2006 Liberty cranks will not start when warm but OK when cold

Discussion in 'KJ General Discussion' started by RodMac, Jan 12, 2020.

  1. RodMac

    RodMac New Member

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    2006 Liberty cranks, starts, and runs perfectly when engine is cold.

    If you drive 10 miles and turn it off and wait 5 min it will crank and not start. Wait 10 more min. and it will start.

    I replaced just the fuel pump, not the entire assembly and it does the same thing.

    Engine Running fuel pressure is 50 psi
    Engine off, after running waiting 10 min., fuel pressure is 52 psi and gets a crank no start.

    I can get it to start 3 different ways when I get a crank no start with a warm engine:

    1) If I drain the fuel pressure from the fuel rail shredder valve the Liberty will start perfectly and run well.
    2) If I let it sit for 15 min. or more it will start.

    3) If I spray brake cleaner down the intake it will start.

    Anyone have any ideas or next steps with troubleshooting?
     
    Last edited: Jan 12, 2020
  2. Billwill

    Billwill Full Access Member

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    Usually the cam or crank sensor fails when hot. Sometimes will post a CEL for the failing part so you need to read out the CEL codes stored....most common failure is the Crank Sensor.

    Download the 2006 KJ-SM.pdf here....the bottom of the Index Page lists the CEL codes and tells you which page to go to for that code.

    Section 8W has the wiring diagrams.

    www.colorado4wheel.com/manuals/Jeep/KJ/
     
    Last edited: Jan 13, 2020
  3. RodMac

    RodMac New Member

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    Thanks Billwill. I’ll check it out.
     
  4. RodMac

    RodMac New Member

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    Well no luck. No CEL. I changed the cam and the crank sensors with Mopar replacement parts. It is doing the exact same thing.

    Any ideas???
     
  5. Billwill

    Billwill Full Access Member

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    What CEL codes do you have?
    Could be some other Sensor.

    Is this a Gasser or a CRD?
     
  6. RodMac

    RodMac New Member

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    There are no CEL’s. Just will crank/no start when it sits for 15 minutes after driving. It is a gas engine.

    I swapped the ASD relay this morning. And then verified signals to PCM. I pulled relay and then put test lights between 30 and 87. Also a test light between 85 and 86. Both lights came on while cranking during no start. Also OHMed relay. All was good but still a crank/no start.

    I verified spark and fuel injector voltage cycling during crank/no start also.

    One shot of brake cleaner in the brake booster vacuum line that connects to intake manifold and it starts up and runs well

    I am out of ideas
     
  7. Billwill

    Billwill Full Access Member

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    Sounds like a fuel supply issue.....these often do not set a CEL.

    When you drain the fuel from the fuel rail shredder valve it seems to work.

    Fuel pump/filter OK and not getting air into the fuel lines?:confused:

    I am not an expert on gasser fuel supply problems so I will leave that to the real Experts here...I specialize in electrical problems!;)
     
  8. Azmodeus

    Azmodeus New Member

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    Over there, over there, over there and up there..
    have you checked/cleaned or swapped your injectors?
     
  9. RodMac

    RodMac New Member

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    Took the Jeep to the local dealer this week. They could not figure it out for sure, but said when driving the fuel pressure drops to 35 psi. They think this low pressure when driving may allow fuel vaporization when Jeep is then parked after driving. They suggested changing the fuel pump assembly because it contains the pressure regulator and I only changed the actual pump.

    New Denso fuel pump assembly comes Tuesday. I’ll post if it fixes the issue.
     
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  10. RodMac

    RodMac New Member

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    Replaced fuel pump assembly. After two days I have had no issues with the crank/no start. I believe the issue is fixed. Must have been the fuel regulator in the fuel pump assembly. Big thanks to Southern Jeep in Chesapeake VA for putting me in the right direction.
     
  11. RenKJ

    RenKJ Full Access Member

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    I think i have this issue just starting today, no codes, intermittent issue when starting the engine hot, it hiccups and seems to want to start but fails, can you link a part number of what you ended up swapping?