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Oxygen Sensor DesignPosted 5/12/1998By Bill Sauer, AAM
Recently, I've been asked about the difference between oxygen sensors? Since all zirconia sensors do the same thing, why aren't they universal? There is the one-wire, two-wire, etc., but what's the difference in the sensor itself? Why can't it be interchangeable? Here's what I found: On 1988 and newer engine management systems, the pilot programming in the PCM has a degradation factor built in as it relates to response time. It then makes up for the degradation with an increased frequency. There is also a built-in algorithm to change pulse width. Example: If a sensor gave a full-rich voltage of 9.6 when it was new, but degraded to 8.5, the PCM expects that and will compensate for it. So, if you replace the original sensor with one that has a different degradation factor, the calibration factor of the PCM is off. What affects this degradation factor is called the spinell layer. This is a layer that is sprayed onto the zirconia to protect it from the abrasive materials in the exhaust stream. Bosch and AC Delco sensors are quite the same, so interchangeability is quite compatible. However, the Japanese sensors (such as NGK and NIP) have unique manufacturing processes. Their spinell layer is tighter so they "plug up" sooner, which slows down the sensor's response time. What it boils down to is the microporosity of the spinell layer. The number and design of the slits are also a big factor. Ever wonder why some sensors have only two slits and some have many, or a bunch of holes? The number of slits and the microporosity of the spinell layer go hand in hand. For example, on a turbocharged engine there are only two slits because of the rush of the exhaust. You can see if you had one with a lot of slits in a turbo engine, it would tend to erode the spinell layer faster, but with just a few slits the layer is protected. The reverse is true - on a non-turbo engine, if the sensor is replaced with one with few slits, there is not enough exposure to the zirconia. It would certainly protect the spinell layer, but not produce enough exhaust to get accurate readings. Ford engines are especially sensitive to the number of slits. Also, the placement of the O2 sensor - the distance away from the exhaust valve - is critical. The closer the sensor is, the fewer the amount of slits the sensor will have to decrease the amount of heat the spinell layer will see. Sensors in the manifold will have only a few slits and sensors further downstream will have more slits or holes. Some sensors have slits that face clockwise, others face counterclockwise. When replacing the sensor, be sure the slits are faced in the proper direction or exhaust flow into the sensor will be changed. You can see, too, that all this is much more sensitive and important on OBD-II engines. So when it comes to oxygen sensors, there isn't a generic "one size fits all." Be conscientious and watch the application ... it can save you a comeback. Thanks to Pete Sullivan of Progressive Diagnostics in Bellaire, Texas, for supplying background information for this article.
Hondas - Give 'Em a Brake!Posted 5/12/1998By Marlowe Peterson
When servicing brakes on any car, it's not only important to replace what wears out, lube what needs lubricating, and service what needs servicing, but it's also important to know exactly what you're servicing and how it's supposed to work. Many problems can show up on Hondas because the rear brakes aren't serviced correctly. The most common mistake is the adjustment of the emergency brake in relationship to the rear brake star adjusters. Always make sure the emergency brake adjustment is backed off all the way before adjusting the rear brakes. At the rear of the center console, a cover can be popped out with your pocket screwdriver. Below that pocket is the emergency brake adjusting nut. Back that nut off so no threads of the cable are exposed, but the nut is still attached. Then make sure the emergency brake link is backed off on both sides and that the emergency brake cable is not rusted or binding in its sheathing. Adjust the star adjuster on the rear brakes. With the drums back on and the rear brakes adjusted properly, engage the emergency brake to make sure it applies. Adjust the nut if necessary so the emergency brake is fully applied with seven to 11 clicks. On Prelude models with rear disc brakes, the emergency brake cable attaches to a lever on the caliper. If this lever does not return fully to its rest position (a post stops the lever), the rear brakes will not adjust. Make sure the lever has free movement and that the cables are free in this application - or the result will be a low pedal. If you have any questions on Honda brakes, just give me a call.
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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