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1997 Ford Thunderbird Question: NO FORD TECHS HAVE STEPPED UP YET.IT GOES INTO OPEN LOOP AFTER IT STARTS WARMING

 

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TOOLMAN57, 4.6L V8, Eugene, OR, September 16, 2012, 22:37
 Rookie

NO FORD TECHS HAVE STEPPED UP YET.IT GOES INTO OPEN LOOP AFTER IT STARTS WARMING UP.REPLACED COOLENT SENSOR NO CHANGE. THINKING MAYBE ECM/PCM.GOING TO ORDER MON.WHAT SHOULD TPS READING BE IN CLOSED LOOP? STILL SHOWING 18% AT ABOUT 960 RPM.AT COLD START.LONG TERM FUEL TRIM ALWAYS 0. THINKING PCM.IF ANYBODY ELSE WANTS TO JUMP IN HERE FEEL FREE. AGAIN THIS ENGINE RUNS GREAT UNTILL IT STARTS TO WARM UP.NO CODES ARE DETECTED UNTILL YOU RUN IT AT ABOUT 2000 RPM FOR ABOUT 5 MIN. THEN IT HAS THE O2 SWITCHING CODE.REPLACED TPS, IAC, MAF, ALL FOUR 02 SENSORS,REMOVED AND CLEANED THROTTLE BODY, CHECKED EGR, GOOD.IHAVE WATCHED THE SCANNER. IT GOES TO CLOSED LOOP THEN BACK TO OPEN LOOP AS SOON AS THIS HAPPENS IT STARTS RUNNING ROUGH AND RICH (BLACK SMOKE FROM TAILPIPE).

4 Answers
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  • Answer #1

    Greg's Orange Auto (12219 Answers) , Orange, CA - (714) 361-9355
    globalhelper September 17, 2012, 06:11
     Master

    is thermostat poss stuck open? what is coolant temp and air temp?

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  • Answer #2

    Chevy Power September 17, 2012, 07:20
     Journeyman

    Had a similar situation a few years ago and after 2 days I found the connector from the O2 sensor to the body harness was corroded and shorting when it heated up. The PCM uses the front O2 sensor and coolant temp. to go into closed loop. What is the "O2 switching code"?

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  • Answer #3

    ziptie12 September 17, 2012, 18:28
     Master

    18% for TPS is to high. Did you replace the temp sender for guage/light , or the sensor for the PCM ? Scan cold ECT temp. then watch as it warms up to verify funtion. Poss. wiring issue. Give code #s , and any 'freeze frame' data , that will also help.

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  • Answer #4

    dandd January 23, 2014, 11:29
    Profile_thumbnail
     Master

    I would check the real temperature of the engine with a lazer pyrometer, that way you will know the actual engine temp to see if the coolant temp sensor is telling you the truth. If the coolant temp and engine temp agree and are too low, say around 150-160 degrees, then replace your thermostat so your can get your engine into closed loop. Until your engine goes into closed loop, the fuel trim not be active and its reading will not make any sense. Fuel trim is an adjustment that is made by the PCM to keep the engine fuel control within a tight spec window, so the engine never runs too lean or too rich. Some call this stoichiometric fuel control. The PCM will add or subtract from the millisecond injector 'on time' which adds to or subtracts from, the amount of fuel delivered to the engine.

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