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  Tech Tips

Checklist Helps Pinpoint Source Of Engine that Won't Start

Posted 4/17/2006
By Bill Strehle

“ 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. ”

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.

  • Get the engine as hot as possible to try to duplicate the no-start. Run the engine with the hood closed and the air conditioner on to allow the engine compartment to get as hot as possible. Many heat- related no-starts will not be confirmed if the hood of the vehicle is left open, allowing the heat to escape.
  • Try a "wet test" on the engine and secondary ignition components to see if a little moisture will duplicate the problem.
  • Monitor the 5-volt reference voltage as the no-start occurs. The rule of thumb is that the voltage should not drop below 4.9 volts or higher than 5.1 volts. If the voltage is higher than 5 volts, it indicates a poor ground to the PCM or a short to power. A drop below 5 volts indicates a harness problem or a shorted three-wire sensor.
  • Check the voltage output from the EEC power relay to the PCM not only KOEO, but also during cranking. Voltage may check out OK when the key is on, but may drop drastically when the engine is cranked over.
  • Install the scan tool to see if you can communicate with the PCM. Monitor the rpm PID during cranking for a good signal.
  • Using a spark tester and a noid light, check for spark and injector pulse. If there's injector pulse but no spark, verify battery voltage to the ignition coil. If there's spark but no injector pulse, there may be a PATS issue because the system will shut off the injectors. Verify battery voltage to the injectors. See if the anti-theft light is flashing rapidly. If your scan tool does not have the software needed to access codes from the PATS, leave the key in the "run" position for one minute. After a one-minute time-out, most Ford PATS will output a two-digit flash out code that can be counted observing the anti-theft light.
  • If the engine has spark and injector pulse but still does not start, check cranking vacuum. A good engine should be capable of producing 2 to 5 inches of vacuum during cranking. Exhaust backpressure can be low on a cold exhaust and high on a hot exhaust due to heat expansion. Extreme cold can cause the condensation in the exhaust to freeze and create backpressure problems.

Using these basic principles should pinpoint the source of the problem and leave you with a happy customer.

Guy Dibble Bill Strehle is an Identifix Ford specialist. He is ASE master and L1 certified and has 31 years of diagnostic repair experience.

Experience Identifix This information is provided by IDENTIFIX®. IDENTIFIX® resources cut diagnostic time and provide repair solutions that increase the shop's bottom line. From Repair-Trac pattern failure quick fixes, to Diagram-Online wiring diagrams by fax, to the Repair Hotline staffed by 32 master techs who specialize in diagnosing complex problems by phone or fax, IDENTIFIX® helps techicians fix more cars in less time.

For more information on IDENTIFIX, call (800) 288-6210, 8 a.m. - 6 p.m. Central Time.

www.identifix.com.

© 2011 IDENTIFIX. All Rights Reserved.

© 2006 IDENTIFIX. All Rights Reserved.


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