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66-96 Ford Broncos - Early & Full Size
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88 fuel gauge problem

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I just got an 88 and when you get in it with out the key on the gauge shows a fuel level but when you start it the fuel gauge goes to empty like it should when it off. Any suggestions on what to do? The guy I bought it from did say he put a new fuel pump in it. Which resides another problem. The fuel pump runs the whole time with the key in the on position.

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yo MRS.


Tech Tip Guide, General; "...Many times, the Ford fuel pump hanger/sender assemblies are frequently found with extensive corrosion on the cover and on the metal tubes. Over time, the terminals can loosen and cause intermittent loss of continuity. Erratic reading of the fuel sender level is one of the other problems that could occur..."
Source: by spectrapremium.com


Testing; "...the little resistive strip in them gets bad and causes erratic readings. Also, while you are at replacing it, check out the connector to make sure the ground is good back to the battery. Do a resistance check from the black lead to the battery (-) post. If is is more than a couple of ohms, run a new ground lead to it..."
Source: by Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums



Testing & Connector Pin-Outs ; for '92-96 Broncos ('87-96 F-series & Bronco similar)
 Sender Range: Full = 160 Ohms; Empty = 16 Ohms; "... gauge that pegs past full indicates an open circuit (broken wire; unplugged connector; corroded terminal; burned sender) on the Y/W wire. gauge that pegs past empty indicates a short to ground (pinched to the frame, body, or dash supports) on the Y/W wire, OR a sunk float. gauge anywhere in between that doesn't move indicates an open circuit (blown fuse; corroded terminal) on the power (battery) side of the gauge OR a bad instrument cluster ground at C251 pin 9. The terminals of C251 (& C250) are known to corrode & lose contact. Polish both the connector pins AND the film circuit pads with brown paper or a pink eraser. The larger version of C441(WPT454) was used until 93. The level sender can usually be disassembled & repaired by bending the wiper arm inside the plastic housing to apply slightly more force..."

Source: by Steve  http://www.supermotors.net/registry/media/744437


Testing in 87-88 Bronco & F Series; When the fuel gauge needle is below the 1/2 to 1/4 tank range the needle will swing all the way above the full mark on the fuel gauge; An erratic fuel gauge needle when the fuel tank is 1/2 to 1/4 full may be caused by excessive wear of the resistive film on the fuel pump sender assembly. The wear occurs during transporting of the vehicles via rail or truck over long distances. The fuel gauge will indicate correctly from a full tank to about 1/2 or 1/4 tank of fuel. When the fuel gauge needle is below the 1/2 to 1/4 tank range the needle will swing all the way above the full mark on the fuel gauge. To correct this, install a new fuel pump sender assembly. Refer to the appropriate 1988 Car/Light Truck Shop Manual, Section 24 for detailed service information. Refer to the following fuel pump sender application chart for the correct service part number. in Fuel Gauge Erratic TSB 88-18-03 87-88 Bronco & F Series 4.9L/5.0L (all PN E9VY-9275-A) & many others; Miesk5 Note, Steve83 wrote, Pre-'87 fuel level senders are TOTALLY different from '87-up. Not only do they work over a different range; they work in the opposite direction
Source: by Ford via Steve





Fuel Pump Circuit Operation

When the ignition is switched to the ON position, it turns the EEC Power Relay on. The EEC Power Relay provides power to the EEC-IV processor and the control side of the fuel pump relay. Power for the fuel pump is supplied through a fuse link or high current fuse attached to the starter solenoid (battery side). From the fuse link or high current fuse, current flow is through the fuel pump relay and Inertia Fuel Shutoff (IFS) switch to the fuel pump. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. If the IFS switch is "tripped," it must be reset by depressing the white or red button on the top of the switch. The fuel pump relay is controlled by the Powertrain Control Module (PCM).

When the ignition switch is turned to the ON position, the fuel pump will operate. If the ignition switch is not turned to the START position, the PCM will shut the fuel pump off after approximately one second. The PCM will operate the fuel pump when the ignition is in the START position to provide fuel while cranking.

After the engine starts, the PCM will continue to operate the fuel pump unless the engine stops, engine speed drops below 120 rpm, or the IFS switch is "tripped."


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..." 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}. 
Source: by Steve at

READ MORE http://www.supermotors.net/registry/media/245234


Test Fuel Pump Relay



[/url] Connect FP Relay (terminal A) to any ground (like terminal E) to force the fuel pump(s) on when the key is in RUN. dlcjumper.jpg . eecconnectors.jpg Pins D & F are a primitive SCP bus, but on these old vehicles, nothing else was networked in. Connect pin 1 (209 W/Pu) to any ground (like terminal E) with any jumper wire (like a paperclip) to trigger diagnostic modes. (See the NEXT diagram.) Consult the 7th post on this page for the compete procedure to pull codes & trigger all test modes. If the CEL is burned out, connect CEL © to a 12V test light, and the light's other terminal to a 12V source on the same vehicle. To hardwire a self-test switch in the dash, see: selftestswitch.jpg Diagnostic Link Connectors for EEC-IV processors ('84-95).
'84-86 (red) located on R wheelwell near starter relay.
'87-95 (black or gray) located under L hood hinge under EEC TEST cover. (WPT-743 & WPT-352)
'94-96 Bronco - do not confuse with RED 4WABS connector also under L hood hinge

87-89; Fuel Injected Engines - "...Two electric pumps are used on fuel injected models; a low pressure boost pump mounted in the fuel tank and a high pressure pump mounted on the vehicle frame. The low pressure pump is used to provide pressurized fuel to the inlet of the high pressure pump and helps prevent noise and heating problems. The externally mounted high pressure pump is capable of supplying 15.9 gallons of fuel an hour. System pressure is controlled by a pressure regulator mounted on the engine..."


 Will post for now; Comcast is so slow that my PC will freeze, again

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