1985 Ford F250 Fuel Pump Relay Wiring Diagram

Hey all, lets start with I am new to Ford trucks. I have a 1991 F150 Nite that has the Windsor and dual tanks. Truck has run awesome for 3 years. For the last 2 weeks, when i start information technology cold it would go up to 1200 RPM (normal) then immediately drop to 400-500 (sputtering) for virtually 1-2 seconds, then dorsum upwardly to 1200 normal. May non take anything to do with the real issue, but what the hell. Anyways, was driving and it just suddenly died. Inverse the fuel filter and fuel pump relay to no avail. Later establish the pumps are not turning on at all, fifty-fifty when switching between tanks. I hotwired the front pump, and it ran bang-up and shot gas out the filter I had disconnected. I checked the inertia switch, and the switch had full continuity through it (red button was non popped upwards) and the harness had 6.9V up one wire when disconnected (is this normal?). I tapped into the thick red wire coming out of the fuel pump relay, and I get full 12V when I turn the key, dorsum to zippo when turning the primal dorsum. The truck started and ran immediately when spraying ether into the throttle body, and died instantly when stopped spraying. In that location is NO fuel force per unit area at the schrater valve on the fuel rails. The fuel line was dry when I unhooked information technology from the filter. What am I missing? My next thought was to investigate the F to R tank switch in the cab. Could this accept gone bad and is no longer sending 12V to the pumps? Your assist would be greatly appreciated.

Post by **Steve83** » Fri Oct 02, 2009 12:42 pm

First, do the mod described in this caption & the Next few:

Information technology will eliminate the relays as a possible cause. If the FP relay stays ON whenever the key is in RUN (even when the engine isn't spinning), and then you probably have a bad EEC. I've seen a lot of threads almost '87-91 EECs dying lately.

But none of that will crusade the fuel line to be empty when the pumps are running. For that, click my black Bronco in my signature & read the captions in the '84-89 Fuel Reservoirs album.

Mail by **bimmerboy12** » Fri Oct 02, 2009 1:09 pm

Thank you for the help. Something to add; when I plough the primal to ON, the relay will immediately click...(intermission)...click. Turn information technology off, and you hear/feel nothing.

Sabbatum Oct 03, 2009 seven:08 am

That'south normal. When the EEC comes on, it primes the fuel pump. When information technology shuts off, obviously, it does nothing.

Post past **bimmerboy12** » Mon October 05, 2009 ii:53 pm

OK quick update: remember I said the voltage measured at the inertia switch at 6.9V? Well I tested the voltage for the MAIN IN to the fuel pump relay (thick orange wire) and it tested at half-dozen.9V. I jumped 12V to the relay (tapped into orange wire) and voila, the truck started correct up and ran like a summit. What would reduce the voltage to the relay down to 6.9V??? Something in the estimator?

Post by **Steve83** » Mon Oct 05, 2009 nine:46 pm

No. Something in the pump power excursion, which includes the tank select switch, the FP relay, a fusible link wire, & the EEC PWR relay.

Post past **bimmerboy12** » Tue Oct 06, 2009 6:22 am

I replaced the FP relay and I am checking the tank select switch tonight. I can go ahead a supersede the EEC relay as well. Where is the fusible link?

Post by **Steve83** » Tue Oct 06, 2009 8:21 am

Information technology doesn't matter what you replaced unless you tested it AFTERward, and it tests good. New parts can be bad. Y'all always have to check, and you SHOULD bank check before. If it tests proficient, leave information technology alone.

I was mistaken - the EEC PWR relay wouldn't create low voltage on the FP circuit.

The fusible link wire is somewhere between the Y wire on the FP relay & the starter relay. Information technology could be anywhere, but simply testing voltage at the Y wire at the FP relay while the pump is running will tell you if it'southward a problem.

Post by **tarosean** » Tue Oct 06, 2009 iv:35 pm

Steve83 wrote:That'south normal. When the EEC comes on, it primes the fuel pump. When it shuts off, plain, it does cypher.

So the EEC controls the fuel pump???

I am having a similar problem with a 93 F150 5.0/Auto..(single rear tank)

Although mine will not run for more than a min or two.
It seems like my fuel pump is priming nigh 1 in 20 attempts at starting, although information technology will non stay engaged. wiring/relays/Inertia switch are all good.

Pulled the EEC out, replugged it back up and the truck fired up for a min.

Post by **Steve83** » Tue October 06, 2009 10:00 pm

Not directly - it controls the FP relay. But all those other things are in that circuit, also, and any of them can close the pump down. Get a Haynes manual & study the wiring diagrams.

It'due south possible for the FP to run, simply not generate enough pressure for the engine to run. Get a estimate & attach information technology to the exam port on the fuel rail.

Post by **bimmerboy12** » Wed Oct 07, 2009 4:29 pm

OK heres the latest: I have adamant that at that place is a steady half-dozen.9V going into the fuel pump relay. I bought a haynes manual and studied the wire diagram. The only thing that is upstream from the relay is a fusible link and constant power. My problem is in that surface area. Where is the fusible link/power connexion for the fuel pump circuit? I know this is my issue because when i jump 12V to the thick xanthous wire (power in) for the FP relay, information technology starts right upward. The tank switch/inertia switch etc. are all downstream and aren't part of the problem. The book doesn't say anything most fusible link location.

Post past **Steve83** » Wed Oct 07, 2009 8:39 pm

It's probably at the starter relay, but I've seen them embedded in the harness. If you can't find it, pull a new power wire (overlay) from an unused position in the fuse cake to the FP relay. Install a 5A fuse; if it blows, try a vii.5A, then a 10A. If the pumps pull more than 15A, in that location's a problem.

Post by **bimmerboy12** » Thu Oct 08, 2009 5:24 am

That's kind of the direction I was leaning, except I was thinking peradventure an inline fuse and run power over from the starter relay. I tried tracing the yellowish wire, but it disappears into the primary harness. I establish 3 thick yellow wires coming out of my starter relay, so I tested each of those.... 12V running through all of them. Then either none of those are the source or the problem is between where I tested and the FP relay. I have half a mind to just trace the wire and find out exactly what the hell is going on... more out of curiosity than trying to gear up it!

Post past **Steve83** » Thu Oct 08, 2009 7:33 am

That's certainly an choice, but it's a lot of piece of work to open the harness, and even MORE closing it dorsum up if you lot plan to continue using it.

Post past **bimmerboy12** » Wed Jan 19, 2011 nine:31 am

I felt I had to close the loop on this trouble... the fusible link was going bad and only a couple strands of copper remained. This explains the reduced voltage running to the pump. I removed and put in a connector and it is completely fixed.