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Tim's Auto Repair
Tim's Auto Repair, Mechanic
Category: Car
Satisfied Customers: 15926
Experience:  Have owned a repair shop for 25 yrs.
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I have a 94 oldsmobile regency. In the mornings my car cranks

Customer Question

I have a 94 oldsmobile regency. In the mornings my car cranks perfect. It also runs pretty good while driving. When I drive my car 'lets say for 30 min.' long enough for it warm up. I go to the store, cut it off come right back out and it cranks right up. But if it sets about 20 or 30 mins. it will not crank. I have to wait bout 15 mins. before it will crank. When it finally cranks the engine light comes on. If I drive the car with it on it runs really bad. But if I cut it off then right back on the check engine light goes off and the car runs great. Also, it will cut off while I'm driving and I have to do the same cycle over again. Thought it was fuel pump, bought a brand new one and ran great for a week then back to the same thing. You have any suggestions on what it could possibly be.
Submitted: 6 years ago.
Category: Car
Expert:  Tim's Auto Repair replied 6 years ago.


this sounds as if you may have a bad crank sensor...these will do this with heat sometimes when they go bad


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Crankshaft Position Sensor





See Figures 1, 2 and 3

The dual Crankshaft Position (CKP) sensor is mounted to the front of the engine, attached to an aluminum bracket mounted to the left side of the engine at the timing chain cover. A 4-wire connector plugs into the sensor, connecting it to the ignition control module. The CKP sensor contains 2 Hall effect switches with 1 shared magnet mounted between them. The magnet and each Hall effect switch are separated by an air gap. A Hall effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the voltage signal is not grounded. If the piece of steel (called an interrupter ring) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON, OFF, ON, OFF, ON, OFF. This ON/OFF signal is similar to the signal that a set of conventional breaker points in a distributor would generate, as the distributor shaft is turned and the points open and close

.FIG : Fig. 1: The Crankshaft Position (CKP) sensor is mounted to the front left side of the timing chain cover


In the case of the electronic ignition system, the piece of steel is 2 concentric interrupter rings mounted to the rear of the crankshaft balancer. Each interrupter ring has blades and windows that, in conjunction with the crankshaft revolution, either block the magnetic field or allow it to reach one of the Hall effect switches. The outer Hall effect switch is called the 18X crankshaft position sensor, because the outer interrupter ring has 18 evenly spaced the same width blades and windows. The 18X crankshaft position sensor produces 18 ON/OFF pulses per crankshaft revolution. The Hall effect switch closest to the crankshaft, the 3X crankshaft position sensor, is called this because the inside interrupter ring has 3 unevenly spaced, different width blades and windows. The 3X crankshaft position sensor produces 3 different length ON/OFF pulses per crankshaft revolution. When a 3X interrupter ring window is between the magnet and the inner switch, the magnetic field will cause the 3X Hall effect switch to ground the 3X signal voltage supplied from the ignition control module. The 18X interrupter ring and Hall effect switch reacts similarly.


See Figures 6, 7 and 8

  1. Disconnect the negative battery cable.
  2. Remove the serpentine drive belt from the crankshaft pulley.
  3. Raise and safely support the vehicle.
  4. Remove the right front wheel and tire assembly and the right inner fender access cover/splash shield.
  5. Using a 28mm socket, remove the crankshaft harmonic balancer retaining bolt.
  6. Remove the crankshaft balancer, using a puller if necessary.
  7. For 1992-99 vehicles, remove the CKP sensor shield.

FIG : Fig. 6: If so equipped, remove the crankshaft position sensor shield


  1. Unplug the sensor electrical connector.
  2. For 1987-91 vehicles, perform the following:
    1. Remove the sensor and pedestal from the block face.
    2. Remove the sensor from the pedestal.

  3. For 1992-99 vehicles, remove the sensor from the block face.

To install:

  1. For 1987-91 vehicles, perform the following:
  2. Loosely install the crankshaft sensor on the pedestal.
  3. Position the sensor, with the pedestal attached, on crankshaft sensor installation tool J 37089 or equivalent.
  4. Install the bolt to hold the pedestal to the block face, then tighten to 14-28 ft. lbs. (20-40 Nm).

    Click image to see an enlarged view

    Fig. Fig. 7: Position the crankshaft sensor tool on the crankshaft

    Click image to see an enlarged view Fig. Fig. 8: Insert the crankshaft sensor tool into the harmonic balancer
  5. Tighten the pedestal pinch bolt to 30-35 inch lbs. (3-4 Nm).
  6. Remove the special tool.
  7. Place the crankshaft sensor tool on the crankshaft balancer and turn. If any vane on the harmonic balancer touches the tool, replace the balancer.

  1. For 1992-99 vehicles, install the CKP sensor on the block.
    1. Install the retaining bolts and tighten to 14-28 ft. lbs. (20-40 Nm).
    2. Install the crankshaft position sensor shield.
    3. Attach the sensor electrical connector.

  2. Install the balancer on the crankshaft.
  3. Tighten the crankshaft bolt to 200-239 ft. lbs. (270-325 Nm) for 1987-91 vehicles. For 1992-99 vehicles, tighten to 110 ft. lbs. (150 Nm), plus an additional 7° rotation.
  4. Install the inner fender shield and the right tire and wheel assembly.
  5. Carefully lower the vehicle.
  6. Install the serpentine belt.
  7. Connect the negative battery cable.