Check for stains on the bottom of the fuel tank. If present, suspect the seal is mispositioned or the lock ring is not tight on the new fuel pump assembly. My guess is this is not the problem because even though you might smell the fuel, you would have to overfill the tank to affect fuel mileage. The evaporation would not be noticeable as far as fuel mileage is concerned.
Also check for dripping fuel ahead of the right rear tire. If you find that, a fuel line is rusted through and leaking or the connections are loose on the filter. Except for diesel engines, you will never solve a running problem on a Chrysler product by replacing the fuel filter. Often the fuel leakage results from the filter's hose clamps rusting off. When this happened many years ago on my '88 Grand Caravan, I found one clamp completely gone, one split apart and leaking, and two that I twisted off with a small pliers. There's almost 50 pounds of fuel pressure, so it was amazing it didn't start leaking sooner due to the missing clamp.
When the same thing happened on my mother's '95 Grand Caravan, 20 bucks worth of gas barely got me the 12 miles to home! In this case, most of the fuel will be lost while driving. When you stop the engine, fuel will only leak out until the pressure is bled off. Although the puddle could be very big, the actual amount of fuel spilled will be just a few tablespoons.
The last place to look is where the fill pipe goes into the tank. There's a rubber gasket there that could be deteriorated. On some models, that pipe inlet is about halfway up the side of the tank.
If the fuel mileage is affected as much as you say, there has to be some evidence of it somewhere. I would take it back to the place that installed the pump. Most shops warranty their work.
Saturday, June 20th, 2009 AT 3:15 AM