Fuel pump wont run, ECM code 12 repeats

I have an 88 C1500 Silverado with 350 and 700 R4. The fuel pump will not run. I have dropped the fuel tank, removed and bench tested the pump and it worked fine. Put the tank back in, replaced the fuel filter, fuel pump relay, oil pressure switch, and still nothing. The ECM codes read 12, and repeats 12's as long as the ignition switch is on. The only thing I can determine is that the ECM is stuck in diagnostic mode.

Any suggestions or past experience with this problem would be greatly appreciated.

Ed

Code 12 will always show up on your truck. Thats normal. It doesn't mean anything is wrong.
There might be a fuseable link for the power to the fuel pump. Might check that out. Also, does the fuel pump relay get power when the key is on?

did you check fuel pump fuse far left of relay also to check fuel pump you can attach a fused 12 v powered jumper to terminal G bottom left terminal of code reader port under dash and have somone listen at filler for pump to run

When my fuel pump failed, it worked...meaning you could hear and see it running.But when pressure reading was taken it barley put out 12 pounds of pressure. Even though it sounded like a normal heathy pump motor, could not give the volume and pressure required to keep running.You need something like 60-70 lb of pressure