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Experience:  Ford Senior Master certified Tech, 36 years Ford technician.
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98 ford contour: rebuilt..tranny..cruising speeds it will jump in rpms

Customer Question

Ok i have a 98 ford contour with a 2.5 auto with a rebuilt tranny and new torque converter, when I drive down the road and get to cruising speeds it will jump in rpms then shift almost like its going in and out of gear. it is very random and there is no patterns, It does shift smooth otherwise. Ive looked and there are no wires loose under my brake that would knock the torque converter out, it seems like its more prone to doing on a bumpier road. it will do it in cruise and will not knock it out of cruise when its going through its spell, I had it at a shop to get a trans scan but no codes came up, I dont think he brought up a history though. The fluid is good, I just checked the other day and it seemed like it may be a little high. I bought the car 3 weeks ago. The overdrive light does not come on and off when the car studders either, I know its an electrical based tranny and would like to get an idea on which sensor to try first and if there is any good way test them.
Submitted: 5 years ago.
Category: Ford
Expert:  Brian replied 5 years ago.
I believe your assumption on an electrical problem is probably the most likely cause. The most common sensor that can fail and cause this symptom is the trans range sensor, it's what used to be called the nuetral safety switch. It sends a signal to the computer according to what gear position the shifter is in and controls the shifts accordingly, it also uses other sensors as inputs too. If the trans range sensor changes voltage, even slightly, without the shifter being moved it can cause it to downshift, and it won't set a fault code because as far as the computer knows, the shifter may have been moved to select a lower gear. This may be very difficult to test because in order for it to be out spec, it would have to fail, and it seems as if it is very intermitant, and you would have to be checking the sensor voltage when the fault occurs. The sensor is not very expensive, but it is a little difficult to get to to replace, there is a special tool that is used to line in up when you bolt it on.
SECTION 307-01: Automatic Transmission/Transaxle1998 Contour/Mystique Workshop Manual
IN-VEHICLE REPAIRProcedure revision date: 09/14/2001

Transmission Range (TR) Sensor


Special Tool(s)
TRS Alignment Tool
307-351 (T97L-70010-A)

Removal

  1. CAUTION: Disconnect the battery ground cable.

    Place the vehicle in NEUTRAL.
  1. Remove the battery tray. For additional information, refer to Section 414-01.
  1. Remove the transmission range (TR) sensor.
    1. Disconnect the TR electrical connector.
    1. Remove the bolts.
    1. Remove the TR sensor.

Installation

  1. NOTE: Make sure the transaxle is in the NEUTRAL position.

    Position the transmission range (TR) sensor and loosely install the bolts.
  1. NOTE: As necessary, move the manual control lever to N position for TR sensor adjustment.

    Rotate the manual valve detent lever assembly to the NEUTRAL position.
    1. Low 1
    1. Low 2
    1. Drive
    1. Neutral
    1. Reverse
    1. Park
  1. Install the TR sensor.
    • Using the special tool, align the TR sensor.
    • Tighten the bolts and remove the special tool.
    • Connect the electrical connector.
  1. Install the battery tray. For additional information, refer to Section 414-01.
  1. NOTE: When the battery has been disconnected and reconnected, some abnormal drive symptoms may occur while the vehicle relearns its adaptive strategy. The vehicle may need to be driven 16 Km (10 miles) or more to relearn the strategy.

    Connect the battery ground cable.
  1. Check the correct operation with the parking brake control engaged. The engine should start only in PARK or NEUTRAL. Backup lamps should be active only in the REVERSE position.


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