1998 Chevrolet Express

Engine Performance problem
1998 Chevy Express V8 Two Wheel Drive Automatic 121500 miles

My 1998 Chevy Express 1 ton 3500, with a 5.7 liter engine began stalling last week. I traced it to worn conducting spark plug wires. Upon changing them the van ran fine again. However 1 week later I experienced ignition cut out again. This time I traced it to the brittle wiring that paralleled the 5/8" heater hose going to the van's on board PTO driven ( driven from the van's engine) Steam Genie Carpet cleaning machine. As an anti-theft deterrent Steam genie installed a switch on the transmission linkage so that when the vehicle was shifted out of 'PARK' it would interrupt the ignition coil 12v+ supply.
So today after discovering the faulty wiring I basically removed all 4 wires from the theft system and simply reconnected the original 12v+ to the coil, back to factory OEM. Upon making the change I discovered that the fuse to the e.C.M. Blew. Fine, I changed it, but now the van would run for anywhere from 30 seconds to 3 minutes and then the spark would disappear. Mind you none of the theft stuff is anywhere in the picture now. Frustrated I went ahead and installed a known working ignition module and coil from another identical van. I was able to drive several miles with a top speed of about 50mph- actually the speed limit was 50 mph and it was in a speeding ticket area so I couldn't exceed 50 anyway, but just the same it ran like it was dogging out a little. As I slowed down the van began to stall so I two footed it the last mile home, stopping at lights and stop signs while revving the engine. After getting in my driveway I pulled the cowling back and watch the engine die. After positioning the coil plug wire so I could observe the firing I restarted the van. The spark was very strong, though yellowish more than blue. Regardless, with no warning the spark disappeared. I restarted it. It would maybe run for 30 seconds, or a minute, but not the longer period like it did before when I was able to drive it up to 50 mph for 10-12 minutes.
One thing I did not do was disconnect the negative from the battery to reset(?) The computer.
Something else I should mention is the fact that somewhere along the way early on today when all of this began I lost power to the fuel pump. Obviously the circuit in the computer that turns on the pump shorted out. So like I've done on several vehicles in the past, I simply ran a new wire to turn on the fuel pump. Never have any other cars, trucks, or vans that I have done this to in the past have had extra issues stemming from this type of repair. I'll call it a repair- maybe not a 'proper' repair like the certified mechanics are trained to uphold. I mean after all would you want it to be your neck if a car caught on fire in an accident because that obviously very touchy fuel pump relay circuit from the computer was bypassed to save the customer $500+ for a new computer. It's not like I'm cheap, but my goal right now is to fix this so that I might be able to actually clean carpet for the next few days. THEN I'll worry about buying a computer.
I do appreciate any real help. Lectures I'm not up for. Thanks.
October 16, 2009.

Check out the related content below while we wait for the question to be answered by a professional mechanic.