trainer and writer and authored the book "Automotive Computer Diagnostics."

About the Author

John Anello

John Anello

Owner and operator of Auto Tech on Wheels

John Anello is the owner and operator of Auto Tech on Wheels, established in 1991 in northern New Jersey. He provides technical assistance and remote reprogramming with 21 factory PC-based scan tools. Driven by a passion for cars, John's business now services roughly 1,700 shops.

Sign up for our eNewsletters
Get the latest news and updates

Related

Calibration Crisis: How Drivers' Safety May Be Placed at Risk
Financial Series: Optimizing Paint and Material and Sublet Gross Profit
ADAS Applications: What They Are & What They Do
Sponsored
The Autel IA700: Advanced Modular ADAS is Here
Sponsored