Fuel Pump...dumb question

[LEB Ben]

Hey fellas...Dad just called a little bit ago, and said he wanted to take Thunder to take a load to the dump. He said all he can do is get it to turn over, and doesn't hear the fuel pump coming on when he turnes the key. Also said he wasn't getting any fuel to the fuel rail. He said the fuses checked out and said the reset wasn't tripped. So the dumb question I have is, where is the fuel pump on this thing...never had a problem, so I never looked. Is it in the top of the tank, or is it an inline along the frame? It's a dual tank rig, and the pump doesn't come on for either tank. So, can someone answer my dumb question, and is this in fact more than likely a fuel pump issue? Thanks in advance.

 

[1985 Ford F-150]

On my 85 its on the driver side frame rail.

 

[Truckin4life]

I have been told 2 things...
1 there are to feeder pumps in the tanks that feed into 1 high pressure pump on the frame rail....
2 each tank has its own high pressure pump....

I am partial to number two, but have yet to check my book...
If neither pump is comin on... I suspect an electrical problem, did he check the fuse box under the hood?

 

[m78]

There might be one common ground

 

[Truckin4life]

or a loose fuse... ?

 

[smokey]

Fuel pump relay

 

[Skandocious]

There are two high pressure pumps in that truck, 1 in each tank. If you don't hear either one of them priming when turning the key to ON then the problem is not at the lump. If the inertia switch wasn't tripped then Randy is most likely correct-- fuel pump relay. Under the hood.

 

[blackhat620]

Ben,

There are several things that need to be checked if the fuel system is not delivering fuel.

MULTI-PORT AND SEQUENTIAL FUEL INJECTION SYSTEMS

The fuel pressure regulator maintains a constant pressure drop across the injector nozzles. The regulator is referenced to intake manifold vacuum and is connected parallel to the fuel injectors and positioned on the far end of the fuel rail. Any excess fuel supplied by the pump passes through the regulator and is returned to the fuel tank via a return line.
The pressure regulator reduces fuel pressure to 39-40 psi (269-276 kPa) under normal operating conditions. At idle or high manifold vacuum condition, fuel pressure is reduced to approximately 30 psi (207 kPa).
The fuel pressure regulator is a diaphragm operated relief valve in which the inside of the diaphragm senses fuel pressure and the other side senses manifold vacuum. Normal fuel pressure is established by a spring preload applied to the diaphragm. Control of the fuel system is maintained through the EEC power relay and the EEC-IV or EEC-V control unit, although electrical power is routed through the fuel pump relay and an inertia switch. The fuel pump relay is normally located on a bracket somewhere above the Powertrain Control Module (PCM) and the inertia switch is located in the cab. The in-line fuel pump is usually mounted on a bracket at the fuel tank, or on a frame rail. Tank-mounted pumps can be either high or low-pressure, depending on the model.
The inertia switch opens the power circuit to the fuel pump in the event of a collision. Once tripped, the switch must be reset manually by pushing the reset button on the assembly. Check that the inertia switch is reset before diagnosing power supply problems to the fuel pump circuit.

Fuel Pump
The fuel delivery system uses either a high or low-pressure in-line or in-tank electric fuel pump, with some models equipped with both. It is a recirculating system that delivers fuel to a pressure regulating valve in the throttle body and returns excess fuel from the throttle body regulator back to the fuel tank. The electrical system uses two types of control relays, one controlled by a vacuum switch and the other controlled by the powertrain control module (PCM) to provide power to the fuel pump under various operating conditions.

An inertia switch is used as a safety device in the fuel system. The inertia switch is located in the cab, generally under the dashboard on the right side. It is designed to open the fuel pump power circuit in the event of a collision. The switch is reset by pushing each of 2 buttons on the switch simultaneously (some models use switches with only one reset button). The inertia switch should not be reset until the fuel system has been inspected for damage or leaks.
When the ignition switch is ON , it turns the EEC power relay ON . The EEC power relay provides power to the powertrain control module (PCM) and the control side of the fuel pump relay. Power for the fuel pump(s) 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 flows through the fuel pump relay and inertia switch to the fuel pump(s). The fuel pump relay is controlled by the PCM.
When the ignition switch is turned ON , the fuel pump(s) will operate. If the ignition switch is not turned to the START position the PCM will shut the fuel pump(s) OFF after 1 second. The PCM will operate the fuel pump(s) operate the fuel pump(s) when the ignition switch is turn to START position to provide fuel while cranking.
After the engine starts, the PCM will continue to operate the fuel pump(s) unless the engine stops, drops below 120 rpm or the inertia switch is tripped.

1987-89 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.


1990-1996 trucks use a high pressure pump which is part of the modular, In-Tank Reservoir (ITR) assembly. Besides the pump, the ITR consists of a venturi jet pump, a supply check valve and a shuttle selector valve. All this is mounted on the fuel gauge sender flange. The sending unit is separate from the ITR module.

CAUTION
Fuel supply lines on vehicles equipped with a high pressure fuel system will remain pressurized for long periods of time after engine shutdown. The fuel pressure must be relieved before servicing the fuel system.

Relieving Fuel System Pressure
A special tool is necessary for this procedure.
1. Make sure the ignition switch is in the OFF position.

2. Disconnect the battery ground.

3. Remove the fuel filler cap.

4. Using MFI Pressure Gauge T80L-9974-A, or equivalent, at the fuel pressure relief valve (located in the fuel line in the upper right corner of the engine compartment) relieve the fuel system pressure. A valve cap must first be removed to gain access to the pressure relief valve.


VOLUME TEST

1. Operate the engine at the specified idle rpm.

2. Open the hose restrictor and catch the fuel in the container while observing the time it takes to pump 1 pint. 1 pint should be pumped in 20 seconds. If the pump does not pump to specifications, check for proper fuel tank venting or a restriction in the fuel line leading from the fuel tank to the carburetor before replacing the fuel pump.

Go here and sign up then you can look at the repair manual for free
www.autozone.com/autozone/repairinfo/repairInfoLanding.jsp

 

[Truckin4life]

ah yes, under the hood drivers side fender...

 

[LEB Ben]

Fuel pump relay was swapped with a supposed good one...still the same thing...although doesn't mean the extra relay wasn't garbage too.

Ben,

There are several things that need to be checked if the fuel system is not delivering fuel.

MULTI-PORT AND SEQUENTIAL FUEL INJECTION SYSTEMS

The fuel pressure regulator maintains a constant pressure drop across the injector nozzles. The regulator is referenced to intake manifold vacuum and is connected parallel to the fuel injectors and positioned on the far end of the fuel rail. Any excess fuel supplied by the pump passes through the regulator and is returned to the fuel tank via a return line.
The pressure regulator reduces fuel pressure to 39-40 psi (269-276 kPa) under normal operating conditions. At idle or high manifold vacuum condition, fuel pressure is reduced to approximately 30 psi (207 kPa).
The fuel pressure regulator is a diaphragm operated relief valve in which the inside of the diaphragm senses fuel pressure and the other side senses manifold vacuum. Normal fuel pressure is established by a spring preload applied to the diaphragm. Control of the fuel system is maintained through the EEC power relay and the EEC-IV or EEC-V control unit, although electrical power is routed through the fuel pump relay and an inertia switch. The fuel pump relay is normally located on a bracket somewhere above the Powertrain Control Module (PCM) and the inertia switch is located in the cab. The in-line fuel pump is usually mounted on a bracket at the fuel tank, or on a frame rail. Tank-mounted pumps can be either high or low-pressure, depending on the model.
The inertia switch opens the power circuit to the fuel pump in the event of a collision. Once tripped, the switch must be reset manually by pushing the reset button on the assembly. Check that the inertia switch is reset before diagnosing power supply problems to the fuel pump circuit.

Fuel Pump
The fuel delivery system uses either a high or low-pressure in-line or in-tank electric fuel pump, with some models equipped with both. It is a recirculating system that delivers fuel to a pressure regulating valve in the throttle body and returns excess fuel from the throttle body regulator back to the fuel tank. The electrical system uses two types of control relays, one controlled by a vacuum switch and the other controlled by the powertrain control module (PCM) to provide power to the fuel pump under various operating conditions.

An inertia switch is used as a safety device in the fuel system. The inertia switch is located in the cab, generally under the dashboard on the right side. It is designed to open the fuel pump power circuit in the event of a collision. The switch is reset by pushing each of 2 buttons on the switch simultaneously (some models use switches with only one reset button). The inertia switch should not be reset until the fuel system has been inspected for damage or leaks.
When the ignition switch is ON , it turns the EEC power relay ON . The EEC power relay provides power to the powertrain control module (PCM) and the control side of the fuel pump relay. Power for the fuel pump(s) 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 flows through the fuel pump relay and inertia switch to the fuel pump(s). The fuel pump relay is controlled by the PCM.
When the ignition switch is turned ON , the fuel pump(s) will operate. If the ignition switch is not turned to the START position the PCM will shut the fuel pump(s) OFF after 1 second. The PCM will operate the fuel pump(s) operate the fuel pump(s) when the ignition switch is turn to START position to provide fuel while cranking.
After the engine starts, the PCM will continue to operate the fuel pump(s) unless the engine stops, drops below 120 rpm or the inertia switch is tripped.

1987-89 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.


1990-1996 trucks use a high pressure pump which is part of the modular, In-Tank Reservoir (ITR) assembly. Besides the pump, the ITR consists of a venturi jet pump, a supply check valve and a shuttle selector valve. All this is mounted on the fuel gauge sender flange. The sending unit is separate from the ITR module.

CAUTION
Fuel supply lines on vehicles equipped with a high pressure fuel system will remain pressurized for long periods of time after engine shutdown. The fuel pressure must be relieved before servicing the fuel system.

Relieving Fuel System Pressure
A special tool is necessary for this procedure.
1. Make sure the ignition switch is in the OFF position.

2. Disconnect the battery ground.

3. Remove the fuel filler cap.

4. Using MFI Pressure Gauge T80L-9974-A, or equivalent, at the fuel pressure relief valve (located in the fuel line in the upper right corner of the engine compartment) relieve the fuel system pressure. A valve cap must first be removed to gain access to the pressure relief valve.


VOLUME TEST

1. Operate the engine at the specified idle rpm.

2. Open the hose restrictor and catch the fuel in the container while observing the time it takes to pump 1 pint. 1 pint should be pumped in 20 seconds. If the pump does not pump to specifications, check for proper fuel tank venting or a restriction in the fuel line leading from the fuel tank to the carburetor before replacing the fuel pump.

Go here and sign up then you can look at the repair manual for free
www.autozone.com/autozone/repairinfo/repairInfoLanding.jsp

Thanks for the info...copy and pasted and sent in an email to him. Thanks...somebody rep that man for me.

 

[Skandocious]

You can test the relay to be sure-- put +12V on the power pin then ground the 86 pin, you should hear the relay click. Remove the ground you should hear it click again. If no click-- broken.

 

[LEB Ben]

Thanks Chris...again I'll pass it along, but seeing as Dad doesn't enjoy tinkering much anymore, if it comes to that, I'll do it over Thanksgiving. Again, thanks for all the good info guys.

 

[Skandocious]

Sorry I was on autopilot with that last post, I mean to say put 12v to the 85 pin and ground the 86.

 

[blackhat620]

There is more than one relay, also if there is a problem with the EEC or PCM you will not get fuel flow. In addition, there is a fuseible link in the main power wire to the fuel pump. Not to mention the possibility of a damaged wire. It is going to take a little bit of detective work to determine were the problem is.

 

[blackhat620]

Sorry I was on autopilot with that last post, I mean to say put 12v to the 85 pin and ground the 86.

The coil on a relay does not care which pin is grounded and which pin is power, unless there is a diode across the coil.

 

[Skandocious]

The coil on a relay does not care which pin is grounded and which pin is power, unless there is a diode across the coil.

Yeah I know-- my point was that in the first post I said to put 12v on the "power pin", which is not very specific about which pin that is I corrected myself and specified which pin is the "power pin".

 

[blackhat620]

Yeah I know-- my point was that in the first post I said to put 12v on the "power pin", which is not very specific about which pin that is I corrected myself and specified which pin is the "power pin".

Chris, help me out here, i am still lost with your answer since there is no "power Pin" on the coil of a relay. Pull relay out of socket, apply 12+ to either coil pin (85 or 86) and ground the other. What am i missing?

 

[Skandocious]

Exactly-- you're missing nothing I was trying to post and talk to Trista at the same time and I think in my head I was saying "put power to the 85 pin" but I typed it out as put 12v on the "power pin". There's no such thing as a "power pin" so I came back and corrected myself.

 

[LEB Ben]

Either way, both of you were very helpful and thanks. Dad actually said he was gonna get on it this weekend. Maybe he feels guilty and like he broke it...haha...cuz it didn't have an issue the last 2 weeks.

 

[blackhat620]

Exactly-- you're missing nothing I was trying to post and talk to Trista at the same time and I think in my head I was saying "put power to the 85 pin" but I typed it out as put 12v on the "power pin". There's no such thing as a "power pin" so I came back and corrected myself.

Ah okay, it's all clear now.