If, as you say, decelerating down a long hill triggers a full rich condition, bingo, you have a problem in your idle/WOT switches or in the circuitry. That's what I suspected some time ago when you posted about mpg problems. What I would do is, first, set the idle switch per Bentley. Move it back and forth several times with your light on it to see if it retains the setting. If it does not, replace the switch. Then, pull the ECU connector and do the pin test, again following Bentley. When testing pin 4, first actuate the throttle from idle to WOT, and then try to simulate engine vibrations by pushing the switches and wires back and forth, messing with them, to try to see if they're only working part of the time. That will test the switches and circuit together. If it operates erratically, replace switch and do what you need to fix the circuit. What makes me suspect the idle switch (or circuit) is that you say it swings to lean when exiting a freeway (normal) but doesn't do the same thing on long downhills. Both conditions should be the same, although I seem to remember mine swinging back from far left (lean) to near center after a period of long deceleration. I also have an '84 with two switches and know from experience how important they are. In any event, under no circumstances should the ECU be saying "rich" during deceleration. If in fact you are running rich on deceleration, that also accounts for at least part of your poor mpg. The engine will run fine, it just burns way more gas than it needs. The more you decelerate, the more important this becomes. |
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