Question about 1999 Ford Ranger SuperCab

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99 Ford Ranger XLT 3.0L V6 Intermittent ignition

OK - For the last 10 years the Ranger has started perfectly every time. Last week, for the first time, I turn the engine over and it would not run. It sounded like none of the cylinders were firing so I pulled a spark plug, grounded it and turned the engine over, no spark. After half an hour of fiddling with connectors and swearing under my breath the engine started and ran like it was new. This all happened (BTW) when I was 40 miles from home so after the engine started I drove it home without any trouble. The next morning, same thing, the engine would turn over but not run. No spark. Between then and now, I've checked the coil pack by ohming out between the Batt+ terminal and each of the three coil primaries (same connector) and I get 2.5 to 3 ohms. No opens or dead shorts. Next, I checked the crankshaft sensor for output by looking at the two terminals with an o-scope. While cranking the engine over I'll see a steady sine wave output - proportional to the crankshaft RPM. Outputs everytime so I rule that one out. BTW, when the engine is in this failure mode the PCM does not generate any error codes or check engine light - nothing.... So I'm thinging that may it's a wiring harness connector problem or perhaps a flaky ground connection. Any suggestions as to the root of this intermittent problem would be greatly appreciated.

Thanks.

Chris.

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  • 2 more comments 
  • cdewaal Feb 21, 2009

    Hi 69 fastback, No I haven't looked at the injectors yet, nor have I done anything with the PCM connector. I've been focusing on the ignition system since I was able to confirm that the coil pack was not firing. I'll do some more work on the truck this morning. If it doesn't run, I'll check to see if the injectors are getting a pulse from the PCM. If there's no pulse, I'll work back to the PCM and check the condition of the connector. Another friend suggested to inspect the ignition switch as well. It's a high use item and might have a contact going bad.

  • cdewaal Mar 01, 2009

    Update... The engine has been starting fine for a week now. Today, it turns over but wont run. So, I popped the coil pack connector and checked to see if there was +12V on the red wire. It's there. Next, I checked the other three wires that run back to the PCM. While turning over the engine, the PCM should pull these lines low to fire the coil but this time it's not happening. Each of the three lines are inactive. So, the PCM is not firing the coil pack. The question is why?

  • cdewaal Mar 01, 2009

    Additional comment. I've pulled the bulkhead connector to the PCM and checked the condition of the contact pins. No sign of water ingress or corrosion. To be safe, I cleaned the pins with the appropriate electrical contact cleaner (leaves no film). Still that does not solve the problem. I wonder if there's another sensor input to the PCM that's causing trouble. Anyone??


  • 69 fastback May 11, 2010

    Is there a pulsing signal at the injectors during the no start? Have you disconnected the PCM and looked for water intrusion at he connector?

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I would have to suspect a crank sensor and-or connection there.
i see you checked it with an "o-scope" but i would be willing to
bet you dont have injector pulse either. without the crank signal, there is no rpm input, the pcm doesnt even know its cranking!
i have replaced many crank sensors with this intermitent concern....

Posted on Jun 02, 2010

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