I’ve got a 1992 Ranger XLT 3.0. I replaced the Fuel Pump, filter, & relay but it still won’t crank. Inertia switch appears to be good. Resets just fine and isn’t, sticking or tripping off. After trying some info online about diagnosing I removed the relay and jumped a wire from terminal 3 & 4 together. The fuel pump kicks on and engine runs fine but the fuel pump does not shut off. Found some info about getting trouble codes using the check engine light. Best I can tell it is showing code 556 (Fuel Primary Relay Primary Circuit Fault). I’ve looked everywhere on how to diagnose this problem which is how I found the Ranger forum.
Electrical trouble shooting is my weakness. I have an Ohm meter and a test light but now I’m in need of some help and an explanation on how to find the problem. Thanks in advance for any help.

 

Welcome to the forum


556 (O,M) Fuel pump relay primary circuit fault - Power / Fuel Pump Circuits

The primary circuit referrers to the Fuel Pump relays activation circuit, not to fuel pump power

A relay has two parts
A coil(literally a coil of wire), it needs 12v and ground, that turns the coil into a magnet, which activate the other part

Other part is the Load, basically inside the relay is a metal bar, a spring holds it up, when the "coil/magnet" is activated the metal bar is pulled down which makes a connection between the 2 load contacts, sending power to the device the relay is connected to, in this case the fuel pump
When you did the jumper wire you were connecting the LOAD contacts together



The fuel pump relay's coil should get 12volts with key on, but the Computer controls the coils Ground so it can turn it on and off
Computer should "see" 12volts on that ground when key is on, because its is just a coil of wire, so 12volt on one end of the wire will be 12volt on the other end at the computer
If computer does not see that 12volts then it will set code 556

So for testing pull out the relay and set Volt Meter to read DCvolts
leave key off
Test each slot in the relays base
Should only be 1 with 12volts, thats from the Fuel Pump fuse, for fuel pump power, so 3 or 4 according to you

Now turn key on
There should now be another slot with 12volts, if not there's the problem
If there is 12volts on another slot then the relay is most likely bad but..................hold on

Look here: https://www.therangerstation.com/tec...ry/OBD_I.shtml

In the engine bay you will find the OBD1 plug, looks like 2nd drawing
In that drawing Fuel pump slot is labelled
Put fuel pump relay back in
With key on that slot should now show 12v
Turn key off
That slot is connected to computers ground wire for the relay, pin 22 on computer
Use a jumper and GROUND that slot
Turn key ON
Fuel pump relay should click closed and fuel pump should be on
If so then wire to pin 22 on computer is bad



If Relay slot did not have the 2nd 12volt slot then its wire from the PCM(EEC) relay is bad, its a red wire on the relays base, it can get corroded and quit working

 

Removed the relay and with the key OFF only slot #4 showed 12v.
With key ON only slot #2 showed 12v.
According to your instructions that would mean it’s a bad relay. I replaced it, and it didn’t help.

When checking the obd-1 plug fuel pump slot
I get less than 1v with both the old & new relay.

After this step you said to use a jumper and ground the Fuel Pump slot on the obd-1 plug.
I’m not sure how to do this. Please explain.

 

Well if you only saw 1v on the Fuel pump slot in OBD1 connector then that "ground" wire is broken or corroded at the Relay base, and thats the problem

You will need to look at the under side of that relay's base and maybe replace that wire connection

In a 1992 Ranger with 3.0l is the Fuel pump relay IN the engine fuse box or under the engine fuse box?

In some early 1990's it was like this: https://www.2carpros.com/forum/autom...2900_fp_12.gif

But I think the 3.0l had relay in the fuse box?


Key on 12v-----------------relay coil-----------------------obd1 slot--------------pin 22 Computer

So with key on you should see the 12v passing thru the coil and show up at OBD1 slot, and you don't, computer should also see that 12v and doesn't so sets code 556

So between the relays coil connection and the OBD1 slot the wire is damaged or corroded, its not a long wire, and usual suspect is the relays base connection

And yes if you were to Ground that OBD1 slot the relay coil would close the relay and power up fuel pump, but that won't work now because that wire is not connected well enough as seen by the 1v

Why is grounding that OBD1 slot not a SHORT since it should have 12volts!!!

Shorts happen when there is no LOAD on a circuit

For a light bulb to work it has 12v and a ground
12v---------------bulb-------------ground

If I did this
12v---------------bulb----------volt meter--------ground

Volt meter would show 12v because bulb is just a coil of wire in a vacuum, and if I ground it again, no short..........light bulb just lights up because its a LOAD

Same for the relay circuit, relays coil is the load, but you should see the key on 12v on its Ground side IF the ground side wire is OK

If you connect a wire from 12v to ground with no LOAD then there is a SHORT because there is nothing to SLOW DOWN the electrons/AMPs, so wire gets REAL HOT and you have a short and maybe a fire, lol
A LOAD slows down the flow of AMPs, limits it

 

Yes, on my ‘92 Ranger the relays are under the fuse box. They are very difficult to get to even if you unscrew the fuse box from the side of the engine compartment. There is hardly any slack in the wiring harness. I was very careful when removing all of it because it’s 28 yrs old and all of the wires and plastic feel stiff & brittle. I was afraid of creating a short but it sounds like I have one anyways. Speaking of which, I tried to find some info or a video on how to repair the wire and/or connector on the Fuel Pump relay. Any advice on where to look. I tried Google & YouTube but haven’t found any thing on the Ford type relays. Thanks!

 

Fuel pump relay should have a green color base
EEC relay Brown
WOT relay black<<<(only there if you have factory AC)

Ford used two different kinds of relay

Standard(most common) automotive relay looks like this: https://www.gtsparkplugs.com/images/...iring-840x.jpg

But Ford also used this kind as well: https://www.gtsparkplugs.com/images/...lay-wiring.jpg

These are 5-pin relays, because they have 87A, both the above also come in 4-pin, so no 87A, which is not needed in most applications

pins 85 and 86 have no polarity, either can be 12v or ground, as long as there is BOTH, a 12v and a ground, relay will activate(close) and connect 30 and 87 together

30 and 87 also do not have a "direction", its just a switch, on or off, it either passes power, ON(30 and 87 connected) or cuts power, OFF(30 and 87 not connected)
So either can be the 12v and the other connected to Fuel pump, in this example

For 1992 fuel pump relay wires
Black/yellow stripe should be 12volts from Fuel pump Fuse(30 or 87)
Dark Green/yellow stripe goes to inertia switch(12v to fuel pump)[30 or 87], may be 2 wires of same color connected here

Red wire, key on power for the coil(85 or 86)
Light Blue/orange stripe, ground for coil, goes to OBD1 connector and Computers pin 22(85 or 86)

Most automotive parts stores sell relays with bases, you need 12v 40amp rating relay

 

I found another forum thread on here that said to remove the FP relay and jump #3 & #4 slots together to manually activate the Fuel Pump.
IT WORKS! The engine cranks right up and runs good. But, the fuel pump never shuts off. According to that post it says that means the FP & inertia switch are good and that the wiring from the pump to the relay is good. Does this change anything from earlier or do you still believe the red wire at the bottom of the FP relay is bad? I’m trying to figure out how to open the relay connector without breaking it so I can clean or fix the terminal before resorting to cutting it off and replacing it. The wires are so short there isn’t much to work with. Any way of confirming it’s bad with a test light?

 

Slots 3 and 4 are 30 and 87, so yes jumping them sends 12volts to fuel pump full time

Your issue is not 30 and 87

Your issue is with 85 and 86, you said slot 2 had 12v with key on, thats either 85 or 86 and thats the RED wire, so red wire is not the problem

Problem is the Light Blue/orange stripe wire which is suppose to be the GROUND for the relay, this activates the relay so 30 and 87 are connected, like the jumper wire does

The Light Blue/orange stripe wire runs to OBD1 slot which only showed 1v with key on and relay plugged in, should be 12v, so that means this Light Blue/orange stripe wire is not fully connected to Relay.....slot 1?? maybe

The Coil circuit, 85 and 86, is very low AMPs, under .5amp
So if you want you can insert a small wire into Slot 1 on top side of base, then plug in the relay to hold wire in place, then Ground that small wire
With key ON the relay should now click closed and fuel pump will be on
And then be off with key off

This is a temp fix, you are "hot wiring" the ground