Ford Taurus 2001 3L V6 Engine; Non-starting problems
In this example Power Probe show us how to quickly solve a non- starting Ford Taurus by using the Power Probe IV while following the basic steps of a non-start diagnostic chart.
Starting out
The first step was to verify and identify the customer’s concern. When we attempted to start the vehicle it would crank but wouldn’t start, so our next move was to then verify that the inertia fuel shut-off switch was pushed in; the inertia switch is a safety item that cuts power to the fuel pump in the event of a
collision. After locating the switch we were able to confirm that it was.
Our next step was to then check for a spark. To do this we installed a spark tester to a spark plug wire and cranked the engine over – we had spark. However, when we turned the key on before cranking the engine over we didn’t hear the fuel pump coming on, so our thoughts turned to checking the fuel
pressure.
With a fuel pressure gauge installed to the test port and the key turned on/engine off we got no fuel pressure at all, even though a normal reading for this engine should be between 35 and 65 psi. Since we didn’t have any fuel pressure we now needed to see if there was any power going to the fuel pump.
Looking at our schematic diagram (see below) we recognised that we could test the fuses, PCM power relay, fuel pump relay, PCM and inertia fuel shut-off switch by back probing the #2 terminal of the inertia switch and turning the key to the on position.
As expected, we saw battery voltage displayed on the Power Probe for one second (due to the PCM grounding the fuel pump relay) and this told us that all the components and the wiring leading up to the inertia switch were good.
Our next diagnostic step was to check the voltage at the fuel pump harness connector, but this was located underneath the vehicle. Since the Power Probe 4 has the ability to supply battery power or ground to test components we simply disconnected the connector at the inertia and supplied power to
the #2 terminal to see if the fuel pump operated (see below). We couldn’t hear the fuel pump coming on and were able to verify this by looking at the fuel pressure gauge.
Pump problems
At this point we were pretty confident that we had a faulty fuel pump, but still needed to verify this by checking its resistance. Because we knew the resistance specifications of the fuel pump we could use the Power Probe 4 in ‘feed test’ mode to check the resistance of the fuel pump at this connector.
The feed test mode utilises the tool’s ability to be connected to the vehicle’s battery, which allows us to check the resistance of a component directly to ground.
We probed the #2 terminal of the inertia switch and got approx. 1.2 ohms of resistance, which was well below the specifications of 8.5 – 15.5 ohms. With such low resistance it was very possible that the windings inside the fuel pump had been shorted together and that we had a faulty fuel pump. After replacing the pump (see below), we attempted to crank the vehicle and it started. Job done!
