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Krafty

No Fuel Pressure Diagnostics

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This is a step by step guide on how to locate the source of your no fuel pressure problem on your fuel injected fords. some of the general testing information can also be applied to other non bronco and even non ford vehicles. This was a response to a no fuel pressure situation on an 89 bronco.

 

1- When you turn the Key to ON do you hear TWO PUMPS? (Note the Paragraph at the bottom about 87-91 vs 92 and up Fuel systems)

you need another set of hands so you can be under the gas tank to listen for the two pumps when the key is turned.

the Loud one is the high pressure pump on the frame rail under the drivers seat ( easy to hear) the second is the low pressure pump INSIDE the tank.

 

YES go to #2 NO go to #3

 

2- you can hear your pumps, but you still have little or no pressure on your fuel rail. Replace your fuel filter and your fuel pressure regulator on the fuel rail and check for pressure. turn the key on to run the pumps while the filter is off to flush out the fuel line,

 

Do you have pressure now?

Yes- it should run NO- you may have a dirty pickup in the tank ( rare).

 

3- If you dont hear both pumps then you need to do some testing, with a volt meter check for voltage at the pumps in the first 2 seconds after the key is turned on, check it a couple of times to ensure a consistent reading.

Do You Have Voltage at Both pumps but one or both are still not working?

 

Yes- #4 No - #5

 

4- if the pump or pumps are not working but there is voltage then replace the pump(s)

 

5- First check the inertia switch on the driver side, up aginst the fire wall to the left of the brake pedal or behind the right kick pedal.Push the reset button on the top of the switch to compete the circuit.

 

re check for voltage, if its a no then you need to test for power before and after the relay. no power before = no signal from eec, no power after = relay or relay plug.

 

I must clarify that only on the 87-91 efi vehicles (including F series and E series) these systems have the low pressure pump in the tank with the high pressure pump on the frame rail with the fuel reservoir with vapor recovery systems between the low pressure pump and high pressure pump, the fuel filter on these models is typically found after the high pressure pump just below the firewall. The 92-96 (and up)efi systems only use ONE pump which is a high pressure pump in the gas tank, the fuel filter is also on the frame rail but closer to the fuel tank. these vehicles have a vapor or excess fuel line that runs right back into the tank instead of having a fragile plastic reservoir on the frame rail.

 

adjust your diagnostics accordingly

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yo Krafty,

GOOD STUFF,

 

May I add this too?

 

Check Battery voltage - must be at least 12.4 volts.

Cranking voltage at the starter is at least 9.6 volts.

 

and to "3- If you dont hear both pump"

 

The Control Module (PCM) runs the pump(s) for one second when it receives an ignition-on signal. It also runs the pump(s) as long as it receives a PIP signal from the Hall-effect devices (inside the Distributor), 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.

 

"Check the fuel pump relay when cranking the engine over. Not the 2 second run after the key is turned on, but while cranking the engine. If the fuel pump relay kicks on when cranking, the TFI & Stator are good..."

Source: by Ryan M (Fireguy50) at oldfuelinjection.com

 

The pump(s) will also run when the terminals of the fuel pump test connector are jumped. the Control module signals the pump(s) when it receives a CRANK signal, and when the Control module gets PIP signals that the engine is running. the pump(s) do not run if the PIP indicates the engine is not running even with ignition ON {except for that first one second}.

 

In the Diagnostic Link Connectors for EEC-IV processors (84-95);

Connect Fuel Pump Test terminal to any ground (such as Signal Return) to force the fuel pump(s) on when the key is in RUN.

Diagram by my pal, BroncoJoe19

post-9476-1209780173_thumb.jpg

 

If pump(s) run, then diagnose the ignition ckt to the FP Relay.

Wiring Diagram in an 89 5.0, 5.8 & 7.5 (partial at FP relay); miesk5 Note; G801 is located on the LH inner fender behind the headlamp & both pumps Grounds join @ Splices S155 & S903

Source: by Seabronc (Rosie, Fred W) at http://broncozone.com/topic/20547-fuel-pump-wont-shut-off/

 

& Such as in; No Start Troubleshooting but Starter Cranks Engine in 4.9, 5.0, or 5.8L; "....TIP 1: Since a lot of folks confuse a No Crank Condition with a No Start Condition... I'll clear it up right now: In a No Start Condition means your vehicle's Starter Motor is cranking the Engine but the Engine is not starting. In a No Crank Condition, the Engine is not cranking when you turn the key to crank the Engine. This article only deals with a No Start Condition..." read more

Source: by easyautodiagnostics.com @ http://troubleshootmyvehicle.com/ford_no_start_4.9L_5.0L_5.8L/diagnose_no_start_1.php

 

Two electric pumps are used on fuel injected models to 1989; 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.

 

And it won't take much time to do a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test

 

Later, if you get it running; and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.

 

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

 

Do Key On Engine Off (KOEO) portion

 

Some typical DTCS are;

DTC 87 - FP relay circuit failure- suspect inertia switch, fusible link, FP relay

Source: by miesk5 at Ford Bronco Zone Forums

DTC 87, 95 & 96; "...These codes relate to low or no power reaching the fuel pump. Start testing at the fuel pump relay. The relay must respond to the EEC processor and the relay contacts must be a low resistance path for fuel pump power. Relay testing can be done in a couple minutes with the fuel pump test table. Fuel pump relay testing;1. Use solenoid test at EEC pin 22 to check relay coil current draw. 2. Voltage at pump power terminal must be within .5v of battery power when relay is turned on with amp meter at pin 22. Check power from battery if voltage is low. Check the inertia switch and fuse if battery voltage is missing. Pin 22- (light blue-orange) Grounded to turn "on". Voltage will drop to about 1v when "on". Current draw will be 160 to 270mA Pin 8- fuel pump monitor (dark green-yellow) 0v engine off, battery voltage with engine running..."

Source: by Dustin S (Dustball, Mellow Yellow, Mr. Laser Boy)

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Krafty and miesk5,

 

Great stuff!

 

I'd like to add, that the ground is the other half of the electrical circuit, and a poor ground may cause a pump to not pump, or a relay not to close.

Three important grounds are:

 

left upper radiator support

 

right upper radiator support

 

near the PCM/EEC - driver's side hood hinge

 

SO with that thought in mind, if you have power to the pump at the connector to the pump, and it doesn't run, try grounding the ground wire at the connector to the pump, if it still doesn't run, then pull the pump.

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