please HELP

Discussion in '4.0 Engine' started by nicarc369, Aug 5, 2010.

  1. nicarc369

    nicarc369 New Member

    Hey guys...first post.

    I recently replaced motors in my 90 Ranger 4.0 2wd Auto. It was a 4.0 to 4.0 swap. The new motor has 80k miles on it. Truck fired right up after the swap but has a miss at idle and when just starting out (0-5mph). After about 5mph or 1000rpm I either can't notice it or it goes away. Until this point the ENTIRE car will shake and the engine looks like its loping, rocking back and forth, in the engine bay. If I take my foot off of the brake while in drive, I can feel the miss as it moves forward. I think this rules out mounts. After 5mph it drives great and has tons of power. No engine lights are on, and the truck passed smog running this way.

    I can take a plug wire off one by one and the miss will get worse each time. I cannot identify a lone cylinder.

    Things I have checked:

    MAF is clean and appears to be working fine.
    Idle control valve is clean and working.
    Changed fuel filter
    Fuel regulator is OK as far as I can tell.
    All cylinders 160psi compression.
    Replaced upper and lower intake
    Replaced all vacuum lines.
    Replaced spark plugs and wires.
    Checked rocker arms, rods and valves. All look brand new.
    Lifters appear to be fine.
    Ran seafoam through intake lines, gas and oil.
    Ran B-12 chemtool through gas.
    EIS is firing fine.

    I am out of things to do...Im clueless.

    Could it be fuel even though it runs great above 5mph? No hesitation or loss of power through redline.

    I bought the motor from a salvage yard. Could it be that the motor came from an explorer rather than a ranger? It is the SAME motor. If it was from an explorer could it be a computer issue? Shifts fine.

    Pulled the plugs today. All but two look like they have little specks of pepper on them. Detonation? Why all of them? From the injector cleaners?

    Last edited: Aug 5, 2010
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  3. Hooligan

    Hooligan Rangerholic!!

    Thread moved to the new 4.0 engine tech section
  4. DiabloBlanco

    DiabloBlanco Those Damn Kids

    throwing any codes?
  5. Black mamba

    Black mamba The mannnn

    Hey buddddyyyy, my 4.0 did this for a while I re~gaped my plugs to exactly.045 and it stoped... I also switch to motocraft plugs
  6. Brinker88

    Brinker88 Black sheep o' the family

    Same year 4.0? Also, did the donor truck have the same tranny? If not, maybe the computer is reading that it has a different tranny and its throwing off everything else....just thinking out loud here. What about the coil?

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