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Thread: 4.8 lost power+knock

  1. #1
    Join Date
    Jan 2014
    Posts
    154

    4.8 lost power+knock

    Drove my truck yesterday after i got my power steering hooked up, all was well with no problems. The ol'lady drove it to school today, she stopped at mcy'ds for a bite of breakfast, whent to hope back on i40(Arkansas) and it had no power at all. She called me and said she was smelling gas. I though well mabey a spark plug when completely out. No big deal. Looked and had a small leak on the return line. Tightened it up no more leak. Had her grab a set of plugs to change them after work along with a new set of plug wires. Well auto zone can't get the wire I want till Monday so I didn't bother with changing the plugs.
    Whent to the beer store to grab some cold ones for a good warm Friday night, and she was right. It has absolutely no power, and a knocking sound at the right load on the motor and right rpm.
    All this happened sitting at McDonald's waiting on food. No clack, bang or spuder that she noticed wile sitting there.
    So, is it a sensor or mechanical?
    Motor is still under warranty so I need to figure it out before its gone.

  2. #2
    Join Date
    Jan 2014
    Posts
    154
    Got the codes read, 1st is p0102=maf or map sensor
    The other is p0200 which has to do with the fuel system.
    With a short/open circuit on one or more injectors, bad regulator, or return line blocked.
    Would any of this cause a knock under engine load (like climbing a hill)

  3. #3
    Join Date
    Apr 2006
    Location
    Bellevue, Nebraska
    Posts
    1,304
    What year truck?

  4. #4
    Join Date
    Jan 2014
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    154
    95 with 2001 4.8

  5. #5
    Join Date
    Mar 2003
    Location
    San Antonio, TX
    Posts
    11,038
    P0200
    An injector wire issue, possibly.

    102. Maf related. May be a wire or terminal. Pretty common.

  6. #6
    Join Date
    Jan 2014
    Posts
    154
    Got the mass air flow changed out, runs like a champ and the knock went away. But, a ticking sound came back. Over the whole rpm range (idle-wot) hot or cold. Doesn't matter.
    The exhaust isn't hooked up, so there isn't any back pressure so I'm ruling out exhaust leak for the moment, next I'm going to check the rockers. Just changed the plugs, plug wires will be in tomorrow as well as exhaust hooked up. What els can cause a constant tick besides a bad lifter?

  7. #7
    Join Date
    Jan 2014
    Posts
    154
    Well, problem came back. Going to get a new sensor tomorrow. But, I'm not sure if that's my problem or not. Its "went out" about the same time of driving. Probley 10 miles after each sensor it losses power.

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