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surging under load

I have a 1994 dodge ram 2 wheel drive with a 318.

Idles fine but when put under a load it starts surging and bucking at about 1500 rpms.

Idles at 1500 no problem only under a load...
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Comments

  • edited April 2011
    Well, since you said almost nothing that would help anyone even get started all you're going to be able to get are wild guesses all over the map.

    Give it a new set of plugs and wires. Is this distributor based or a coil pack? Give it new fuel and air filters. Clean out your throttle body. Check the fuel pressure - under load. Put a vacuum gauge on it and check for evidence of exhaust blockage. Is the check engine light on? Is this a manual or automatic? Howe many miles are on it? Are you actually saying that it routinely idles at 1500 rpm? Too high. Look for vacuum leaks & pay special attention to the MAP sensor & its connection @ the manifold.
  • edited April 2011
    Sorry 200,000 miles new plugs and wires cleaned all the sensors, coil pack does not surge when idling or does not surge in park at 1500 or above rpm's.
    Only under a load and when the rpm's reach 1500-1700 or above it starts surging and bucking.
    I figure fuel pump, but would hate to buy one and not solve the problem.
    How many pounds of pressure does the fuel pump need to put out and is it different under a load?
  • edited April 2011
    no catalytic converter on the truck either....
  • edited April 2011
    I don't know the fuel pressure specs. You can probably find them along with a basic testing procedure at Autozone's website. If you register & plug in the vehicle info they have free repair guides. The pressure has to be maintained within a fairly narrow range. What changes under load isn't an increase in pressure - just a change in supply rate and the pump has to be able to keep up.
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