Technical Car Experts Answers everything you need: engine starts bucking at about high RPM on Ford Ranger 4.0 L engine?

Proper TOOLS LIKE SCREWDRIVER, PLIERS, PRIER, AND PUTTY KNIFE ETC ETC should be kept handy. -----

ALWAYS KEEP MARKER AND HANDY-CAM READY, WHILE PERFORMING THESE JOBS.

MARKER COMES IN USE TO MARK THE POSITION OR PARTICULAR WIRE OR SCREW AND HANDY CAM COMES IN USE FOR GETTING THE EXACT PICTURE OF PART,WHEN IT WAS ASSEMBLED, SO After DIS-ASSEMBLY, YOU CAN JUST VIEW THE PICTURE/PHOTO AND THAT HELPS YOU A LOT while reassembling.

First the basic possibilities needs to be checked.---

This are as follows :---

1) Fuel filters.

2) spark plugs and its wires.

3) Crank shaft position sensor.----------

First of all this basic possibilities needs to be checked.If fuel filter gets clogged, you notice bucking, hesitation jerking type of problem.------

If spark plugs gets very old or spark plugs got loose or dirty, you will notice bucking.

If crank sensor stops getting signal from computer you will notice bucking.------

But if all this possibilities checked out OK, then its a major problem.------

In this major problem, lot of troubleshooting is required, it will be very time consuming.---------

And requires complete technical and mechanical knowledge and tools.----

Bucking at about 3200 RPM or at high RPM.------

You need to check the distributor, When a distributor starts to go bad or act up,exspecially at certain speeds like between 30 to 45 MPH. Also you might want to check the cam sensor. this will act up with the same sympoms as the Distributor.
Here is how to test the camshaft sensor. Look for the one for your engine size and go with the instructions.

Camshaft Position (CMP) Sensor

OPERATION

See Figures 1 and 2

The CMP sensor provides the camshaft position information, called the CMP signal, which is used by the Powertrain Control Module (PCM) for fuel synchronization.

1991-93 2.3L and 1991-95 4.0L (VIN X) engines did not use CMP sensors.

1994 2.3L California only and 1995-99 2.3L and 2.5L engines utilize CMP sensors. The 1994 CMP is located on the oil pump drive assembly, on the left-hand lower side of the engine block. 1995-99 models CMP sensor is located and triggered by the auxiliary shaft drive sprocket.

On the 1991-94 2.9L and 3.0L engine, the distributor stator is the Camshaft Position (CMP) sensor, and it is a hall effect magnetic switch. On the 1995-99 3.0L engine, the CMP is mounted on the oil pump drive assembly, located towards the rear of the block. it is also a single hall effect magnetic switch and it is activated by a single vane, and is driven by the camshaft.

Fig. Fig. 1: Camshaft Position (CMP) sensor used on the 2.3L and 2.5L engine-except 1994 California

Fig. Fig. 2: Oil pump drive mounted CMP sensor used on 3.0L, 4.0L and 5.0L engines and 1994 California 2.3L engines

On the 4.0L SOHC engine (VIN E), the Camshaft Position (CMP) sensor is a variable reluctance sensor , which is triggered by the high-point mark on the left-hand camshaft. It is mounted to the valve cover.

The 4.0L and 5.0L engines use a separate CMP sensor mounted to the oil pump drive. The drive assembly is located toward the rear of the engine on the 4.0L, and towards the front on the 5.0L engine.

TESTING

Three Wire Sensors

See Figure 3

With the ignition OFF , disconnect the CMP sensor. With the ignition ON and the engine OFF , measure the voltage between sensor harness connector VPWR and PWR GND terminals (refer to the accompanying illustration). If the reading is greater than 10.5 volts, the power circuit to the sensor is okay.

With the ignition OFF , install break-out box between the CMP sensor and the PCM. Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure voltage between break-out box terminals 24 and 40 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt, the sensor is okay.

Fig. Fig. 3: CMP sensor wire harness connections for the 3-wire sensor

Two Wire Sensors

See Figure 4

With the ignition OFF , install a break-out box between the CMP sensor and PCM.

Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure the voltage between break-out box terminals 24 and 46 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt AC, the sensor is okay.

Fig. Fig. 4: CMP sensor wire harness connections for the 2-wire sensor

REMOVAL & INSTALLATION

1995-97 2.3L and 1998-99 2.5L Engines

According to the manufacturer, the A/C system, if equipped, must be discharged for this procedure. Have your A/C system refrigerant reclaimed by an MVAC certified repair shop. However, there may be enough flex or slack in the A/C lines to allow you to support the compressor off to the side without disconnecting the lines.

Disconnect the negative battery cable.

Remove the accessory drive belt.

Remove the four bolts securing the A/C compressor to the mounting bracket and set aside.

Remove the three compressor/power steering bracket retaining bolts.

Pull the bracket, with the power steering pump attached, away from the engine and position it aside.

Disconnect the engine control sensor wiring from the camshaft position sensor.

Remove the two CMP mounting bolts and then pull the sensor from the oil pump.

To install:

Install the CMP sensor to the oil pump and tighten the two mounting screws to 45-61 inch lbs. (5-7 Nm).

Reconnect the engine control sensor wiring to the sensor.

Position the bracket, with the power steering pump attached, to the engine.

Install the three compressor/power steering bracket retaining bolts and tighten securely.

Install the A/C compressor to the mounting bracket and tighten the four mounting bolts.

Install the accessory drive belt.

Connect the negative battery cable. Start the engine and check for leaks.

1991-94 2.9L and 3.0L Engines

Refer to Engine Electrical in this information for distributor removal and installation.

1995-99 3.0L, 4.0L (VIN X), 5.0L and 1994 California only 2.3L Engines

See Figures 5, 6, 7 and 8

If the camshaft position sensor housing does not contain a plastic locator cover tool, a special service tool such as T89P-12200-A, or equivalent, must be obtained prior to installation. Failure to follow this procedure may result in improper stator alignment. This will result in the fuel system being out of time with the engine, possibly causing engine damage.

Disconnect the negative battery cable.

Remove the ignition coil , radio capacitor and ignition coil bracket.

Disengage the wiring harness connector from the CMP sensor.

Prior to removing the camshaft position sensor, set the No. 1 cylinder to 10° After Top Dead Center (ATDC) of the compression stroke. Note the position of the sensor electrical connection. When installing the sensor, the connection must be in the exact same position.

Position the No. 1 cylinder at 10° ATDC, then matchmark the CMP sensor terminal connector position with the engine assembly.

Remove the camshaft position sensor retaining screws and sensor.

Remove the retaining bolt and hold-down clamp.

The oil pump intermediate shaft should be removed with the camshaft sensor housing.

Remove the CMP sensor housing from the front engine cover.

Fig. Fig. 5: Exploded view of the Camshaft Position (CMP) sensor mounting for the 3.0L engine-4.0L and 5.0L engines are similar

To install:

If the plastic locator cover is not attached to the replacement camshaft position sensor, attach a synchro positioning tool, such as Ford Tool T89P-12200-A or equivalent. To do so, perform the following:
1. Engage the sensor housing vane into the radial slot of the tool.
2. Rotate the tool on the camshaft sensor housing until the tool boss engages the notch in the sensor housing.The cover tool should be square and in contact with the entire top surface of the camshaft position sensor housing.
  
  Fig. Fig. 6: Attach the CMP synchro positioning tool to the housing
  
  Fig. Fig. 7: CMP sensor positioning for the 3.0L (75) and 4.0L (60) engines
  
  Fig. Fig. 8: CMP sensor positioning for the 5.0L engine

Transfer the oil pump intermediate shaft from the old camshaft position sensor housing to the replacement sensor housing.

Install the camshaft sensor housing so that the drive gear engagement occurs when the arrow on the locator tool is pointed approximately 7° counterclockwise (the sensor terminal connector should be aligned with its matchmarks) from the face of the cylinder block.

Install the hold-down clamp and bolt, then tighten the bolt to 15-22 ft. lbs. (20-7 Nm).

Remove the synchro positioning tool.

CAUTION

If the sensor connector is positioned correctly, DO NOT reposition the connector by rotating the sensor housing. This will result in the fuel system being out of time with the engine. This could possibly cause engine damage. Remove the sensor housing and repeat the installation procedure beginning with step one.

Install the sensor and retaining screws, tighten the screws to 22-8 inch lbs. (2-4 Nm).

Attach the engine control sensor wiring connector to the sensor.

Install the ignition coil bracket, radio ignition capacitor and ignition coil.

Connect the negative battery cable.

4.0L SOHC Engine (VIN E)

Disconnect the negative battery cable.

Disconnect the engine control sensor wiring from the camshaft position sensor.

Remove the sensor retaining screw and the sensor from the left-hand valve cover.

To install:

Make sure the camshaft position sensor mounting surface is clean and the O-ring is positioned correctly.

Position the sensor, then install the retaining screw and tighten it to 71-106 inch lbs. (8-12 Nm).

WARNING

Do not overtighten the screw; you may damage the sensor if the retaining screw is overtightened

Engage the wiring harness connector to the CMP sensor.

Connect the negative battery cable.

--------------

ALSO THE problem can be with the sychronizer.

Test the sensor:

Three Wire Sensors

See Figure 3

With the ignition OFF , disconnect the CMP sensor. With the ignition ON and the engine OFF , measure the voltage between sensor harness connector VPWR and PWR GND terminals (refer to the accompanying illustration). If the reading is greater than 10.5 volts, the power circuit to the sensor is okay.

With the ignition OFF , install break-out box between the CMP sensor and the PCM. Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure voltage between break-out box terminals 24 and 40 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt, the sensor is okay.

Fig. Fig. 3: CMP sensor wire harness connections for the 3-wire sensor

Two Wire Sensors

See Figure 4

With the ignition OFF , install a break-out box between the CMP sensor and PCM.

Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure the voltage between break-out box terminals 24 and 46 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt AC, the sensor is okay.