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Only 6V on my Explorer fuel pump? Won't start. PATS?

Discussion in 'Under the Hood' started by vk2gom, June 17, 2014.

^^Searches ExplorerForum.com^^





  1. vk2gom

    vk2gom New Member

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    My '97 Explorer XLT stopped suddenly the other day, and I needed towing home.

    I assumed the fuel pump had died, so bought another.

    However, after a bit of poking around, there is only 6V at the pump, as well as at the inertia cut-off switch. All fuses are intact, All relays are good.

    Having a read on the forum here, it appears it's a PATS 'feature' of cutting the power down to the fuel pump to stop it operating.

    But why? I have a genuine transponder key, and it's been fine and reliable since I bought the car. It just stopped with no warning, and hasn't started since.

    The key/security symbol on the dash only illuminates momentarily when turning the ignition on (as it would normally), then it goes off, but crank and crank the starter and it just won't fire. It's not like the key/security symbol is flashing...

    There is zero fuel pressure at the Schraeder valve test port. The fuel pump (and probably injectors) are basically disabled.

    Any thoughts?

    Thanks - Rob
    Sydney, Australia.
     
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  3. TestPoint

    TestPoint Active Member

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    Perhaps the Australian '97 had PATS but the US version did not until '98.

    Before spending any more time thinking about PATS resolve your fuel pump electrical issue. If you are reading 6v it sounds like corrosion or a failed pump. My '00 PATS enabled Explorer only disabled the operating signal to the injectors.
     
  4. vk2gom

    vk2gom New Member

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    OK, I have done a bit more diagnosis and digging.

    The fuel pump IS getting 12V for about 3 secs when I turn the ignition on, which reading around the web, seems correct. I was only seeing 6V since I was turning the ignition on, then going to measure, by which time the Voltage had dropped to 6V. I rigged my Voltmeter off the inertia switch so I could sit in the drivers seat, turn the ignition on, and see the 12V appear for 3 secs.

    But still no fuel at the Schraeder valve. So frustrating :(

    I just replaced the fuel filter with a new one. Some dirty fuel came out of the tank end, and clean fuel from the engine end of the old one. I blew down it to test. Not as free flowing as the new one, but it was flowing.

    Is there any sort of fuel shut-off valve on the '97 4.0 V6 engine? I have taken the plastic cowling top off the engine, and can see the braided fuel lines to each fuel rail. I can only trace them back so far before they disappear under the bottom of the engine.

    Any advice welcome.

    Thanks - Rob
     
  5. TestPoint

    TestPoint Active Member

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    Two suggestions:

    New pump is bad

    You wired the pump backwards . . . sucks that way.
     
  6. vk2gom

    vk2gom New Member

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    Anything is possible... I'll check +ve is going to the +ve marked on the pump body. I didn't think it was possible to get it wrong given the connectors are keyed, but you never know!

    Also, from dry, how much cranking would it need to fill the filter and hoses and to the fuel rail? I'm guessing I gave it 20 secs or so and no signs of firing at all.

    Thanks - Rob
     
  7. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    PCM monitors fuel pump relay

    The PCM controls the fuel pump relay and monitors its output. The +6 volts you're reading is from the PCM input that monitors the fuel pump relay output.

    If there is battery voltage at the inertia switch when the starter is cranking the engine then everything prior to that is functional. The PCM knows when the engine is rotating via the crankshaft position sensor and opens the relay if the crankshaft position sensor is not pulsing.

    Turn the ignition key on/off/on three times while monitoring fuel pressure. It should increase each time the pump runs for a few seconds. By the third time the pressure should be normal. If it isn't and there is battery voltage at the inertia switch output then either the fuel pump is bad, or the wiring to/from it is bad, or the fuel supply is blocked. You can remove the fuel pump relay and apply a battery charger output to the power contacts and the pump should run continuously.
     
  8. vk2gom

    vk2gom New Member

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    Thanks for the info. Checking for battery Volts whilst cranking gives me something to look for tomorrow.

    I have also cleaned up the crank angle sensor connector a few days ago with switch cleaner spray.

    In the meantime, my pushbike is getting more km on it than ever before!

    Thanks - Rob
     

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