Seabronc
New member
Have you had a hard bump lately? Could be the inertial switch, they have been known to go bad and sometimes pop without any apparent reason.
90 Bronco wiring help
- Thread starter AHBronco90
- Start date
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AHBronco90
New member
That's the first thing I checked seabronc. It looks good and pressed it. I checked the fuel pressure by pressing that pressure checker( not sure of the name lol looks like the place you put air in a tire, and no fuel came out. I followed the fuel pump wiring and had some questions. There's a harness disconnected near the back of the truck coming out near the bottom of where the driver seat is.( I'll post a pic) nothing plugged into it. I changed the fuel pump relay and nothing new.
I did plug in an unplugged harness near the fuel pump relay and got fuel pressure, fuel came out! But it didn't happen again. I'm not sure what the plug is but it has 4 pins and circular with two bigger wires (red,yellow) and 2 smaller ones (blackw/white stripe and brown. Its plugged into a harness with matching wires but I plugged it into another one that's unplugged with four wires ( different colors, orange, red/w gray, blue, and brown w/white strip) that's the plug I plugged in when there seemed to be fuel pressure. ( not sure if its related lol but something happened lol)
Sorry, I know this is a lot and unclear due to my lack of knowledge but if anyone has advice on where I should go next that'd be great!
Harnesses by the fuel pump relay
harness unplugged coming from under driver seat
wiring from fuel pump
I did plug in an unplugged harness near the fuel pump relay and got fuel pressure, fuel came out! But it didn't happen again. I'm not sure what the plug is but it has 4 pins and circular with two bigger wires (red,yellow) and 2 smaller ones (blackw/white stripe and brown. Its plugged into a harness with matching wires but I plugged it into another one that's unplugged with four wires ( different colors, orange, red/w gray, blue, and brown w/white strip) that's the plug I plugged in when there seemed to be fuel pressure. ( not sure if its related lol but something happened lol)
Sorry, I know this is a lot and unclear due to my lack of knowledge but if anyone has advice on where I should go next that'd be great!
Harnesses by the fuel pump relay harness unplugged coming from under driver seat wiring from fuel pump
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AHBronco90
New member
Guys I its good to go!!!! I can't thank all of you enough. I learned a lot through this and I'm grateful you guys passed on your knowledge! The 351 sounds like a beast and probably woke up half my neighborhood lol
Seabronc
New member
AHBronco90
New member
I switched the new computer out for the original one and replaced the fuel pump relay. When I put the ignition switch in the on position I heard the hum of the fuel pump so I put it in start and it fired up right away!
Last edited by a moderator:
Seabronc
New member
Thanks for the feedback 
/
Good luck,
>-
/Good luck,
>-
Yo ah,
Operational Sequence;
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. 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}
EEC relay energizes the fuel pump relay---so, if it's bad then the pump won't run. Pull both etc and fp relays, inspect sockets for corrosion, bad wiring...
http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=17290
90 Bronco 5.8 fuel control system wiring diagram
Inertia Fuel Shutoff (IFS) Switch
The IFS switch is used in conjunction with an electric fuel pump. The purpose of the IFS switch is to shut off the fuel pump in the event of an accident. It consists of a steel ball held in place by a magnet. When a sharp impact occurs, the ball breaks loose from the magnet, rolls up a conical ramp and strikes a target plate which opens the electrical contacts of the switch and shuts off the electric fuel pump. Once the switch is open, then it must be manually reset before restarting the vehicle.
http://broncozone.com/uploads/monthly_04_2012/post-3816-0-10233600-1334748190.gif
Figure 4: Inertia Fuel Shutoff (IFS) Switch
Reset Instructions
Turn ignition to OFF.
Check for leaking fuel in the engine compartment, fuel lines and tank(s).
If no fuel leak is apparent, reset the IFS switch by pushing the reset button on the top of the switch (refer to Owner Guide).
inertiaswitchopencloseddepiction.jpg
Note in the closed position the button can be depressed on additional 1/16 inch against a spring.
Turn ignition switch to START for a few seconds, then to OFF.
Again, check for leaking fuel.
Btw, our friend Bronco Joe wrote, "In my '90 the inertia switch is by the driver's left foot on the firewall."
as Steve shows in this Fuel Pump Test & Diagram at the Diagnostic Link Connector in 84-95;
"...Connect FP Relay to any ground to force the fuel pump(s) on when the key is in RUN..."
Operational Sequence;
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. 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}
EEC relay energizes the fuel pump relay---so, if it's bad then the pump won't run. Pull both etc and fp relays, inspect sockets for corrosion, bad wiring...
http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=17290
90 Bronco 5.8 fuel control system wiring diagram
Inertia Fuel Shutoff (IFS) Switch
The IFS switch is used in conjunction with an electric fuel pump. The purpose of the IFS switch is to shut off the fuel pump in the event of an accident. It consists of a steel ball held in place by a magnet. When a sharp impact occurs, the ball breaks loose from the magnet, rolls up a conical ramp and strikes a target plate which opens the electrical contacts of the switch and shuts off the electric fuel pump. Once the switch is open, then it must be manually reset before restarting the vehicle.
http://broncozone.com/uploads/monthly_04_2012/post-3816-0-10233600-1334748190.gif
Figure 4: Inertia Fuel Shutoff (IFS) Switch
Reset Instructions
Turn ignition to OFF.
Check for leaking fuel in the engine compartment, fuel lines and tank(s).
If no fuel leak is apparent, reset the IFS switch by pushing the reset button on the top of the switch (refer to Owner Guide).
inertiaswitchopencloseddepiction.jpg
Note in the closed position the button can be depressed on additional 1/16 inch against a spring.
Turn ignition switch to START for a few seconds, then to OFF.
Again, check for leaking fuel.
Btw, our friend Bronco Joe wrote, "In my '90 the inertia switch is by the driver's left foot on the firewall."
as Steve shows in this Fuel Pump Test & Diagram at the Diagnostic Link Connector in 84-95;
"...Connect FP Relay to any ground to force the fuel pump(s) on when the key is in RUN..."
