Question about 1990 Ford F150

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Fuel pump just replaced has 58 pd pressurewhen turing overand 55 pd sitting still not runnig . still won't crank what else could it be replaced fuel filter it has a 4.9 motor in it what else could be wrong

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  • Ford Master
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The fuel pressure is probably not an issue. Does it have spark? How about the ignition timing? If a crank sensor is bad, then the car won't start.

Crankshaft Position (CP) Sensor OPERATION The CP sensor is mounted on the right front of some V8 engines, is a variable reluctance sensor triggered by a trigger pulse wheel (36 minus 1 tooth). Its purpose is to provide the PCM with an accurate ignition timing reference (when the piston reaches 10 degrees BTDC) and injector operation information (twice each crankshaft revolution). The crankshaft vibration damper is fitted with a 4 lobe pulse ring. As the crankshaft rotates, the pulse ring lobes interrupt the magnetic field at the tip of the CP sensor.

TESTING Using DVOM on the AC scale and set to monitor less than 5V, measure voltage between the sensor Cylinder Identification (CID) terminal and ground. The sensor is okay if the voltage reading varies more than 0.1V AC with the engine running at varying RPM. --- Check for spark but there are a few different ignition system problems to be considered, on this Ford F-150 from 1990. Dura Spark II vs. TFI-IV System, Ignition Module problem Ignition Coil Problem. --- The following outlines testing the Ignition Coil problem: TESTING Ignition Coil Test The ignition coil must be diagnosed separately from the rest of the ignition system.

  1. Primary resistance is measured between the two primary (low voltage) coil terminals, with the coil connector disconnected and the ignition switch off. Primary resistance should be 0.3-1.0 ohms.
  2. On Dura Spark ignitions, the secondary resistance is measured between the BATT and high voltage (secondary) terminals of the ignition coil with the ignition OFF, and the wiring from the coil disconnected. Secondary resistance must be 8,000-11,500 ohms.
  3. If resistance tests are okay, but the coil is still suspected, test the coil on a coil tester by following the test equipment manufacturer's instructions for a standard coil. If the reading differs from the original test, check for a defective wiring harness.
Ignition Coil Primary Circuit Switching
  1. Insert a small straight pin in the wire which runs from the coil negative (-) terminal to the TFI module, about 1 in. (25mm) from the module. WARNING
    The pin must not touch ground!
  2. Connect a 12 VDC test lamp between the straight pin and an engine ground.
  3. Crank the engine, noting the operation of the test lamp. If the test lamp flashes, proceed to the next test. If the test lamp lights but does not flash, proceed to the Wiring Harness test. If the test lamp does not light at all, proceed to the Primary Circuit Continuity test.
Ignition Coil Resistance Refer to the General Testing for an explanation of the resistance tests. Replace the ignition coil if the resistance is out of the specification range. Ignition Coil Secondary Voltage
  1. Disconnect the secondary (high voltage) coil wire from the distributor cap and install a spark tester between the coil wire and ground.
  2. Crank the engine. A good, strong spark should be noted at the spark tester. If spark is noted, but the engine will not start, check the spark plugs, spark plug wiring, and fuel system. If there is no spark at the tester: Check the ignition coil secondary wire resistance; it should be no more than 5,000 ohms per foot. Inspect the ignition coil for damage and/or carbon tracking. With the distributor cap removed, verify that the distributor shaft turns with the engine; if it does not, repair the engine as required. If the fault was not found proceed to the Ignition Coil Primary Voltage test.
Ignition Coil Primary Voltage
  1. Attach the negative lead of a voltmeter to the distributor base.
  2. Turn the ignition switch ON and connect the positive voltmeter lead to the negative (-) ignition coil terminal. Note the voltage reading and turn the ignition OFF. If the voltmeter reading is less than 90 percent of the available battery voltage, inspect the wiring between the ignition module and the negative (-) coil terminal, then proceed to the Ignition Coil Supply Voltage test.
Ignition Coil Supply Voltage
  1. Attach the negative lead of a voltmeter to the distributor base.
  2. Turn the ignition switch ON and connect the positive voltmeter lead to the positive (+) ignition coil terminal. Note the voltage reading then turn the ignition OFF. If the voltage reading is at least 90 percent of the battery voltage, yet the engine will still not run; first, check the ignition coil connector and terminals for corrosion, dirt, and/or damage; second, replace the ignition switch if the connectors and terminal are okay.
  3. Connect any remaining wiring.
fuel pump just replaced has - prev.gif next.gif --- Further testing may be done, but I would recommend getting a Chilton, Haynes, or manufactuer's service manual for this.

Posted on Oct 12, 2010

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