I've noticed that if my battery goes bad, and I have to charge it, then the fuel pump will stay running while I have the battery charger on it. Does anyone know whats up with the circuit? Could it be a relay? Im sure I've replaced the fuel pressure relay before. thanks
Sean

 

There are two components that give power to the fuel pump, the fuel pump relay and the oil pressure switch. Here is a 1989 diagram that may be useful: ftp://ftp.diy-efi.org/pub/gmecm/manu...9-165v8MAF.jpg

Oil Pressure Switch
There are three wires going to this switch/sender. The tan wire (cavity A) is for the oil pressure sending unit and displays in the instrument cluster your oil pressure. The tan/white and orange wires have to do with controlling the fuel pump. When the tan/white wire gets power, it turns on the fuel pump. This tan/white wire is also controlled by the fuel pump relay. The oil pressure switch is normally open, no allowing power from the orange wire to the tan/white wire. When the oil pressure switch closes (reached a certain oil pressure threshold) the power from the orange wire is applied to the tan/white wire. If your oil pressure switch is stuck closed, and your battery has power, then the fuel pump will run.

Fuel Pump Relay
When the ECM sends power through the green/white wire to the relay, the switch closes and routes power from the orange wire to the tan/white wire. The orange wire is the same circuit as the orange wire for the oil pressure switch. The tan/white wire is the same circuit as the tan/white wire for the oil pressure switch and fuel pump.

If, when the battery is not charging (but still carries somewhat of a charge), the fuel pump runs, then I would say you have a bad oil pressure switch. In this case, when the battery has a charge, it is sending power through the orange wire to the oil pressure switch and because the oil pressure switch is stuck closed, the power is routed to the tan/white wire and turning on the fuel pump. Keep in mind that the orange wire goes directly to the battery through a 20 amp fuse.

The only other way for the fuel pump to run is if the relay turns it on. If the green/white wire or red wire is touching a 12v power source, then the fuel pump relay will close the switch and route power to the fuel pump. Also, if the tan white wire (anywhere in that circuit) is recieving 12v power, then the pump will run.

 

thanks, I pulled a 10 amp fuse and got the pump to stop, then I put the fuse back in and it stayed off. I remember a year ago I had to replace the oil pressure switch because of this same problem, I can't believe its back! so I will try and figure it out, thanks for the info, I really appretiate it.