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won't start

  #1  
Old 12-31-2018, 09:28 AM
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My 95 Explorer is at it again. Sometimes it wont start, sometimes it does. Only when you put the key in and hear the fuel pump turn on will it start. When you do not hear the pump it wont. Can the ignition switch have anything to do with it? Ford put a new one in and when either in the on or accessory position, you can remove the key. That seems odd. I replaced the fuel sensor switch in the smart box and pulled it out and checked for a short, which I think a ground short is the problem but not sure. Can it be the cam position sensor? At a loss here. All feedback greatly appreciated.
Thanks,
 
  #2  
Old 12-31-2018, 10:37 AM
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OE fuel pump?

If there’s no pump run cycling the key, Checking at the fuel pump relay connector in the power distribution box for ‘hot at all times’ power distribution, ‘switched’ imput from the ignition, and a needed ‘ground’ for the relay (pcm controls the relay applying a ground) for relay activation,. Do you have a volt/ohm meter?

As a pump test ONLY, you can also remove the relay and bridge the relay connector with a test wire basically bypassing/removing PCM control and a ignition switched input. With a bridge wire in place, the pump would/should run continuous . If the pump runs, either the PCM isn’t supplying a ground, possible a power distribution dropout from the ingition or hot at all times is missing, or the relay itself.
If the OE pump, good chance a pump issue..


 

Last edited by Hayapower; 12-31-2018 at 11:08 AM.
  #3  
Old 12-31-2018, 11:45 AM
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Pump was replaced a few years back. Thought pumps just failed, not going bad? Could it be a short. You don't hear the buzz on the dash when it wont start. When it will start, you can clearly hear a buzz on teh left side of dash by a/c vent.
 
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Old 12-31-2018, 11:53 AM
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Truck has about 200K miles but is in excellent condition. I'm a fanatic


 
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Old 12-31-2018, 11:54 AM
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Pics attached
 
  #6  
Old 12-31-2018, 01:31 PM
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Clean rig..

Not sure what you mean by a buzz?
Generally you'll hear a few relays click with the Key cycled, and the pump will make a whine/hiss sound for a few seconds (if not started) as it pressurizes the system.
Pumps can fail intermittent, do all the time. Sometimes if its a pump start up issue within the pump motor itself, if someone cycles the key On and your giving the bottom of the tank a hefty bump with the flat of your hand (at the same time they cycle the key) at times they'll come to life.
If power distribution is suspect, you can also check for 12v/batt voltage at the inertia switch during a no start. Present, or missing voltage?


But as noted above (and if inertia power is missing),, an easy way to test run the pump during a no start event and/or part of a diagnosis, is to check for power distributions (2) and the much needed key cycled/timed PCM ground (1) at the fuel pump relays connector. Sometimes you have to prove out 'whats there' as far as needed inputs, before you can guess at whats not. missing, or broke/failing..

If the connector is test wire bridged, the engine will start without the PCM applying a ground, or, if the ignition switch input happened to be missing.
 
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Old 01-02-2019, 01:46 PM
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Thank you for the tips. The fuel pump was replaced about 15 years ago. It starts and runs fine. Then it won't start. No sound of the pump cycling when key is turned on. Won't start for days, weeks sometimes. Then it starts fine? Probably just replace the pump and then see if it was the pump and or a ground short.
Thanks Again.
 
  #8  
Old 01-02-2019, 09:51 PM
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During a no start condition,, it’s easy enough to check the pump run at the relays connector face.
If the relay connector is bridged, and the pump springs to life,, good chance it’s not the pump. If it doesn’t run, most likely the pump itself..
15 years is significant, and could certainly be the pump, but I’d try and troubleshoot the pump before a replacement.

If a no start,, do like I mentioned, have someone cycle the key to ON at the very time you give the bottom of the fuel tank a hearty bang.. If the pump starts,,, there’s your answer.. Doesn’t always work, but more often than not..
 
  #9  
Old 01-03-2019, 07:13 AM
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Going to try that and let you know.
Thank you for the reply's.
 
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