Mechanics

F150 FUEL PUMP PROBLEMS

1990 Ford F-150

Electrical problem
1990 Ford F150 V8 Two Wheel Drive 90000 miles

I was driving and my engine just quit. I poured fuel in the intake and it runs for a short time. The fuel pump doesnt come on with key. I have twin tanks and neither works so I ruled out the fuel pumps. I got a wireing diagram and checked the Relay Inertia switch and the tank switch and they all had 6.5 volts. Shouldnt it be 12v? I think maybe the fused link could be half blown. Does this sound logical and if so where is it?
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Wayne trammell
June 20, 2009.




FUEL DELIVERY (PICKUP & F-SUPERDUTY) In-Tank Reservoir (ITR) Fuel Pump Testing 1. Ensure fuel tank has adequate fuel. Turn ignition off. Install fuel pressure gauge. Install a test lead to Fuel Pump (FP) lead of VIP test connector. See Fig. 9 . Turn ignition on, engine off. Ground test lead to run fuel pump. Check fuel pressure. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification, go to step 5). If fuel pressure is not within specification, go to next step. 2. If pressure is low, but greater than 3 PSI (21 kPa), go to next step. If pressure is not more than 3 PSI (21 kPa) go to step 4). 3. Check fuel system for: Plugged fuel filter (replace filter and check again for proper pressure). Kinked/restricted fuel lines (visual inspection). Low voltage to fuel pump (should be within 0.5 volt of battery voltage at connector). Disconnect return fuel line and note if fuel is being returned during this low pressure condition. If fuel is being returned, replace or adjust pressure regulator. If a problem was found, repair as necessary. After repair, go to step 1) and retest system. If a problem was not found, replace fuel pump and go to step 1) and retest system. 4. Check the following electrical circuit problems: Ensure inertia switch is not open (reset switch as required). Wiring at fuel pump/tank connector loose or open. Fuel pump ground connection at chassis loose or defective. Improper fuel pump relay operation (should operate when fuel pump test lead is grounded with the ignition key on). EEC relay not operating if fuel pump relay doesn't operate. If a problem was found, repair as necessary. After repair, go to step 1) and retest system. If a problem was not found, replace fuel pump and go to step 1) and retest system. 5. Remove ground from test lead and note pressure on gauge. Pressure should remain within 2 PSI (14 kPa) for 3 minutes after lead is ungrounded. If pressure holds as specified, go to step 7). If pressure does not hold as specified, go to next step. 6. Check fuel lines and connectors for leakage. Disconnect fuel return line and plug engine side. Momentarily activate fuel pump by grounding test lead. Raise pressure to approximate operating pressure and repeat step 5). If pressure holds, replace pressure regulator and repeat step 5). If pressure decays rapidly, go to next step. If system still fails step 5), there may be a leaking fuel injector or rail. Repair as necessary and go to step 5). 7. If pressure decays rapidly enough that needle movement can be observed, replace ITR unit if equipped with a single tank. If equipped with dual tanks, go to next step. If pressure holds, go to step 10). 8. Remove fuel supply line from sender port of midship tank. Change pressure gauge from 5/16" to 3/8" adaptor to fit fuel line quick connector. Connect gauge to end of supply line removed frommidship sender. Move the tank selector switch to REAR tank position. Turn ignition on and hold until fuel pump shuts itself off (approximately one second). Turn ignition off. Observe pressure gauge. If pressure holds steady, go to next step. If pressure does not hold steady, replace rear ITR unit and go to next step. 9. Remove fuel pressure gauge from supply line. Install a 3/8" right-angle quick-connector to pressure gauge. Connect gauge to midship tank ITR supply port. Move the tank selector switch to the FRONT tank position. Turn ignition to on position and hold until fuel pump shuts itself off (approximately one second). Turn ignition off. Observe pressure gauge. If pressure holds steady, midship ITR unit is okay. Remove fuel pressure gauge and reconnect all fuel lines. Go to step 1) to retest system. If pressure does not hold steady, replace midship ITR unit. Go to step 1 to retest system. 10. Disconnect and plug vacuum line connected to the pressure regulator. Start engine and run at idle. Check fuel pressure. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification, go to step 12). If fuel pressure is not within specification, go to next step. 11. Check the following for cause of low pressure: Fuel filter restriction. Improper fuel regulator adjustment. Fuel line restricted. Improper voltage to fuel pump (battery voltage at pump connections). If a problem was found, repair as necessary. After repair, go to step 1) and retest system. If a problem was not found, replace fuel pump and go to step 1) and retest system. 12. With engine running at idle and vacuum line disconnected, note fuel rail pressure. Rapidly accelerate engine and watch fuel pressure. If pressure remains within 5 PSI of starting pressure, system is okay. If pressure does not remain within 5 PSI of starting pressure, go to step 11). NOTE: Road testing vehicle while monitoring pressure may give a better test under load conditions.


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Merlin2021
Jun 20, 2009.
This answer sucks. Why do I cear about fuel pressure tests when I dont have eather fuel pump working. I only have 6.5 volts at the relay.

Tiny
Wayne trammell
Jun 20, 2009.
Did you see the part about grounding the fuel pump TEST connector? Yes 6 volts is low, did you bother to read my reply? It tells you voltage should be within.05 volt of battery voltage, now ground the test connector and see if the d_a_m_n thing runs.

Merlin2021
Jun 20, 2009.
Wayne do this test, and get back to me, we will get it going, but testing IS needed, I am not at your truck so these tests are helpful, with only 6.5 volts, the ground is either corroded or broken. Pull the connector aprat and look for corrosion(green goo) and clean it with brakkleen or electrical contact cleaner. If none found, check continuity of the ground wire.
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Merlin2021
Jun 20, 2009.

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