fuel pump electrical problem

[pctghost]

I have a 93 ranger 4x4 ext cab 4.0L V6. My son was backing it out of the driveway and it just shut off. I had driven it the two previous days and it ran fine. We replaced the fuel pump thinking that was it, but the new pump is not getting any power. I have been checking the fuel pump relay and during cranking i get between 10 and 12 volts on all the wires except the fuel pump relay control there it is 7.9 volts. When i jumpered the fuel pump it runs fine. I put starting fluid in the air intake and the truck ran for a few seconds. Thought that it might be the computer, so i pulled that and i cannot see any corrosion or burnt out spots anywhere. The only thing left that i have to check is the resistance of the wire between the relay and the computer. Any help would be appreciated, at my wits end.

 

[Rowdy Fitzgerald]

Have you checked the fuel rail for pressure?

 

[pctghost]

Didn't check the fuel rail because there is no power to the fuel pump without jumpering it.

 

[FritzTKatt]

Check the power wire to the fuel pump, it probably got corroded and has a current leak so the fuel pump won't operate. Might even just be the connection is corroded.

Check continuity from the pump back, at some point you'll have a messed up line. Also check for 12v at each of those connections.

 

[RonD]

The fuel pump relay gets its 12volts from the EEC relay located right next to it.
This is not fuel pump power, its the relay's power.
Computer controls the relay's Ground.
Fuel pump power is fused and on all the time, when relay closes this power is passed to inertia switch and then to in tank pump.

So for the relay part you have;
Battery------EEC Relay-------Fuel pump relay------computer-----ground

Fuel pump power looks like this:
Battery-----fuse-----fuel pump relay------inertia switch-----fuel pump-----ground

Key switch activates EEC relay, which supplies fuel pump relay with 12v, but it has no ground so stays open.

With key on you should have TWO 12volt contacts in the fuel pump relay socket.
With key off only ONE 12volt contact, that's the fused fuel pump power.

If the one that is switched on and off with the key is only 8volts then check EEC relay's power, also look for corroded cable.

EEC relay supplies 12volt to coil, injectors, computer, and many sensors and controls.
All these are spliced into the EEC relay's 12volt OUT wire at some point, these points can get corroded.

 

[pctghost]

The EEC relay to fuel pump relay is getting 12 volts when the key is on and the fused fuel pump power is getting 12volts all the time. The wire going to the inertia switch has no power when the key is turned on with the relay out. The relay control has 9.5volts of ground with the key on. The wires to the pump itself has 7.96 volts to the yellow and black wire and the pink and black wire has 5.48 volts. The black and black/yellow wire have no voltage with the key on.

 

[RonD]

Power for fuel pump is like this:

Battery-----Fuel Pump Fuse------Fuel Pump relay--------Inertia Switch-------Fuel Pump

So if relay is removed there would never be power at the inertia switch.
With relay removed you can use a Jumper wire, from the 12v(key off) slot to the inertia switch wire slot(dark green/yellow wire), you should then have 12v at both sides of inertia switch and fuel pump should be ON.

Fuel pump relay power is like this:
Battery-------EEC relay--------Fuel pump relay-----computer

Red wire on the relay socket is the 12v when key is ON
Light blue/orange wire on the relay socket is the Computer wire, it will only show as a ground for 2 seconds when key is first turned on.

There might be a test port under the hood, if so it should have a connection labeled FP(fuel pump), with key on and relay in place, if you use a jumper wire and ground the FP connection the relay should click and fuel pump should come on.
There is a diagram here:
http://www.therangerstation.com/tech_library/OBD_I.html

On the '93 I think this connector will be on the passenger side engine bay near firewall, but they did move them around

 

[pctghost]

I jumpered the fuel pump from the key on slot to the inertia switch slot and the fuel pump will cut on. Checked the fuel pressure today and it is at 40. Even with the fuel pump jumpered the truck still will not run. Did the test and the fuel pump kicked on.

 

[a31ford]

For what it's worth..... the power going TO the computer (the line the computer gets FP power from (there is more than one power wire to the computer) AND, to top it off if memory servers correct.... the computer grounds the relay NOT energizes it. (electronics have a greater "sinking" potential than a "supplying" potential).

I would check the connections that supply the relay with power, NOT the fuel pump power itself.

Greg

 

[pctghost]

The power to the relay is 12 volts on three connections with the key on and at one connection with the key off. The ground is only pulling about 9.5 volts.

 

[a31ford]

Well then I would say the following are the the three options to look at.

1) the inertia switch (under the carpet, passengers footwell, where the carpet meets the heaterbox.

2) the body to frame connectors fro the electrical going to the gastank (drivers inner wheel tub, drivers front fender, larger of 3 connectors mounted on the tub (look fo the large white wire having corrosion.

3) the wiring connector ontop of the fuelpump (at the top of the gastank)

I guess there could be a forth, the ECM harness connector to FP relay. I guess it could be possible that this wire has an issue.

 

[RonD]

I jumpered the fuel pump from the key on slot to the inertia switch slot and the fuel pump will cut on. Checked the fuel pressure today and it is at 40. Even with the fuel pump jumpered the truck still will not run. Did the test and the fuel pump kicked on.

An engine needs 3 things to start
Compression
Fuel
Spark

We will assume compression for now, since you haven't mentioned any oddness about engine cranking.

You have fuel, since 40 psi is plenty to start engine and keep it running for a minute or two, we can get back to this if engine starts then dies after a bit, there may be a common problem found when the "no start" issue is found.

Spark is now the unknown, '93 4.0l uses distributorless spark system.
So will have a coil pack with 3 coils inside.
Unplug its connector, there will be 4 contacts on the wire connector, 1 should have 12v with key on, it will be one of the end contacts, this 12v comes from the EEC relay as well, just like the fuel pump relay power.

If you have 12v at the coil, hook the wires back up and remove 1 spark plug, this is a double test.
Hook removed spark plug to it's wire and use jumper cable to clamp threads of spark plug and clamp other end of cable to a good ground.
Place spark plug so you can see it from the cab, through the gap under the open hood, crank engine.
Watch for spark and listen for compression "whoosh" from open spark plug hole, the double test.

If no spark, I think the '93 4.0l still had the separate EDIS6 module on inside of rad support or on wheel fender, it is black and will have a sticker with "EDIS6".
The EDIS module runs the coil, even if computer is not working EDIS would still spark the coil if it has power and a Crank Position Signal from CKP.
Good site for testing Pins on EDIS-6:
http://www.dainst.com/info/edis/edis.html

Now the common thread in all of this is the EEC relay, it provides power to pretty much all the engine sensors and controls via 1 wire that is spliced at a few points.

 

[pctghost]

I have 12 volts at the coil and I have spark. The inertia switch is not tripped, but I don't know if it is bad. The wiring at the fuel pump looks fine. I couldn't find the white wire on the fender well.

 

[pctghost]

Just as a followup, replaced the ecm and everything works fine now. Thanks for all the help.

 

[RonD]

Thanks for the update