Question about Lincoln Town Car

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96 tc surges under med to heavy load between 30-50mph have had it checked and cleared for possible tran. and fuel problems car has 103k,engine35k what might it be ? thanks

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  • daeweee1 Mar 14, 2011

    no!

  • daeweee1 Mar 14, 2011

    no engine light on!

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  • Lincoln Master
  • 7,716 Answers

Hi, there are several components that can affect the injector pulse width, which is causing the surge. The best way to diagnose this is to hook up a scanner and drive the car while someone looks at the data. The data to check is the upstream oxygen sensors, MAP sensor, throttle position sensor (if you have one), and the mass airflow sensor. These are the components that have the largest potential to cause a surge. If the car cannot be scanned under load, these compnents will need to be tested individually to determine which is at fault. Another possible sorce for help with the diagnosis is if the computer has set the engine light. In that case, the scanner can extract trouble codes that may also identify the problem component. Is the engine light on?

Posted on Mar 14, 2011

  • 2 more comments 
  • Jeff Turcotte
    Jeff Turcotte Mar 14, 2011

    OK, I'm going to look up some tests to run on the sensors for you. These will come in parts as I look them up. You don't need to look every time I post, but I should have them all posted within the next hour.

  • Jeff Turcotte
    Jeff Turcotte Mar 14, 2011

    Here are tests for the MAF sensor. By the way, it's a good idea to try cleaning your sensor with some spray electrical parts cleaner. Never touch the sensor with your hand or anything but a spray cleaner. The cost of a new MAF is $80-100. If you don't have the equipment to run a given test, just let me know. And also let me know if there is anything here you don't understand. This manual assumes you know how to test electrical components, but you may not. Don't be embarrassed to ask--that's what you're paying for.



    Testing









    Fig. TESTING the SIG circuit of the MAF sensor










    Fig. TESTING the VPWR circuit of the MAF sensor




    1. Using a multimeter, check for voltage by backprobing the MAF sensor connector.

    2. With the key ON, and the engine OFF, verify that there is at least 10.5 volts between the VPWR and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

    3. With the key ON, and the engine ON, verify that there is at least 4.5 volts between the SIG and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

    4. With the key ON, and the engine ON, check voltage between GND and SIG RTN terminals. Voltage should be approximately 0.34-1.96 volts. If voltage is not within specification, the sensor may be faulty.








    Fig. Unplugging the sensor connector below the MAF sensor, for testing purposes




    1. Using a multimeter, check for voltage by backprobing the MAF sensor connector.

    2. With the key ON , and the engine OFF , verify that there is at least 10.5 volts between the VPWR and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

    3. With the key ON , and the engine ON , verify that there is at least 4.5 volts between the SIG and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

    4. With the key ON , and the engine ON , check voltage between GND and SIG RTN terminals. Voltage should be approximately 0.34-1.96 volts. If voltage is not within specification, the sensor may be faulty.


    MAF Sensor Pin Testing





    NOTE

    For reference values, refer to PCM testing-PCM reference voltage chart




    This pinpoint test is intended to diagnose the following:


    Mass air flow sensor (12B579)

    Harness circuits: MAF SIG, MAF RTN, vehicle power (VPWR), power ground (PWRGND), IAT and SIGRTN





















  • Jeff Turcotte
    Jeff Turcotte Mar 14, 2011

    I have checked, and you don't have a MAP sensor. Therefore, the throttle position sensor is a primary input to the pulse width calculation. The sensor is mounted to the throttle body right at the throttle plate shaft. While there, check to make sure the throttle cable operates smoothly without binding and has a bit of slack when the accelerator is full up. All of the below tests should be run with the connector on the sensor. Probe the back of the connector to make contact with the pins/wires. Have your voltmeter negative probe connected to chassis or engine ground.









    Fig. TESTING the supply voltage at the TP sensor connector




    Fig. Testing the TP sensor signal return voltage at idle








    Fig. Test the operation of the TP sensor by gently opening the throttle while observing the signal return voltage. The voltage should move smoothly according to the amount the throttle is opened

    With the engine OFF and the ignition ON , check the voltage at the signal return circuit of the TP sensor by carefully backprobing the connector using a DVOM.




    1. Voltage should be between 0.2 and 1.4 volts at idle.

    2. Slowly move the throttle pulley to the wide-open throttle (WOT) position and watch the voltage on the DVOM. The voltage should slowly rise to slightly less than 4.8v at Wide Open Throttle (WOT).

    3. If no voltage is present, check the wiring harness for supply voltage (5.0v) and ground (0.3v or less), by referring to your corresponding wiring guide. If supply voltage and ground are present, but no output voltage from TP, replace the TP sensor. If supply voltage and ground do not meet specifications, make necessary repairs to the harness or PCM.

  • Jeff Turcotte
    Jeff Turcotte Mar 14, 2011

    The upstream oxygen sensors are mounted at the base the engine exhaust manifolds as shown below (#2 and #6). The sensor has a heating element and a sensing element. First test the heating element, then the sensor itself as indicated. Please let me know which of these tests you are able to accomplish. I have listed them in order of likelyhood to cause your symptom, so I recommend you start with the MAF sensor. If you find anything isn't working as specified, it's time to stop and correct that condition. Please let me know if you have any questions. I will be working in the field tomorrow, but I'll try to check my messages during the day.





    WARNING

    Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Backprobe the connector to properly read the voltage of the HO2S.



    Warm the engine to normal operating temperature.



    1. Disconnect the HO2S.

    2. Measure the resistance between PWR and GND terminals of the sensor. Resistance should be approximately 6 ohms at 68 °F (20 °C). If resistance is not within specification, the sensor's heater element is faulty.

    3. With the HO2S connected and engine running, measure the voltage with a Digital Volt-Ohmmeter (DVOM) between terminals HO2S and SIG RTN (GND) of the oxygen sensor connector. Voltage should fluctuate between 0.01 -1.0 volts. If voltage fluctuation is slow or voltage is not within specification, the sensor may be faulty.

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