Try disconnecting the vacuum hose from the fuel pressure regulator and plugging it. The truck won't run perfectly, and there might be some black smoke out the tail pipe, but if it doesn't stumble anymore, suspect a collapsing pickup screen in the fuel tank.
The screens tend to collapse when the largest volume of fuel is being pumped which is during coasting. Unplugging the regulator mimics loss of manifold vacuum as in when accelerating. Fuel pressure will go up significantly, hence the rich mixture and black smoke. High pressure is caused by the regulator becoming more restrictive, thus less fuel flows through it and back to the tank. The amount of fuel used by the engine won't change much, but there will be a lot less fuel going through the screen.
I don't think you can buy a new screen. You will either have to get a new pump assembly that includes the screen, or you can cut a slit in the top of it. The external filter will still trap dirt, but you also run the risk of jamming the pump impeller. Chrysler pumps are built to very tight tolerances. It makes them extremely quiet, especially compared to GM pumps, but they're also more susceptible to locking up. When you experience multiple pump failures, the fix is to have the tank steam cleaned to remove microscopic debris. Radiator repair shops can do that.
The screen could be plugged with a rusty-colored mud too. If so, try squeezing out the crud and washing the screen in clean gas.
When you drive with the regulator hose disconnected, the exhaust will be rich for a long time. This is hard on the catalytic converter. If this is the only way you can keep driving, don't plug the disconnected vacuum hose. Leaving it open will allow a little extra air in. Idle speed will be high, but there will be less chance of overheating the converter. The "Check Engine" light will also probably turn on after a minute or two. The engine computer will see the constantly-rich exhaust, memorize a diagnostic fault code, and turn the light on. Later, when the regulator hose is reconnected, the light should go off after you cycle the ignition switch off and back on. The fault code will be erased automatically after about 50 starts.
Friday, June 5th, 2009 AT 2:44 AM