1997 Explorer No start possible fuel system problem

A '97 Explorer with this problem:

Over the past year, the car might not start after starting well for months at a time.

First and second time, replacing the Fuel Pump Relay would seem to solve the problem for a few months.

Currently, no start condition. Tested the following:

1 Spark to plugs is OK

2 Fuel pump relay tests OK

3 PCM power relay tests OK

4 Voltage to power distribution box (fuel pump relay) is 12 volts

5 Inertia fuel shut off switch tests OK and has power coming to it

Do you have fuel pressure?

I don’t know if it has fuel pressure. Havn’t tested it yet. Don’t hear the fuel pump when ignition is first turned on so I assume that the fuel pump isn’t getting power.

No fuel pressure. (It can’t start so there is no way of knowing what the continual pressure is. No pressure at the pressure test port.)

I have the factory wiring diagrams for all my Fords, including my 97 Explorer.

Not much to the fuel pump circuit.

The PCM is wired to the inertia switch & from there to the fuel pump.

You should see 12 volts at the inertia switch for 2 seconds each time you turn the switch from off to run.

You say that you do have voltage at the inertia switch, so try this simple little test: give the fuel tank a good whack with your hand. Now turn the key one click. Does the pump run?

This little trick has brought a dead pump back to life & gotten me home a couple of times.

OOPS MY BAD, i was going from memory & a 97 Explorer is NOT wired as I mentioned above.

The coil side of the pump relay is wired to & triggered by the PCM.

Switched side of relay is wired to the inertia switch.

Bottom line is if you have power to the inertia switch, the pump or the wiring between the inertia switch & the pump is the problem.

Like I said, give the tank a whack & see if the pump runs.

Well then, if you have power at the fuel pump connector (over/by the tank), it would have to be a bad fuel pump.

Each time the ignition switch is turned to RUN, the fuel pump is powered for 1 to 2 seconds, only. As long as the engine is cranking (or, running), the fuel pump is powered.
You could disconnect a fuel line, aim it into a catch container, and turn the ignition switch ON and OFF, several times. Fuel should push from line. If not, troubleshoot fuel pump circuitry. http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Wiring+Diagrams&partName=Chassis+Electrical&pageId=0900c1528018efd2&partId=0900c1528018eeda

Do you have the old relays? Do they work when you bench test them? If not, something is burning them out and that is most likely the fuel pump going over current because it is not spinning well. Maybe it is worn out or you have a fuel line restriction. I guess you have replaced the fuel filter. There may be a screen in the tank that is clogged. If the old relays work, I would check the relay socket.

If you suspect a fuel problem try spraying some starter fluid into the intake and see if that gets the engine running.

He’s confirmed that there is no fuel pressure. I see no reason to do this test.


I would think the vehicle ought to be scanned to see if there are any codes pertaining to something in the system which can cause a no-start condition. There are codes pertaining to fuel pump circuits, ignition circuits, etc.
It could even be an ECM fault (lack of ground for the pump relay)

Replacing the fuel pump relay multiple times smacks of wild guessing and more than likely the fact the problem appeared to be resolved for a few months is sheer coincidence.

The fact the OP can’t hear the pump when the ignition is first turned on does not necessarily mean there is a lack of power to the pump. It could be the pump dying.
Think of a cabin blower motor that does the same thing.

It is not uncommon for failing fuel pumps to draw excess current while they are on the way out. This excess current can weaken fuel pump relays. As a result, replacing a fuel pump relay can allow to pump to live for a little while longer. I don’t think this was a case of guessing. It was a case of not getting all the way to the root cause.

Thank you all for your responses.

Here is where we are now.

  1. No OBDII codes from scanner.

  2. No fuel pessure from test fitting when turning power to “on”.

  3. Starter fluid is only thing that burns when sprayed into “air cleaner”.

  4. All relays (3 so far have tested OK.

  5. Fuel tank is 3/4 full.

The next thought is that there is an intermittent short under the “power distribution box” which may be the reason that a “good” relay fails to initialize the pump. Putting a new relay in puts pressure on the distribution box which completes the circuit for a few months and then the “short” opens again.
Does anyone have a list of how to pull the “box” and test for an open?

thanks again.

You haven’t answered the question, yet, "Do you know, for a verified fact, that a dirty fuel filter isn’t dropping the fuel pressure to near zero?"
Here are the wiring diagrams for the fuel pump. http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Wiring+Diagrams&partName=Chassis+Electrical&pageId=0900c1528018efd2&partId=0900c1528018eeda Scroll way down to Fig. 34, or Fig. 35, or Fig. 36 (depending on which engine your Explorer has). To make the image large enough to read, go to View (in the upper left hand corner of your pc), and use the Zoom In 6 times.

You did not state which engine you have but assuming it’s the 4.0 you might check this if you have a test light or VOM.

With the key in the RUN position the red wire at the pump relay should have battery voltage.

When the key is first turned to the RUN position the light blue/orange lead should show a ground (through the ECM) for a couple of seconds. After the 2 seconds the ground will disappear.

This ground will reappear when the engine is cranked over by the starter motor or is running.

This ground circuit is an electronic one generated by the ECM and it’s not unheard of for this ground to disappear permanently or come and go. This ground is also helped along by input from the ignition module but if this signal was not present there should be a code set.

In line 5 of the original post by OldGuy he states that there is power getting to the inertia fuel switch. He dosen’t state if the voltage is getting past the switch with the load on it but did state it tested ok somehow. Looking at drawing #35 that Hellokit provided a link to shows this switch is the last thing in the circuit before the pump. So if power is getting to that point and perhaps through the switch also then the wire connection to the pump from the switch may have an intermittent problem, the pump motor is faulty, or the pump ground is intermittent.

Going from your statements about the fixes in the past leads me to think you got close to the real trouble but didn’t really find it yet. This trouble sounds like a bad connection (or possibly bad pump motor) somewhere between the inertia switch and the pump ground. 87 Ranger stated the same thing in his post. The possibility of the pump relays going out due to excessive current being drawn by the pump motor as Tardis mentioned is a real good thought I think but if voltage is truely getting to the inertia switch under load then it seems the pump relay contacts would have to be ok.

Latest update:

  1. Relays test OK

  2. Getting power to inertia fuel switch and continuity between line in and line out (to black/pink) wire.

  3. No fuel pressure.

  4. 3/4 tank of gas.

This leads to one of two conclusions.

  1. Bad pink/black wire to fuel pump connector OR

  2. Bad fuel pump.

Unfortunately, the pink/black wire from the inertia switch to the fuel pump connector “doesn’t exist”. Pulling the connector, there are only 3 pins going out, (and about 12 wires leading into it). None of the wires looks like pink/black.

Does anyone have a color schematic of what the wires going in to the connector are and where the 3 pins going out go to?

Did you check the wire colors at the pump to see if they match any of them at the connector you mentioned? It seems one at least should match.

You should also check to see if any voltage is getting to the pump and could also try applying 12 volts to the pump directly to see if it works.

I’m trying to avoid dropping the tank. The car is in my garage and trying to pull the tank would be a real pain.

There appear to be only three pins that go thru at connector on frame rail.

The two "outside pins appear to receive 6 volts when the ignition switch is turned to “on”

If I knew what the 3 pins were supposed to connect to it would make it easier to diagnose.