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Thread: knocking sound in Town car

  1. #1
    Senior Member
    Join Date
    Jun 2009
    Edison NJ

    Default knocking sound in Town car

    Hi there,
    Two of my town cars are around 190k mark and they both have slight knocking/cranking sound when the engine is hot/normal temp and when there is load or try to speed up suddenly; it makes a little diesel engine type of noise for brief when under load. I know once upon a time in 2007 a dealer fixed this with his computer and it was gone, the pickup/power was increased and the issue was resolved.

    Another town car has lifter type of noise, specially at cold start if I try to drive within first 5 minute I can hear the lifters noise, later at normal engine operating temp the sound is gone.

    None of the cars have any check engine light on. Spark plugs changed every 45-50k, Oil Fully Synthetic Mobile 1, note: this is a knocking sound, not a hesitating feeling when the ignition coil is bad.
    I was wondering if you had such issues, and how did you manage to solve it in cost effective way.


  2. #2


    Knocking can be caused by gasoline. Try putting a tankful of premium gas in a car and see what happens.

  3. #3
    Senior Member Elegant Limousines of Palm Coast's Avatar
    Join Date
    Apr 2007
    Palm Coast, Fl & Service Daytona, Ormond, Jacksonville, Orlando , St Augustine
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    My experience with Ford's 4.6 engine is it has a slightly higher compression and runs much better and quieter on 91 or 93 octane. A lower grade fuel has a lower flash temperature causing premature igniting of the fuel in higher compression engines. This is where your knock and ping noise comes from. I run all of our Town Cars on Mobil One with lucas oil additive and high octane fuel. Hope this info helps. You may also needto have a carbon cleaning done. Carbon buildup on the pistons and valves can cause higher compression and will result in the same problem.

  4. #4
    Senior Member MrQ45Limo's Avatar
    Join Date
    Feb 2009
    Milwaukee, Wisconsin
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    Have you ever replaced any of your 4 catalytic converters? They get clogged when they get old, and you said you had 190K on this vehicle. Put your hand on the floor where the heal of your driving foot would be, is it really hot? another way is to run it good and hot at night and park it over a pit, or jack it up and see if any of the converters are glowing red hot. knocking could be coming from a clogged exhaust.
    Badger State Limousine Service
    "When nothing less than perfection will do"
    (414)-GO-GO-RED (414)-464-6733

  5. #5
    Join Date
    Aug 2009
    Metro Chicago - Serving Ohare and Midway Airports


    Make sure your serpentine belt tensioner assembly is not rubbing on the timing cover. This will happen under load / accel if there is play in the bearing.
    Hinsdale Limo Service

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