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  1. #1
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    Default Intake back firing

    84 led lx 5.0 SEFI t5.
    The car ran great before. After a year of rebuilding the rear end and transmission it has developed an intake backfire. It seems to bog down when you launch it from a dead stop, and when you are driving along in 2 or 3 gear and go full throttle you get intake back firing. According to what I have found on the internet it could be timing, bad O2 sensors, vacuum leaks or stuck exhaust valves. I Rechecked the timing, looked for vacuum leaks. I will run the codes to see if o2 sensors show up.
    What is involved in checking the exhaust valves.

  2. #2
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    Blown leaky POWER VALVE in your carb has been the problem some of the time and is a relatively easy cheap fix clean passages and replace

  3. #3
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    It is a fuel injected engine

  4. #4

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    Throttle position sensor comes to mind.

  5. #5

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    Or codes, aren't the 84 motors eec-iv?
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  6. #6

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    lean condition or timing events wrong
    check for vacuum leaks and timing
    1986 GT T Top- stock except for magnaflow cat back
    1990 LX vert- 500hp V3 and all that stuff
    2013 GT- usual bolt ons

  7. #7
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    That is what I figured. I have checked for vacuum leaks, there may be one that I have not found. I need to go back and recheck everything on the timing.

  8. #8

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    Quote Originally Posted by bgriff View Post
    That is what I figured. I have checked for vacuum leaks, there may be one that I have not found. I need to go back and recheck everything on the timing.
    Is it a pop or an actual backfire? If it is popping, it sounds lean, like it's not getting enough fuel. If it's an actual backfire, you may have a deeper problem. Checking the vacuum with a gauge is a great way of checking general engine health. You can find charts online of what normal vacuum should be, and what you see when there is a problem.

  9. #9
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    Quote Originally Posted by blueox76 View Post
    Is it a pop or an actual backfire? If it is popping, it sounds lean, like it's not getting enough fuel. If it's an actual backfire, you may have a deeper problem. Checking the vacuum with a gauge is a great way of checking general engine health. You can find charts online of what normal vacuum should be, and what you see when there is a problem.
    I have been sidetracked by a major water leak in my house, so I haven't spent anytime on the ltd. I did notice that my adjustable aeromotive fuel pressure regulator is not adjusting. It seems stuck on 35 lbs.

  10. #10

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    Make sure the ignition timing was set with the SPOUT connector removed. And I would also verify that
    the outer ring on the crank damper still shows true TDC.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ... '68 Vert, Mexican block 307 4-speed...
    '71 Datsun 510 ... And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  11. #11
    FEP Power Member Ourobos's Avatar
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    Sounds like a vacuum leak to me.
    1986 CHP SSP Coupe

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