'91 Bronco Fuel Pump Issues

I've been replacing different parts of my engine as they've needed replacing, trying to keep ahead of them as to keep it on the road. 

This week though, I got a fun new surprise - the fuel pump is not working. 

From what I've been reading, the '90 had two pumps, one in-tank and one in-line, but the '91 only has the in-tank ---Is that correct?

I have a '91, with a 5.8, just to clarify. It wasn't the original engine, but it's what I got, so there are wires in the engine compartment that don't exactly have a purpose. 

My other question is, through my reading, I've heard that the fuel pump relay and the fuel pump inertia switch can also go out, leaving you with a non-responsive pump. Are these both in my '91? And if so, should I check them first?

I've been doing most of my repairs in my apartment parking lot, but they don't seem to like that very much, so I may have to tow it somewhere to work on it. With the fuel tank currently having gas in it, is there any concern with doing it myself, other than being cautious, or should I seek professional assistance?

Thanks

John

My 1990 5.8 L only has one fuel pump, it is in the tank. Yes the inertia switch below the glove box behind the trim pannel and the fuel pump relay undder the hood drivers side...the one with the green plug can cause the fuel pump to not operate. all of the relays under the hood are all the same. What i mean is that they all function alike, therefoore they can be swapped. One is the fuel pump one is the EEC= Electronic Engine Control and on my truck the other one is for the trailer towing. The horn relay may also be there as well if not its under the dash i cant remember. Now the EEC relay can indirectly affect the fuelpump relay if it doesnt power up the Computer then the computer cant operate the fuelpump relay.

 So start at the beginning;

1 check fuses with a volt meter or atleast a test light, dont trust your eyes

2 check power the fuel pump relay.

3 check power to and from the inertia switch button on top of switch should be pushed down.

4 check power AT the connector to the fuel pump. this can be difficult since the pump connector is on TOP of the fuel tank. If you have a body lift on the truck its no problem otherwise follow the wires along the frame and toward the pump as far as you can and check for 12V. A volt meter is best for this since the test light will light up with less than 12 v but the pump will not operate with less than 12v.

Dropping the tank is a bit of a job if it has been a long time since it was done last. the bolts tend to get dirt caked up on them and a bit of rust added tto the mix can make them hard (not impossible) to get out. Then you have to deal with the weight of the fuel in the tank and at about 8 pounds a gallon with it sloshing around in the tank this job gets fun quickly. I have done many like this on my back and by myself. Its not reccomended as a one person job. Your other option is to cut a hole in the floor just above the fuelpumps location. This is the plan i followed and it put the hole perfectly over the fule pump. http://broncozone.com/forums/index.php?showtopic=12329

yo John,

As Elmo advised;

to help w/ wiring

Relay Wiring Diagram in a 90
Source: by Seattle FSB (SeattleFSB)

http://www.supermotors.net/registry/media/854315

Location pic; GREEN Connector pic, next to the Brown Connector Under hood behind air cleaner assy; pic in a 90 & up to 91
Source: by Need4racin (The 90 Bronco, Dean) at http://web.archive.org/web/20130922133127/http://img130.imageshack.us/img130/9307/temp90pics033ru4.jpg

Test & Diagram at the Diagnostic Link Connector in 84-95; "Connect Diagnostic Link Connector (terminal A) to any ground (like terminal E) to force the fuel pump on when the key is in RUN..."

Source: by Steve at http://www.supermotors.net/registry/media/245234



MIESK5 NOTE; Steve made an error and substituted FP Relay for Diagnostic Link Connector (terminal A) in his narrative

from Ford EVTM; The Control Module (PCM) runs the pump{s} for one second when it receives an ignition- on signal. It also runs the pump as long as it receives a PIP signal from the Hall-effect devices, it continues pump operation even after the key is released from START. If the PIP signals fall below 120RPM, the control module cuts off the signal to the fuel pump relay or the integrated relay control module. The pump will also run when the terminals of the fuel pump test connector are jumped. the Control module signals the pump when it receives a CRANK signal, and when the Control module gets PIP signals that the engine is running. the pump does not run if the PIP indicates the engine is not running even with ignition ON {except for that first one second}.

More testing
 

yo John,

I had to get some chow...

Inertia Fuel Cut-Off Switch

"Inertia Switches, The old switch (84~89) was installed on the firewall either just forward of the brake or clutch pedal or just R of the transmission tunnel. The later switch (~90-up) is always inside the R kick panel just below the glove box."


Source: by Steve

Okay Gents, I appreciate it - I'll get on this pronto. Thanks. 

Im having this problem with my 88 2.9. I just found a ground wire from my battery to my relays has a connector clip heavily wrapped in tape. I pulled the tape off and sure enough, the clip is EXTREMELY corroded. I am bypassing this oval shaped connector and Ill let you know if it worked once my battery is fully charged.

The weird thing is all my relays read hot when they were supposed to, so I though a ground up there wouldnt be an issue.. then I thought of my sub woofers, when they hit too hard with a bad ground, they cut out, die. 

I think this could apply to a fuel pump relay, getting it primed doesnt take much power, but actually running the fuel constantly during driving or actually firing up would cause a lot more pull on the relay, causing it to need a more solid ground. 

I do not know if this will fix it, but after 3 days of crawling around on the concrete it's worth a shot.

As for your inertia/ fuel pump shut off switch, my buttn was slightly raised. I whacked it with a crowbar and tripped it, reset it, nothing. So I pulled the plug out and inserted a paper clip to bypass the inertia switch in the event that that was the problem.

Ive done both of these with the battery out, so if it does fire up, I wont be certain which one fixed it.

A new development: I went out to check the relays, turned the key to start so the radio would play while I checked them, and I heard the fuel pump prime up, so I turned the ignition and it started right up.

Does this scenario isolate any one of those systems in particular?

YO J,

Did you touch the FP or EEC Power Relays?

If so, could have corrosion/loose sockets/wiring at the relays.

Next as a WAG,

When turning Ign Key to:

 start position, did starter crank as nomal, but fuel pump didn't run?

 or accessory position, did radio come on  when on button was pressed?

if not,  test the ign switch near strg column base

Switch Pin-Out Diagram & Continuity Testing (Logic Tables in 87-91 (from Factory Manual and the Ford Electrical & Vacuum Troubleshooting Manual (EVTM)
Source: by Broncobill78 (Dave) at http://broncozone.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=6659

Operational Sequence; "...The computer turns on the fuel pump relay 1. For about 1 second when you first turn the key to ON and 2. when it senses rotation in the dizzy from the pickup. You should test your relays by applying 12 V across the small terminals, listen for the click and check continuity across the large terminals. This will rule out the relays themselves being a problem. Usually they ARE the problem, so hopefully you can stop there. They absolutely HATE moisture so if you are missing your cover Im sure some moisture got inside the relays themselves. The pickup in the distributor can throw a code when it is intermittent or not working. One of many reasons you should check your codes..."

Source: by kf4amu

MIESK5 NOTE; from Ford EVTM; The Control Module (PCM) runs the pump{s} for one second when it receives an ignition- on signal. It also runs the pumps as long as it receives a PIP signal from the Hall-effect devices, it continues pump operation even after the key is released from START. If the PIP signals fall below 120RPM, the control module cuts off the signal to the fuel pump relay or the integrated relay control module. The pump will also run when the terminals of the fuel pump test connector are jumped. the Control module signals the pump when it receives a CRANK signal, and when the Control module gets PIP signals that the engine is running. the pump does not run if the PIP indicates the engine is not running even with ignition ON {except for that first one second}.
 

I didn't touch anything. Not a dam thing - that's what's so trippy about it. This thing boggles my mind sometimes. The truck has just been sitting there for four days. 

1) Before the malfunction ever happened, I could hear the fuel pump prime when I would turn the key to the start position, then once I turned the ignition it would start fine. 

2) When it stopped starting, I would turn the key to the start position and hear no priming at all. When I would turn the ignition, it would crank and crank, but wouldn't turn over. 

2b) It continued this way for the next 36 hours, as I continued to go out and try to get it to turn over by pumping the gas pedal and what not. 

3) Today, it fired up just like 1), and the radio and everything worked just fine. 

I know it's wasn;t the inertia switch, but could it now be the starter itself? Is it just not sending the right signals out - I'm sorry, but I'm terrible with the electrical systems. 

yo JPM,

I understand and will address non-electr. troubleshooting;

let us know if the FP and EEC Power relays react to what Ford describes as a "wiggle test"; shake or tap relays and wiring one at a time beginning w/FP relay while engine is running and see what happens w/pump. 

or when pump does not run after turning key to start, tap relays again  beginning w/FP relay and have helper turn key to start and see what happens.

Watch fan, belt pulleys, hot engine, etc.