1987 Fleetwood FWD TPS and ISC problems
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 1987 Fleetwood FWD TPS and ISC problems in Past Cadillac Vehicle Discussion; I have a 1987 Fleetwood 4.1 replaced the TPS and it worked fine. Then went back to e26,27. My ECM ...
  1. #1
    mobilethom's Avatar
    mobilethom is offline Cadillac Owners Member
    Automobile(s): 1987 Fleetwood de'elegance
    Join Date
    Jan 2013
    Location
    Oceanside, CA
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    52
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    Lightbulb 1987 Fleetwood FWD TPS and ISC problems

    I have a 1987 Fleetwood 4.1 replaced the TPS and it worked fine. Then went back to e26,27. My ECM was displaying .01 on P0.1. Now is displaying 32.0 and won't go lower than 28. or so I Set the ISC (retracted) to .060 then tried to set the TPS. I haven't tested the ISC. Does anyone have the service manual or at least the section regarding the TPS and ISC? Please e-mail me at mobilethom@aol.com or call me 760-681-3420. I really need HELP.

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  3. #2
    limo1 is offline Cadillac Owners Member
    Automobile(s): 1985 Fleetwood 75
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    Jul 2012
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    Re: 1987 Cadillac Fleetwood FWD TPS and ISC problems ~ Please HELP

    There should be 3 wires on the plug into the TPS sensor one is ground second is the variable output last it the 5V reference. Confirm you have 5V between the ground wire and the 5V ref wire. Also measure the variable output wire as you are adjusting the throttle plate voltage should go from about 0.5V up to 5V wide open throttle. if you do not get 5V on the Ref wire check for shorts or open wiring harness all the way back to the motor ECM pin 5V output. also this 5V ref supplies other sensors confirm they are not shorting to ground or the ECM 5V output is not working. also confirm the plug into ECM is not corroded. Unplug and clean the connections.
    If you get the correct voltages make the TPS adjustment to throttle stop with the ISC fully retracted and confirm the throttle plate is back against the set screw in the carb and not being stopped by the ISC shaft. Motor should idle about 450 to 500 RPM
    Adjust the TPS sensor by loosening two screws and turn until you have 0.5V output on the TPS variable output Pin, as well as confirm that 5V is going into the REF pin. also on the display P01 it should show 0
    As the throttle is openned the P01 should vary from 0 up to about 80 this being wide open throttle. Reconnect ISC and it should adjust the throttle to maintain about 600 RPM on motor when running.
    Also if AC is engaged you should see the ISC motor extend slightly before compressor engages.
    If all this works confirm the idle switch inside the ISC motor is engaging when the shaft is retracted. this switch can go open and not work causing ECM to vary the ISC motor and not know where to park the ISC plunger.
    ISC idle switch is a micro switch inside the ISC motor and it can have problems. There are four wires into the ISC motor two are the motor drive and two are the micro switch contacts.
    Confirm when no accelerate pedal is pushed that the ISC idle switch is engaged it should show up as an output on the dash when ecm is in diagnostic mode. As you push the peddle slightly the indication will go out confirming peddle is depressed.

  4. #3
    mobilethom's Avatar
    mobilethom is offline Cadillac Owners Member
    Automobile(s): 1987 Fleetwood de'elegance
    Join Date
    Jan 2013
    Location
    Oceanside, CA
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    52
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    3

    Re: 1987 Fleetwood FWD TPS and ISC problems

    I replaced the TPS and set it P.0.1 as close to 0 as I could. then the error codes E26,27 went away as well as the check engine light in the dash. The next time I started the car it went back to the same errors. Then I replaced the pigtail connector on the TPS and tried to set it to 0 deg P.0.1 and it won't go below 23 deg and the voltage won't gpo below 1.5V or so??? Can the ISC cause these problems with the TPS? Please call me if you can help 760-681-3420 or e-mail me at tjwatermeier@us-toner.com.

    Best regards,

    Thomas

  5. #4
    limo1 is offline Cadillac Owners Member
    Automobile(s): 1985 Fleetwood 75
    Join Date
    Jul 2012
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    Re: 1987 Fleetwood FWD TPS and ISC problems

    Do a resistance test on the TPS sender, remove the plug and measure ohms between the center pin and one outside pin when plate is fully open or closed should almost get 0 ohms when throttle plate is rotated the resistance will increase or decrease depending on pins measured. Measure resistance between two outside pins total should be around 5kohms. when moving throttle plate the resistances should go up or down smoothly.

    The ISC motor idle switch should not affect the TPS sensor. However if ISC extends during start and does not retract back slowly after start it will hold plate open.
    Remove the ISC motor off the carb and confirm the throttle plate is hitting the stop screw. could be possible the throttle plate is binding on something and not hitting the stop screw. also re install the TPS sensor onto the carb and confirm the small tab is on the correct side to the throttler shaft actuator. it could be binding.
    During start the ISC shaft should extend then slowly retract. If however the motor is not retracting the ISC motor should be checked for binding
    I would replace the ISC motor as the bearings are plastic and this motor wears out over time and can operate one direction then bind going backwards.

    If TPS is ok and no water got into it next test the wiring back to the ECM is there any dirty connectors or shorted wire to ground. I believe there is a test connector in the wiring harness confirm this is not shorted to ground. It can be used to measure voltage when operating the throttle plate. Last check the ECM connecter remove the connector clean the contacts into the ECM and confirm no pinched wires or corrosion. It could also be possible a 12V got onto the TPS sense wire and popped the ECM protection input circuits. the plug is for measurement test only however someone may have applied 12V to it thinking is was part of the fuel pump priming connector.

  6. #5
    mobilethom's Avatar
    mobilethom is offline Cadillac Owners Member
    Automobile(s): 1987 Fleetwood de'elegance
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    Thumbs up Re: 1987 Fleetwood FWD TPS and ISC problems

    Quote Originally Posted by limo1 View Post
    Do a resistance test on the TPS sender, remove the plug and measure ohms between the center pin and one outside pin when plate is fully open or closed should almost get 0 ohms when throttle plate is rotated the resistance will increase or decrease depending on pins measured. Measure resistance between two outside pins total should be around 5kohms. when moving throttle plate the resistances should go up or down smoothly.

    The ISC motor idle switch should not affect the TPS sensor. However if ISC extends during start and does not retract back slowly after start it will hold plate open.
    Remove the ISC motor off the carb and confirm the throttle plate is hitting the stop screw. could be possible the throttle plate is binding on something and not hitting the stop screw. also re install the TPS sensor onto the carb and confirm the small tab is on the correct side to the throttler shaft actuator. it could be binding.
    During start the ISC shaft should extend then slowly retract. If however the motor is not retracting the ISC motor should be checked for binding
    I would replace the ISC motor as the bearings are plastic and this motor wears out over time and can operate one direction then bind going backwards.

    If TPS is ok and no water got into it next test the wiring back to the ECM is there any dirty connectors or shorted wire to ground. I believe there is a test connector in the wiring harness confirm this is not shorted to ground. It can be used to measure voltage when operating the throttle plate. Last check the ECM connecter remove the connector clean the contacts into the ECM and confirm no pinched wires or corrosion. It could also be possible a 12V got onto the TPS sense wire and popped the ECM protection input circuits. the plug is for measurement test only however someone may have applied 12V to it thinking is was part of the fuel pump priming connector.

    Dear Limo,
    You are awesome! Thank you so much for your threads. If the 12VDC was applied do I have to replace ECM? The voltage on the TPS is 1.0+VDC and the P.0.1 is 25 degrees and above? ECM?

    Best regards,

    Thomas

  7. #6
    limo1 is offline Cadillac Owners Member
    Automobile(s): 1985 Fleetwood 75
    Join Date
    Jul 2012
    Posts
    97

    Re: 1987 Fleetwood FWD TPS and ISC problems

    The ECM can be opened up and check the 5V output transistors for short. also when you are in there you can replace the quad output driver IC on the output board as the original IC were not output protected and would blow from the back EMF from coils or bad connections. best way is to put diodes onto all the control air switches to block back EMF getting into the ECM.
    Part use for quad driver replacement UDN2559BT
    Description IC DRIVER QUAD PROTECTED 16DIP
    These IC's in ECM pop from reverse EMF from fuel pump relay, TCC lockup I think Air bypass, EVAP relay etc.
    if you just replace the ECM with Reman you may just get a unit that will pop again if you have a faulty coil or bad connection
    ECM can be fixed as it is older tech with a IO board, CPU board. the board with the transistors on the heat sink has the two for the dual outputs to the injector drives also there is an IC for the ISC motor.
    there will be a transistor for the 5V regulated supply measure the diode junctions for the .7V across the E-B and C-B if popped replace the part a couple bucks.
    it is like working on an old IBM AT computer

    Also it is possible a sensor is shorting to ground and pulling the 5V supply down you say about 1V check other sensors. a blown 5V ref should go to 0V.
    temp sensor, IAT sensor
    pull the ECM connector and confirm resistance to ground for the TPS 5V side it may be shorting to ground somewhere in the motor or harness.
    also the transmission has a sensor UN plug it see if it goes to 5V on the TPS . transmission has a temp sensor inside and compares it with a resistor in the harness could be shorted from heat
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