Tech To Tech
Do You Have A Strategy?
The first time you play poker it
seems you just can't win. As you master the rules, you get better.
Just when you think you've got a winning hand, a wild card beats
you. Your "friends" knew black one-eyed Jacks were wild,
but forgot to let you know. Frustrating? Sure. The same is true
in the world of computerized automobiles.
The secret "wild card" rules, stored in the car's on-board computer, are called strategies. Just when you learn how a feedback system responds to inputs, one of these wild cards throws you for a loop. I have been on a mission to have manufacturers publish these strategies. Manufacturers see this as proprietary information. Sometimes the programming represents a better method of control. Sometimes, however, the manufacturers are just too embarrassed to admit what they've done.
Let's lay the ground rules for automotive computer programming. Automobile manufacturers must produce vehicles that: pass the stringent Federal Test Procedure (FTP); maintain a Corporate Average Fuel Economy (CAFE) or pay a gas guzzler tax; and are powerful, smooth running and affordable to the general public. As you can see, many of these objectives are in direct conflict.
Ever cram for a test? Cramming is a technique used to get a grade, not retain knowledge. Cramming is cheating! You cheat yourself to achieve a grade. The grade becomes more important than the quest for knowledge. The same holds true for the FTP. The true goal is clean air. However, the FTP standard is so tough sometimes the goal is just to pass.
The Cadillac Case
Cadillac paid a record fine last
year for violating the Clean Air Act. The Cadillacs passed the
required test procedures and were certified for sale. Why the
fine? The guys at Cadillac are probably still asking that question.
The legal problem resulted from an interpretation of the intent of the law. The FTP is performed under specific conditions called "conditioning mode." Any condition other than this is called "off conditioning mode." Air conditioning on is an off conditioning mode. All cars are tested with the air conditioning off so the manufacturer can set the fuel mixture wherever they want with the A/C on.
Cadillac had trouble getting a smooth idle with the A/C on. Since increasing the idle speed can cause idle creep or banging when changing gears, Cadillac's solution was to use a rich fuel mixture with the A/C on. This strategy was perfectly legal at the time.
The EPA felt Cadillac did not follow the intent of the Clean Air Act. The dispute ended up in court and Cadillac lost. Perhaps Cadillac didn't defend itself too vigorously because it didn't want the government digging deeper into its strategies.
Cadillac recalled the affected cars to change the proms to a new calibration. Wrapping themselves in the environmental flag, the Cadillac spin doctors trumpeted how much money they spent on the recall because of their concern for the environment. Hey, I'm not singling these guys out, all manufacturers are guilty.
My 1984 Ford Van
In the early days, extreme heat generated
by catalytic converters sometimes caused fires. At a festival
north of Phoenix, Ariz., more than 400 cars went up in flames
after they were parked in a dry grass field. Burned carpet and
forest fires suddenly were a huge liability problem. So, how do
you deal with a hot converter?
The FTP's longest idle period is 30 seconds. After that, all bets are off. I tried to set the idle emissions on my Ford van with a 4.9L Feedback Controlled Carburetor (FBC) system. Every time I turned the idle screw to lean it out, the FBC solenoid signal drove it back to rich! What's a tech supposed to do? The O2 signal was stuck at .9 volts. The computer knew this was pig rich and didn't care! Some other signal with greater authority had control. I checked the MAP sensor and the CTS. All inputs were prefect. The computer wanted to do this!
Interestingly, if I blipped the throttle and the computer recognized a rapid change in the TPS and MAP, it would drop into closed loop at idle for about 60 seconds and pass! I also noticed a change in the air pump noise at the end of 60 seconds. The air pump switched from downstream air to the converter to bypass at the end of 60 seconds. Sooo, with the air turned off at the same time the computer commanded a rich mixture (5 percent CO), this was no defect. This was a strategy.
Going back to fire liability and 30-second idle time to pass the FTP, it became obvious what was happening. Turning the air off to the converter will help stop the catalytic action. Also ramping the fuel mixture to pig rich will deprive the converter of any O2 and the excess fuel will help cool the exhaust and converter. Hey, I passed the FTP without causing a fire! Clean air? Not this time.
Honda
Hondas failed the Arizona idle test
in the early days when we had idle-only testing. Carpet fires
occurred in the cramped spaces they worked in. Honda timers were
good for about a minute at idle, but only after a Vehicle Speed
Signal (VSS) was visible. After sitting in an emissions bay for
more than a minute, once again no air injection and pig rich until
a VSS signal was evident, you can see how a failed VSS could cause
a gross emissions failure.
Technical Service Bulletins (TSBs) later described specific procedures that differed from the complex and expensive FTP to get these vehicles to pass local emissions tests. The early Fords required turning off the ignition and restarting the testing idle within 30 seconds to reset the timer. Hondas required running past 25 mph on rollers to reset the timer to pass. To do a shop idle test, we had to test drive them, pull in and test fast.
You can see why manufacturers wouldn't want to publish some of these unclean air strategies. With converters causing fires, they were caught between a rock and a hard spot. You must understand these hidden agendas to prevent wasting time trying to fix a nonexistent problem.
The best solution for emission failures we have found is to turn off all loads and test drive the car monitoring the O2 sensor waveform. If the O2 sensor is sweeping well on a test drive and through the first 30 seconds of idle, then it should have no problem passing a valid emissions test.
Never underestimate the evil programmed into that computer! Never assume anything! Never ever say never!
Mechanical Repair In The Collision Shop ||
Remanufactured Engines: An Overlooked Alternative ||
Effective Communications In The Workplace ||
Service Selling And Customer Convenience
A Look At The 104th Congress || Classic Headache? ||
Guest Editorial: Coordinate Your Efforts For Optimal Results
Tech To Tech || TechTips || News Briefs || Taking The Hill
Directions || Around ASA || Chairman's Message
AutoInc. Magazine ®, Vol. XLIV No. 12, December 1996