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Engine Missing Under Load

Discussion in '80-Series Tech' started by Scamper, Nov 29, 2003.

  1. Scamper

    Scamper

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    I've noticed over the past month or so that when under load (towing a trailer uphill), I feel an occaisional "bump" from the engine and/or drivetrain when I shouldn't feel that--feels to me like a missing engine though the engine on this truck is so insulated I have a hard time discerning this. As far as I can tell, it's not from the road/suspension since it also occurs on smooth roadway. It occurs more when under heavy load than under light load. Under normal driving conditions, I amost never feel this.

    I've recently replaced plugs, wires, dist, and rotor, and have done a fuel injector and TB cleaning using 3M stuff (in order to try to make this go away). Rotor and Dist were not OEM. I checked the timing and it's dead on (yes, with the jumpers jumped on the diag port). I've also done a search here and can't find anything related to "missing"...

    Anyone know what this could be and what the fix is? My next step would be to replace the dist. and rotor with OEM, but since all are only a few months old, I really don't think this is it. TIA.

    Tom
     
  2. Beowulf

    Beowulf

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    Tom,
    >> Rotor and Dist were not OEM. <<

    They're cheap and easy to replace. If replacing doesn't fix the miss then you have some trail spares.

    Did you use OEM plug wires? Several guys have reported performance problems with aftermarket wires.

    Another possibility is the engine wiring harness. A few guys have reported these will chafe and short an injector wire (intermittent short to ground.) One guy found his problem in the cabin under the PS dash. Others have found the problem in the wiring harness next to the EGR valve. When you inspect the harness next to the EGR valve be very careful as this location is prone to overheating the harness. A good fix is to use heat shielding material from a race shop.

    -B-
     
  3. sjcruiser

    sjcruiser

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    Tom,

    It sounds more like a fuel supply issue (starvation). Have you changed the filter (see you having a SC) yet ?

    Frank.
     
  4. yooper

    yooper Lost user SILVER Star

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    If it was a 3FE, I'd say Fuel Pressure Regulator, the root of all 3FE fuel system problem evil.
     
  5. Scamper

    Scamper

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    -B-: got the wires from Dan (the OEM wires are really nice!). But I had forgotten to order the cap and rotor from him at the time and so I just went to the local car place. You know how it is when you don't use quality parts...it just keeps nagging at your mind and now that I'm noticing something wrong, it keeps on coming back to me. So yes, I'll be replacing those shortly.

    Now that you mention it, I do remember seeing the thread(s) on that wiring harness. I'll go back and look them up and check it for problems. Thanks.

    Frank: my initial thoughts were that I was leaning out due to bad or dirty injectors which is why I did the T/B and injector cleaning (I think I'm also seeing slightly higher than "normal" EGTs). But other than running a tad smoother after cleaning, it has not stopped this missing thing. The filter was replaced less than a year ago, after the S/C was put on, so I'm pretty confident that it's okay.

    Yooper: probably worth checking all fuel components for any obvious problems, even though it's not a 3FE.

    Thanks guys,

    Tom