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The Sea Gull EffectPosted 7/9/1999By Jeff Bach
The Sea Gull Effect, which I often refer to as the Gull Effect, is a result of mechanical movement of an inductor through a magnetic field. This phenomenon has very important diagnostic implications. By observing the Gull Effect you can draw certain conclusions about the mechanical movement of a particular solenoid, relay, injector, etc. Usually the circuit will have about 20 percent to 40 percent more current than is necessary to pull in the coil so you will see the Gull about 2/3 to 3/4 of the way up the ramp. The size and distinction are directly related to the amount of movement. An injector pintle for example has a relatively limited amount of travel compared to that of an A/C clutch coil. The actual mechanical movement in the fuel injector (Figure 1) takes place in about 1/2 of 1 millisecond. Compare that to the 5 milliseconds an A/C clutch requires to complete its travel. To better illustrate the Gull Effect phenomenon, I will use a simple relay. A relay coil has a multitude of windings that electrons must pass through before completing a circuit. As you know, magnetic lines of force are created around the conductor as they go. The lines cut across the adjacent windings causing their electrons to move in opposition to the main flow. This is called Counter Electromotive Force (CEMF). When an inductor is placed in the core of a coil, the magnetic lines of force are attracted to the inductor; as current flows, they concentrate on it causing more CEMF and slow current build-up in the coil. Then as the magnetic field builds enough strength to pull in the inductor, a fluctuation occurs causing the current flow to lessen momentarily as the inductor moves through its travel to a stop. This is where you see the Gull Effect. After saturating the coil, the current will gradually reach a peak. I removed the inductor core and the contact bar from a relay and left only the coil bobbin for this demonstration (Figure 2). Then I installed the inductor into the relay core and took this image. (Figure 3) Note that the angle of the curve has decreased as the current build-up has slowed down. Figure 4 shows the relay fully assembled and working, demonstrating the full Gull Effect as the contact bar pulls in. Here the contact bar acts as another inductor further slowing the current build-up and changing the waveform as the bar moves. Stacking all three waveforms exemplifies the change the of inductive curve. (Figure 5) Figures 6, 7, 8 and 9 demonstrate another illustration of the effects of mechanical movement on the Gull Effect. This waveform (Figure 6) came from a Ford A/C compressor clutch coil circuit. The customer's complaint was that the car would not cool at times, usually when idling in traffic. It didn't take long to realize that an inoperative compressor clutch circuit was causing this condition. Above idle, the problem was not evident, but when allowing the car to idle for a few minutes, the compressor would stop engaging. The current waveform verifies the completion of the circuit, virtually eliminating the need to test the power circuit including cycling switch, the high pressure circuit, low pressure cut out, WOT cut out, ignition switch and the ground circuits. Above idle, when the compressor would engage (Figure 7) the Gull Effect was very evident due to the large magnetic field. It was the only thing missing from the circuit when the clutch failed to engage. The image in Figure 7 was my result after nudging the clutch plate with a piece of heater hose while my partner, Eric, cycled the switch. I removed a couple of shims to narrow the clutch gap to within spec (Figure 8). Observing the stacked waveforms is the best way to see my Gull Effect theory (Figure 9). The only thing different in these two waveforms is that the clutch gap is narrowed by .040 of an inch, causing the clutch to kick in 5 milliseconds sooner. PCM Pulse Width Modulated solenoids show their effects in varying degrees of duty cycle. This '96 Chevy Blazer EGR solenoid (Figure 10) is running at 10 percent duty cycle. Then 6.3 milliseconds later (Figure 11), it is at 20 percent duty cycle and the full Gull Effect can be seen. At 30 percent duty cycle (Figure 12), we have reached near-peak current. In Figure 13 you can see the solenoid current reading consistently throughout its range up to 50 percent duty cycle along with the voltage signals. At 100 percent duty cycle there would be a 63 mS pulse. There is a wealth of information contained in the current waveform. This next example further illustrates this point. This car came to me after several attempts to repair it by the owner and two other shops' efforts had proved futile. The car had a multitude of parts thrown at it, including an ECM, an IAC motor, a set of plugs, new plug wires, a fuel pump, a new ignition module, and the injectors cleaned. The car was stalling at stops hot, and lacked power on take off and going up hills. Once the car was dropped in my care, I began going about collecting the usual fuel pump, ignition and injector waveforms. I then took the car on a test drive. Nothing showed up with the tests and no performance problem was evident. Upon returning to the shop, I called the customer for another briefing to see if I could find out when the problem was most likely to occur. The owner just said, "Oh just keep driving. Once it starts it will do it every time. You may have to go about 20 miles or so. Then when you come to a stop, it feels like an old John Deer tractor." "Well why didn't you say that in the first place?" I thought to myself. Now I have a whole different feeling for this problem. I'm thinking it may be TCC related. I get a fresh battery for my Fluke 99 and grab my CRT current probe and hook it to the purple TCC sol wire at the brake switch. I start storing waveforms about every two miles until I start seeing them change. After about 10 miles of driving and touching the brake pedal kicking the TCC circuit in and out, I notice the Gull starts to diminish. Another two miles and the Gull disappears completely. I pull to the side and stop. Car still doesn't stall so I take off again, only now I start to feel that doggy, not-much-converter-action feel these cars get when the TCC solenoid sticks. After another mile or two, I get some more waves with no Gulls and try another stop. Bang! Bang! Bang! Bang! Conk! Conk! Conk! ... dead. Felt just like an old 1-cylinder John Deer on the last puff before it quit. Figure 14 shows the sequence in rainbow format. When I called the owner to tell him we had found his problem he asked, "What was is it, a mouse in the machine?" I said, "No, you're missing a bird, and that makes it a dog." I showed him the picture and explained the Gull Effect to him and told him to take it to a transmission shop to have the TCC solenoid replaced since we don't do that kind of work. He called me later that afternoon to say the trans shop he had talked to told him the TCC solenoid was not the problem. They said there was a change in the valve body that had to be made and they wouldn't do it unless he went for a complete overhaul. (Our industry had once again earned its reputation.) I should have sent the waveform with him. I called a friend of mine who owns a transmission shop and told them what we had found. I had previously shown this trans shop owner several other bad TCC solenoids' Sea Gulls that we have found. They replaced the solenoid and cured this problem. Mr. Kinder stopped by the shop a few days later to assure me that the problem was gone and tell me when he picked up his car at the trans shop, the guy showed him a part and called it "Bach's bad bird." Then he asked if he could have a copy of the rainbow picture that I had previously shown him. I was so busy the day we worked on his car, I had forgotten the most important thing. Using this current probe to find Sea Gulls reminds me of my Highlights days. Who says you can't have fun at work?
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