2002 Windstar, P303 code

I just bought a 02, Windstar on E-Bay. The van was from a small car dealer in northern Indiana. The van was corp. owned. in Michigan. It seeded to have been maintained. The engine light is flashing and had the codes read with a P303. Plug # 3 is near normal, just looks wet (not firing). The van seemed to run OK at highway speeds but rugh idle at stops. I have a 3L windstar and this 3.8 seems to have about the same power. Could this be a major engine repair. It has Autolite plugs. I had the same code on my 3.0 with Bosch Platinum plugs. #3 plug had fauled. Changed plugs and problem solved. This seems to be different. Any sugestions would be apprecieated. Need to investigate this without spending a lot of time and money or should I just return the van? This would be my work van for service. Other minor issues, interior lights do not come on when doors open. Drivers and sliding door locks do not activate with power locks,

Cheap tricks!:

Remove the windschield cowling for better access ....

1. Switch the spark cables #3 and #4 at the ignition pack. Disconnect battery cable for five minutes and reconnect. Drive around a few miles. When the code comes back is it now P0304?

2. If not, lift the fuel rail and switch injectors on cyls #3 and #4. Disconnect battery cable for five minutes and reconnect. Drive around a few miles. When the code comes back is it now P0304?

3. If not, do a compression test on all cylinders.

.... report back.