Toyota 4Runner:

Toyota 4runner, 1988

Hey motocross116:

I'm an off-roader -- XR400R -- getting old, but bulletproof and lots of fun.

Fuel pump circuits are wired differently from truck-to-truck, but the basics almost always hold true.

Turn the key on and the ECM will run the pump for 2 seconds to prime the system (then shuts off). The pump will run continuously while cranking, and once the ECM sees an RPM signal (the engine running) it will keep the pump on until the engine shuts off.

Voltage and ground to the pump while cranking, but the pump does not run, means you need a pump.

Missing voltage or ground to the pump while cranking, means there's a circuit problem which needs to be investigated further.

You know we don't believe in just swapping parts.

Keep in mind that you should be testing all circuits before replacing anything.

Your old Toyota is a little different than most. There's a main relay, a circuit opening relay (fuel pump) and an air flow meter which applies the relay when sufficient air flow (RPM) is present. (see schematic).



You should start at the pump and work your way back with a test light.

And bypassing a fusible link is a little scary -- that's how fires start.