yo Mike,
Welcome!
Assuming no fuel leaks;
seems similar to what I have seen in other 92-96 Broncos and Ford trucks w/single tank.
The in-tank fuel pump assembly has a discharge check valve (to maintain system pressure during shutdowns and to minimize starting problems), an inlet screen for protection and fuel return provision.
The Supply Check Valve, which is normally closed, opens when the outlet pressure from the energized pump exceeds the opposing check valve spring force. When the pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply line pressure.
Note: Maximum fuel pressure is obtainable at WOT or the vacuum hose removed from the fuel pressure regulator.
If fuel lines/systems have been drained or evacuated, it may take up to 15 seconds to obtain the pressure specified.
I believe the PUMP's check valve is Stuck in open (full flow) state and allowing fuel to return to tank, thus reducing fuel pressure while engine is off.
I have a slightly similar issue when first starting in morning or after long shut-down; engine will crank over normally, but not run or run rough at low RPMs until it runs or shuts down. If I hear it stumbling, I shut it off, then turn key to start; it will fire up immediately.
I may try a Ford type fuel cleaner soon.
This is by Ryan M, a Ford Fuel Injector specialist; "After attaching the fuel pressure tester, run the fuel pump for 10 seconds. Check that the pressure is within specs, and it doesn’t leak down more than 5PSI within 60 seconds after pump shutdown."
From FORD EVTM
The electric fuel delivery systems differ in design and arrangement depending upon the vehicle and model year. To clarify understanding and to simplify diagnostic instruction, they are classified as either Type 1 (Single Tank) or Type 2 (Dual Tank):
Type 1: Single Fuel Delivery Assembly or In-Tank Fuel Pump Assembly *** (as in our Broncos) ***
Type 2: Dual Fuel Delivery Assembly (one assembly per tank)
FDS2 FUEL PRESSURE TEST
WARNING: BEFORE SERVICING OR REPLACING ANY COMPONENTS IN THE FUEL SYSTEM, REDUCE THE POSSIBILITY OF INJURY OR FIRE, AS OUTLINED UNDER "NOTES, CAUTIONS AND WARNINGS."
Key off.
Before releasing fuel system pressure at the Schrader fitting, observe the Warning Instructions to avoid fuel spillage and injury.
Install the fuel pressure tester.
Ground the fuel pump lead of the Data Link Connector (DLC) (see attachment) with a jumper at the FP lead.
Key On, Engine Off, to operate the fuel pump(s).
Verify that the observed fuel pressure is within specified limits for the engine being checked.
Specification: Fuel System Pressure (Key On, Engine Off) Refer to "Fuel Pressure Specification Table." (SEE PSIs Below)
Is fuel pressure within specification?
Yes GO to FDS3.
NO:
If low: GO to FDS10.
If high: GO to FDS11
FDS3 CHECK FUEL PRESSURE LEAKDOWN
Observe the "Notes, Cautions and Warnings" to avoid fuel spillage and injury.
Connect the Fuel Pressure Test Kit at the fuel pressure test point.
Connect a jumper to the FP lead of the DLC.
Key on, engine off.
Ground the test lead using the jumper wire to run the fuel pump.
Run the fuel pump for 30 seconds minimum.
Remove the test lead ground and note fuel pressure on the gauge.
Verify whether the fuel pressure remains within the specified 5 psi for 1 minute after the test lead is ungrounded.
On dual tank system, perform test for both tanks.
Does fuel pressure remain within 5 psi for 1 minute after the test lead is ungrounded?
Yes GO to FDS5.
No GO to FDS4.
FDS4 CHECK PRESSURE REGULATOR DIAPHRAGM CONDITION
(miesk5 Note, pull vacuum line off FPR, any gas aroma or gas, replace the FPR)
Key off.
Connect Fuel Pressure Test Kit at Schrader fitting on rail. Observe Warning Instructions to avoid fuel spillage and injury.
Start engine and run for 10 seconds.
Stop engine and wait 10 seconds.
Start engine and run for 10 seconds.
Stop engine and remove vacuum hose from pressure regulator.
Examine vacuum port in the pressure regulator for evidence of fuel leakage through the diaphragm.
Is vacuum port free of any fuel?
Yes GO to Group 10 of the Service Manual for leak test.
No REPLACE pressure regulator and RERUN test FDS2
FDS5 CHECK FUEL PRESSURE WITH ENGINE LOAD
Fuel pressure test kit installed.
Disconnect vacuum hose at the fuel pressure regulator and plug it.
Observe fuel pressure while driving vehicle with heavy accelerations.
Does fuel pressure reading remain within ± 3 psi during the test?
Yes UNPLUG vacuum hose and connect it to fuel pressure regulator. GO to FDS6.
No GO to FDS8
FDS6 CHECK FUEL PRESSURE REGULATOR
Fuel pressure test kit installed.
Install vacuum gauge to intake manifold.
Start engine and observe both gauge readings.
Accelerate the engine speed to lower the vacuum gauge reading.
Does fuel pressure gauge reading increase as the vacuum gauge reading decreases, and/or does fuel pressure gauge reading decrease as vacuum gauge reading increases?
Yes REMOVE vacuum gauge and fuel pressure test kit. GO to Section 2A for other possible causes.
NO GO to FDS7
FDS7 CHECK VACUUM SUPPLY
Key off.
Vacuum hose removed from the fuel pressure regulator and plugged.
Install a hand operated vacuum pump to the fuel pressure regulator.
Start engine.
Observe fuel pressure while applying vacuum.
Does fuel pressure reading change as the vacuum changes?
Yes SERVICE vacuum system. REMOVE plug from vacuum hose and RECONNECT to fuel pressure regulator.
No REPLACE fuel pressure regulator
FDS8 CHECK FUEL FILTER
Observe Warning Instructions to avoid fuel spillage and injury.
Key Off.
Install a second fuel pressure tester on Schrader valve equivalent installed between fuel pump and the in-line fuel filter, as close to fuel pump as possible.
Operate fuel pump as in FDS2 and compare pressure observed at fuel rail with the pressure observed at the fuel pump.
**** Is pressure at fuel pump within 5 psi of fuel rail pressure? ****
Note: When fuel pump is not in operation, the fuel delivery system is at the same pressure, regardless of location of pressure tap. Therefore, both gauges should read the same pressure when pump is not in operation. Any difference in pressure readings when fuel pump is not in operation is pressure gauge error.
Yes GO to Group 10 of the Service Manual for additional Description, Diagnosis and Testing.
No REPLACE in-line fuel filter and RECHECK pressure as in FDS2. If pressure is OK, GO to FDS3. If pressure is not OK, RECHECK fuel lines for kinks or other restrictions. SERVICE and RECHECK as in Step FDS2.
FDS9 CHECK VOLTAGE AT (BOTH for F series w/2 tnaks) PUMP SPEEDS
Key off.
Connect DVOM between Inertia Fuel Shut-off (IFS) and chassis ground.
Start and run engine.
Read voltage at idle and at 3500 rpm.
Is the voltage near 9 volts at idle and near 13 volts at 3500 rpm?
Yes CHECK fuel pump ground connection and service. If OK, REPLACE fuel pump.
No CHECK CCRM/VCRM for proper operation. CHECK fuses of the fuel pump circuits high and low. RERUN FDS2.
FDS10 CHECK REGULATOR FOR LOW PRESSURE CAUSES
Key off.
Remove return fuel line at fuel rail and connect short hose from rail to measured container of at least one quart capacity.
Ground FP lead as in step FDS2.
Key on, engine off.
Record fuel pressure and note whether fuel is being returned to measured container. Unground FP lead after 10 seconds or if container is more than half full.
Is fuel being returned while pressure is still low?
Yes REPLACE fuel pressure regulator and GO to FDS2.
No For type 2: CHECK both pumps. If both are low, CHECK voltage at both pumps before replacing pumps.
All others: REPLACE fuel pump assembly. GO to FDS2.
Note: When replacing fuel pump, clean out tank and replace fuel filter.
FDS11 CHECK REGULATOR FOR HIGH PRESSURE CAUSES
Key off.
Remove return fuel line at fuel rail and connect short hose from rail to measured container of at least one quart capacity.
Ground FP lead as in step FDS2.
Key on, engine off.
Record fuel pressure and note whether fuel is being returned to measured container. Unground FP lead after 10 seconds or if container is more than half full.
Is fuel pressure within specification?
Yes For type 2: GO to FDS12.
All others: GO to FDS13.
No REPLACE fuel pressure regulator and GO to FDS2.
FDS12 CHECK FUEL RETURN SYSTEM
Observe the "Notes, Cautions and Warnings" to avoid fuel spillage and injury.
Check the fuel return system(s) for restriction due to blockage, kinking, or pinching.
Remove the fuel return line at the fuel pressure regulator.
Apply 3-5 psi regulated shop air to the fuel return line.
Do you hear air entering either tank?
Yes REPLACE in-tank unit where air is entering. RECONNECT fuel return line.
GO to FDS2.
No GO to FDS13
FDS13 CHECK FUEL RETURN SYSTEM
Key off.
Observe the "Cautions and Warnings" to avoid fuel spillage and injury.
Fuel return line disconnected at the fuel pressure regulator.
Check the fuel return system(s) for restriction due to blockage, kinking, or pinching.
Disconnect the fuel return line near the fuel tank.
Apply 3-5 psi regulated shop air to the return line at the pressure regulator side.
On Type 2 system block return line at fuel tank on one tank and test through remaining line. Perform test for both tanks.
Does air flow freely through the line?
Yes For Type 2:
GO to Group 10 of the Service Manual for Description, Diagnosis and Testing of the FDM System.
For Type 1:
REPLACE fuel pump assembly. GO to FDS2.
No SERVICE the fuel return line. RECONNECT fuel line. GO to FDS2.
FDS14 CHECK FUEL INJECTOR FLOW AND LEAKAGE
Observe "Caution and Warning" to avoid fuel spillage and injury.
Verify that the fuel injectors flow within specification, using Rotunda Injector Tester 113-00001, SBDS Injector Flow Tester or equivalent.
Is flow rate for individual injectors within specification?
Yes CHECK fuel lines for leaks. GO to Group 10 of the Service Manual, then REPEAT Pinpoint Test Step FDS2.
No REPLACE the defective injectors as required. RERUN test FDS14. REPEAT FDS3.
FDS15 CHECK PUMP NOISE
Fuel Pump Noise on 3.0L Taurus Flex Fuel
Conditions that can produce noise are low Methanol fuel blends (less than 30%), high fuel volatility, low fuel level (quarter fill or less), and temperature greater than 75°F. Fuel system noise may become objectionable at start-up or at high engine speed if any of the conditions are present and are considered normal. The noise level can be reduced by taking corrective action. If the noise problem cannot be corrected following this procedure, refer to Group 10 of the Service Manual.
Key off.
Observe the "Cautions and Warnings" to avoid fuel spillage and injury.
Drain fuel tank to less than a quarter tank, then fill tank to at least half with M85 fuel (15% gasoline, 85% methanol).
Start engine and check for excessive fuel pump noise.
Was pump noise reduced by adding M85 fuel?
Yes ADVISE customer accordingly.
No GO to FDS16.
FDS16 CHECK PUMP SPEEDS
Key off.
Connect DVOM into Inertia Fuel Shutoff (IFS) switch connector.
Start engine and monitor voltage at the IFS.
Is voltage between 12 and 14 volts during crank and initial idle speed, then drops between 7 and 10 volts after a short time?
Yes GO to FDS17.
No Dual voltage system may be damaged. PERFORM Quick Test and repair DTC codes.
FDS17 CHECK PRESSURE DIFFERENCE
Key off.
Observe the "Cautions and Warnings" to avoid fuel spillage and injury.
Install fuel pressure test kit.
Install a second fuel pressure tester on Schrader valve equivalent between fuel pump and the in-line fuel filter, as close to the pump as possible.
Disconnect and plug vacuum hose from fuel pressure regulator.
Start engine and observe fuel pressure difference between gauges.
Key off, compare gauge readings within 10 seconds. Both should read the same, or else one gauge is in error.
Is fuel pressure difference between gauges less than 10 psi?
Yes REPLACE fuel pump assembly. INSPECT inside of tank for interference, contamination of fuel. SERVICE as necessary.
No REPLACE fuel filter. FILL tank with fresh fuel. REPLACE fuel filter and CHECK system per Group 10 of the Service Manual.
==========
PSI
Truck Engines:
ENGINE RUNNING
4.9L MFI 45-60 PSI
All Other Applications 28-45 PSI
KEY ON ENGINE OFF
4.9L MFI 50-60 PSI
All Other Applications 35-45 PSI
Note: Maximum fuel pressure is obtainable at WOT or the vacuum hose removed from the fuel pressure regulator.
If fuel lines/systems have been drained or evacuated, it may take up to 15 seconds to obtain the pressure specified.
Note: Grounding the FP lead at the DLC will allow the pump to run continuously with the ignition switch on.
The Supply Check Valve, which is normally closed, opens when the outlet pressure from the energized pump exceeds the opposing check valve spring force. When the pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply line pressure.
Fuel Pressure Regulator
The Fuel Pressure Regulator is attached to the fuel supply manifold assembly downstream of the fuel injectors. It regulates the fuel pressure supplied to the injectors. The regulator is a diaphragm-operated relief valve. One side of the diaphragm senses fuel pressure and the other side is connected to the intake manifold vacuum. Nominal fuel pressure is established by a spring preload applied to the diaphragm. Balancing one side of the diaphragm with manifold vacuum maintains a constant fuel pressure drop across the injectors. Fuel in excess of that used by the engine is bypassed through the regulator and returns to the fuel tank.
To rule out any others issues;
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
A helper is good to assist in reading Codes; best is to take a cell fone video and replay it.
Some basics;
Visual Check
1.Inspect the air cleaner and inlet ducting.
2.Check all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc.
3.Check EEC system wiring harness for proper connections, bent or broken pins, corrosion, loose wires, proper routing, etc.
4.Check the Powertrain Control Module (PCM), sensors and actuators for physical damage; IAC, TPS I see was replaced, etc.5.Check the engine coolant for proper level and mixture.
6.Check the transmission fluid level and quality. See E4OD Fluid Condition Check Below)
7.Make all necessary repairs before continuing
8. Check headlights
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it, if possible to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Turn off all accessories; radio, lights, A/C, heater, blower, fans, etc. (close driver's door)
Then turn off engine and wait 10 seconds.
Do KOEO test
Post Code(s) here according to:
KOEO
&
KOER, If it runs
Grounding the FP lead at the DATA LINK CONNECTOR (DLC) located under Driver side hood hinge will allow the pump to run continuously with the ignition switch on.
DLC is
and general info;
Fuel Pressure w/Key ON and engine Off should be 35—45; PSI but gauge may need calibration, if possible and/or a ambient & Under hood temperatures affects accuracy;
Engine running pressure should be 28—45 PSI
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."
