I'm working on my room mates1989 Ram 3.9 liter truck.
No fuel pressure on fuel pressure gauge during cranking or when ignition switch is in run position. Measured battery voltage at fuel pump relay coil wires with key in run position and it was fine. Applied battery voltage to "Green wire with black stripe".(Voltage supply wire to injectors, fuel pump, ECM etc?) But no pressure on gauge in run position or during cranking. Measured 3.4 ohms resistance at "Green wire with black stripe" with fuel pump relay disconnected and key off.
I measured 14.5 PSI on fuel pressure gauge when it was running last week.
He has been using starting fluid for the last several months to get it started most of the time, but even that won't work now. He also told me that he got a hefty fireball from the TBI assy when he used more starting fluid that normal the other day.
I replaced the oxygen sensor recently and engine coolant temp sensor because it was out of range with cool engine and warmed up engine.
I'm not a professional mechanic, but I have been doing repairs since the mid 70's. I'm an ex-Navy technician and I'm pretty good at troubleshooting.
This one has me stumped
I almost forgot. I read something online about another relay in the fuel pump circuit (inertial relay?). I forgot the name of it. The wiring diagram in the Chiltons manual I'm using doesn't show it. I want to make sure I have logically isolated the problem before buying a new fuel pump.