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2000 F150 Bifuel starts/runs on CNG only when cold

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  • 2000 F150 Bifuel starts/runs on CNG only when cold

    Help! My daughter has a F150 that was diagnosed as needing a new regulator... Symptoms were that it would start on CNG (easily) when cold, and would run fine until you turn off the engine (for an instant or for an hour) then it would crank and fail over to run on regular gas.

    Now I'm glad that CNGparts gave me the opportunity to put in an affordable regulator (I refused to pay the ~$1K many months ago that I was told it would cost from Ford, even if one could be found).

    With the new (used P71-100) regulator, the truck started up first crank and I drove it for a short while, stopped, and it restarted fine... I thought I was good to go until my daughter drove for a bit longer, stopped at a store, and had the same problem trying to restart the warm engine.

    Has anyone ever seen this type of behavior and have any ideas for further troubleshooting? Thanks!
    2008 GX (extended range, trunkless version)
    Polished Metal Metallic 2012 Civic Natural Gas
    Fuelmaker FMQ-2-36 (since 2001)
    Previously owned: 2000 GX (11 years), 1995 Bi-fuel Sonoma, 2000 Bifuel Tahoe, 2000 Bi-fuel F150