Checklist Helps Pinpoint Source Of Engine that Won't StartPosted 4/17/2006
By Bill Strehle
Does this scenario sound familiar? The vehicle does not start. When it comes into the repair facility, the engine starts right up and runs fine. Most often there are no codes in the computer memory. The tech replaces parts on the vehicle from an educated guess but that doesn't solve the intermittent no-start. End result: a frustrated technician and an unhappy customer.
Here are a few simple things to check - no special tools required - to help you and your customer verify the no-start.
Is the "Check Engine" light (CEL) on when the key is in the run position? Fords are designed to illuminate the CEL when the key is in the key on, engine off (KOEO) position. If the light does not come on, it may indicate a defective electronic engine control (EEC) power relay, a blown fuse, a defective powertrain control module (PCM), harness problems or a shorted three-wire sensor.
Does the fuel pump run for a short duration, KOEO, to prime up the fuel rail? If the CEL is on, this indicates the PCM is powered up. The PCM will ground the fuel pump relay for 3 to 5 seconds to allow the fuel rail to get primed up and will turn the fuel pump off if it does not see a cranking rpm. You can usually hear the fuel pump run if the radio and the A/C blower motor are turned off.
Does the CEL go out when the engine is cranked over? If the PCM receives a signal from the crankshaft sensor or the ignition module, the CEL should go off when cranking. If the light stays on steady, the PCM is not receiving a crankshaft sensor signal and will not provide injector pulse or spark.
Is the anti-theft light blinking rapidly KOEO or during cranking? This indicates a problem with the passive anti-theft system (PATS) or that this system is not communicating with the PCM.
Is the engine hot or cold during the no-start? Many problems are heat related. The engine will start when it cools off.
What about the weather? Some problems are moisture related. When the engine dries out, it will start and run fine.
Using these guidelines as a checklist, the source of the no-start can often be narrowed to a particular system. If the no-start checklist proves to be inconclusive, the next approach is to install three basic tools on the vehicle: a fuel pressure gauge, a voltmeter and a scan tool. Get the customer's permission to drive the vehicle on parts runs or during your lunch break so you can try to duplicate the symptoms.
Using these basic principles should pinpoint the source of the problem and leave you with a happy customer.
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