Strange fuel relay issue 87 ranger - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 05-31-2014
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Strange fuel relay issue 87 ranger

I've gotten everything finally going on this truck except one issue with the fuel relay. Everything worked with the relay jumped, jumped the 1 and 4 terminals together and the 2 and 3 terminals together, which makes the fuel pump constantly run.

So I got a new relay and it was just cranking, I took the relay back off and noticed it have 5 terminals and the old one had 4, so I thought that might have been the issue. All of the fuel relays i've found for this truck have 5, even though every picture or anything you find of one is a 4 terminal relay, but I found a multi purpose relay that had the same 4 terminals, that one also did not fix the issue...still runs while jumped.

Then I discovered that if I only jump the 2 and 3 terminals without jumping the other two, the pump only comes on when I turn the key on and start it, so I can keep it like that for now. But is it supposed to be doing that? If not what could cause it? Why won't any of the relays I've gotten work? And should I be using the 5 terminal one or the 4 terminal one? Any help is greatly appreciated!
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Old 06-01-2014
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you clearly have battery power being fed to the relay

the problem is that the relay is NOT being triggered by the ignition switch

dis-connect the negative battery cable , unbolt the fuse panel and pull it out , you are looking for corroded fuse connections--specifically the fuel pump relay trigger fuse
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Old 06-01-2014
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The 5 terminal relays are standard now and are fine to use for replacements, if they fit into the older base/socket.

here are the power paths for the fuel pump system:
battery----------fuse(fusible link)---------fuel pump relay-----inertia switch------fuel pump-----ground

Above is fuel pump power, now relay power:
Battery-----EEC relay------fuel pump relay--------computer(PCM)-------ground

Here is a diagram of a standard automotive relay:
Free ASE Study Guides: Automotive Relays

connections 85 and 86 will close(activate/on) the relay when power is passing thru, in the Ford system(and most others) connection 85 will have 12volts when key is on, but connection 86 will not be grounded so there will be no power passing thru.
These can be reversed, there is no direction requirement for power passing thru the relays "coil".
85 or 86 should show 12volts when key is on, that means EEC relay is sending power to this relays "coil"

30 and 87 are the LOAD connections for the relay, this is where the high amp voltage for the Fuel Pump passes thru when relay is closed(activated/on).
87a is that 5th connector, it can be used to pass power when relay is open(off).

30 will be connected to the battery/fuse and have power all the time
87 will be connected to the inertia switch/fuel pump
These can also be reversed in this application since 87a is not being used.

It reads like you have voltage at all the correct places, but computer(PCM) is not grounding the relays coil(86) when it should.
I would test the voltages just to be sure.

The Light Blue/Orange Stripe wire coming out of the relay base is the "ground" wire that runs to pin 22 on the computer.
The computer has a few Ground wires around it that need to have good clean connections so it can use them to ground things like the fuel pump relay and fuel injectors.
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Old 06-01-2014
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Ok, so I need to check the ground wires, if they seem all good do you think the pcm could be bad? Thanks for taking the time to help!

Edit: It seems I made a mistake on originally jumping the relay, I connected 30(12v) to 86(ground) I remember when I did that I heard a click that sounded like a relay (fuel pump relay was not in since I was jumping) is there anything to prevent the computer from frying if that were to happen, like a secondary relay or fuse?

Last edited by Phillfxc; 06-01-2014 at 01:17 PM.
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Old 06-01-2014
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No, you should be fine, pin 22(PCM) will have 12v when key is on, because the relay "coil" (85/86) is just a wire coiled around a metal bar, so 12v in/12v out.
When the PCM grounds pin 22 internally, the 12volts flows thru the "coil" so it turns into a magnet and closes/connects contacts 30 and 87.
Yes, it could be internal PCM problem.

The fuel pump runs while engine runs.
The normal PCM control is for safety reasons.
Normal operation is when key is first turn on the PCM will ground pin 22 for 2 seconds, this is to prime the fuel system/pressure, it will not be turned on again until RPMs are above 500.
Reason for this is in case of an accident, if fuel system lines break and key is on then fuel pump will just keep pumping out fuel, if rpms are below 500(stall) the fuel pump would be off, if there was a break in the fuel line engine would also stall from lack of fuel so fuel pump would go off.

There is also an inertia switch that is there for the same purpose, fuel pump power passes thru this switch, inside it is a weight, similar to seatbelt weight system.
In the event of a sudden stop, accident, the weight is moved quickly in one direct and breaks the power contact inside for fuel pump(it has a reset button) so power to fuel pump is cut, same as seatbelt weight holds seatbelt from extending when there is a sudden stop.

Electric fuel pumps have that one draw back, in an accident they can feed a fire if they don't have an automatic shut off.

So while it is best to find the problem you could ground the Light Blue/Orange Stripe wire so fuel pump comes on with the key, it doesn't hurt anything, except safety aspect

Last edited by RonD; 06-01-2014 at 01:45 PM.
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Old 06-01-2014
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Alright, I am definitely getting voltage in the right places, so it seems like it's just not grounding when it should be. I'm going out to check the grounds around the computer in a few minutes, I'll see what I've got and update :)
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Old 06-01-2014
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There is a VIP connector in the engine bay, on Rangers it is often on drivers side near firewall but can also be passenger side.
This is a diagram of the connector: DIY KOEO/KOER/Cylinder Balance Self-Test Procedure

If you scroll down you will see it.
Fuel pump Trigger is the port you want, that is spliced to the Light Blue/Orange Stripe wire from relay and pin 22.
If you ground that port, and key is on, fuel pump will come on, this will test if relay is working with ground control.
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Old 06-01-2014
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Well there was one ground coming from the pcm, the only thing I saw was that the part of the body that it's grounded to was painting, so I sanded that off and cleaned it up real good. No change though. The only things left that could keep it from grounding would be the connection to the relay, and the wire itself right?


Edit: jsut saw your post I'll check it out
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Old 06-01-2014
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Found the VIP connector...nothing is plugged into at all, It's a red female plug shaped the same as the pictures
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Old 06-01-2014
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I grounded that port on the VIP connector, started right up and ran, not sure where to go from here

Edit: would this mean the wire from the VIP to the pcm(pin 22) is bad? or perhaps even pin 22?

Last edited by Phillfxc; 06-01-2014 at 03:14 PM.
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Old 06-01-2014
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Grounding VIP "FP" port and fuel pump starting means wiring at FP relay is OK.

You can check voltage at pin 22, should be 12v with key on("FP" port not jumped)
This would mean wire to PCM is OK

Here is a pin diagram of EEC-IV PCM, used '83 to '95:
ford eec iv

Good page to book mark

Light Blue/Orange Stripe wire should be at pin 22.
I like to use sewing pins to pierce wires to test Volts and Ohms, just make sure sewing pins can't short to ground or each other.

Last edited by RonD; 06-01-2014 at 03:33 PM.
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Old 06-01-2014
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Alright, need to go to my buds to borrow his voltage meter, So if I'm getting 12v at the wire going into pin 22 then the wire is good and pcm/pcm ground is bad? and no or low voltage means the opposite?

Thanks so much for the help again, not only are you helping me get this truck going again, I'm getting a much better understanding of how this works

Last edited by Phillfxc; 06-01-2014 at 04:02 PM.
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Old 06-01-2014
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Yes, 12v at pin 22 would mean wiring is good.
And for some reason computer(PCM) is not grounding that pin when it should.

Engine runs with FP jumper in place, if you remove jumper after engine is started does engine die?

If so then with all the other stuff tested I would say PCM is the problem, it is just not that complicated of a setup, lol.
Just that darn off/on switch inside the PCM.

On the PCM pin diagram are a few Ground wires listed, you could also test those, to make sure they are grounded.

If you have 12v at pin 22 then you can use that on the Red Meter probe, and then use the Black meter probe to test each of the 5 PCM grounds(0v), or use OHM meter to test each Ground to a Cab ground, should be 0 ohms(dead short)

Last edited by RonD; 06-01-2014 at 04:41 PM.
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  #14  
Old 06-01-2014
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Yup dies as soon as soon as it's removed. Alright then, I'll test that wire and if it's good I'll check for continuity or corrosion at the plug, and replace what's needed. Thanks for all your help man, should have it sorted out soon :)
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