Sputters and shuts off when warm

Tiny
JTPFARM
  • MEMBER
  • 1992 FORD F-150
  • 4.9L
  • 6 CYL
  • 4WD
  • MANUAL
  • 150,000 MILES
I recently acquired the truck listed above 5 speed. (For free) It was parked nine years ago simply due to non use. I completely drained the gas. New spark plugs, new fuel filter, new air filter, new fuel pump, new battery. It will start right up and run perfectly smooth. I can drive it about three miles with zero issues. After that it starts to hesitate on acceleration and eventually will shut off. It will start right back up and run smooth until I try to take off. If I try to accelerate in neutral, it spits and sputters. When this is happening, it will take off immediately after restart but then shuts off again. Eventually it will idle a little rough. If I shut it off for a half hour, It will start right up and run perfect. It can be up to normal operating temperature sitting still and run fine. Even after holding at 2,000 RPM's for a few minutes. As soon as I drive 1000' under hard acceleration, the problem immediately returns.

If I bang on the fuel tank, the issue will improve (it seems) but not go away. That is what led me to the fuel pump but its still the exact same issue.

I don't have a service engine light on. But have memory code 172.

Any ideas?
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Saturday, April 20th, 2019 AT 12:57 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

Have you already replaced the fuel pump? Also, was the filter replaced at the same time? It sounds like you are picking up dirt, restricting the fuel flow, and then when it's off, things settle and it runs good until it happens again. What I would recommend is to actually check fuel pump pressure under these conditions to see if there is an issue. Also, another common issue with these vehicles was the ignition control module. It is a box mounted on the firewall. They get hot and fail.

Here are directions for replacing the module. Picture 1 correlates with these directions.

________________________________________________

PROCEDURES
Ignition Module

picture 1

1. Remove the two Thick Film Ignition (TFI) module/heatsink assembly retaining screws.
2. Disconnect the TFI module electrical connector.

NOTE: To disconnect the module connector, push on the connector where it says PUSH, then slide connector from module.

3. Remove the TFI module/heatsink assembly from the vehicle.
4. Remove the two TFI module retaining screws and separate the module from the heatsink.
5. Clean the mating surfaces, then apply dielectric silicone (Ford D7AZ-19A331-A, or equivalent) to the ignition module base.
6. Place the module in the heatsink assembly, then install and tighten the retaining screws to 15-35 in lb (1.7-4.0 Nm).
7. Install the TFI module/heatsink assembly on the fender and install the retaining screws.
8. Connect the TFI module electrical connector.

______________________________________

Here is a link that shows how in general to test fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

_____________________________________

That is where I would start. However, I have a feeling there is still dirt in the tank causing the issue. If the pump wasn't replaced, let me know.

Also, let me know what you find or if you have other questions.

Take care,
Joe
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Saturday, April 20th, 2019 AT 8:45 PM
Tiny
JTPFARM
  • MEMBER
Thank you for your response. Yes, I replaced the fuel pump and filter. Immediately after that the exact same problem remained as before.

I also believe it's a fuel delivery problem, but I am lost as to what else it could be. The tank was spotless inside and very little dirt came out of the old filter.

Keep in mind that this pickup sat unstarted for almost ten years.
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Saturday, April 20th, 2019 AT 8:56 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Have you checked pressure to confirm the regulator is working? It is vacuum operated and may be bad or there could be a vacuum leak. Too much pressure can cause this type of problem too. See the picture for location.
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Saturday, April 20th, 2019 AT 9:32 PM
Tiny
JTPFARM
  • MEMBER
I plan to check fuel pressure next week sometime. I will report back on what I find.

Thanks again.
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Saturday, April 20th, 2019 AT 10:16 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:

You are very welcome. Let me know what you find.

Take care,
Joe
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Sunday, April 21st, 2019 AT 5:51 PM
Tiny
JTPFARM
  • MEMBER
Ok, I have done a pile of testing. The fuel pressure slowly drops off when the problem occurs. All the way to zero. I found that the fuel pressure regulator was bad so I replaced that first. No help. I have finally resorted to setting a battery in the box and running direct power to the fuel pump. I thought this would absolutely cure the problem and that I had a ground issue. NOPE! It does the exact same thing. Fuel pressure drops off but ONLY after I put it under load. (Even if only for 50') And even with a battery still hooked directly to the pump. The weird part is that the fuel pressure stays at zero even though I can still hear the pump running. If I unhook the pump for a split second and hook it back up, the pressure immediately returns. I am extremely stumped on this one!
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Tuesday, April 30th, 2019 AT 3:58 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:

If the fuel filter is good, you need to remove the pump to determine if anything is getting picked up by the pump causing it to loose pressure. If there isn't, replace the pump. Even though you hear it running, it may not be pumping. Also, I have seen conditions where dirt have drop to the bottom of the tank with the engine off and when it is started, the pump slowly gets blocked. However, if I had to remove the tank to access it, I would just replace the pump.

Here are the directions:

FUEL PUMP REPLACE
CAUTION: Fuel supply lines remain pressurized for long periods of time after the engine is shut down. This pressure must be relieved before the fuel system is serviced. The fuel system on these vehicles is depressurized by disconnecting the inertia switch and cranking the vehicle for a minimum of 15 seconds.

REMOVAL

1. Depressurize fuel system.
2. Remove fuel from fuel tank by pumping out through filler into a suitable storage tank. Use care to prevent combustion from fuel spillage.
3. Remove fuel tank to bench.
4. Remove any dirt that has accumulated around the fuel pump attaching flange so that it will not enter the fuel tank during procedures.
5. Turn the fuel pump locking ring counterclockwise with the fuel tank lock ring wrench tool and remove locking ring.
6. Remove the fuel pump and bracket assembly.
7. Remove seal gasket and discard.
8. If necessary, disconnect spade connector and remove two screws and fuel sending unit.

INSTALLATION

1. Clean the fuel pump mounting flange and the fuel tank mounting surface and seal ring groove.
2. Put a light coating of grease on a new seal ring to hold it in place during assembly and install it in the fuel ring groove.
3. Install fuel pump and sender assembly carefully to ensure that the filter is not damaged. Be sure that the locating keys are in keyways and the seal ring remains in place.
4. Hold the fuel sender and sealing gasket in place, install and rotate the locking ring clockwise until stop using fuel tank lock ring wrench tool.
5. Install the fuel tank in vehicle.

____________________________________________

The fuel tank needs removed to replace the pump. Here are the directions for that process.
The attached pictures correlate with these directions.

MIDSHIP FUEL TANK
STEEL MIDSHIP FUEL TANK

pic 1

pic 2

Removal

NOTE: As there are different midship tank installations which are removed and installed essentially the same way, follow steps and refer to appropriate illustration for details.

1. Disconnect battery ground cable.

NOTE: On vehicles equipped with EEC, when the battery has been disconnected and reconnected, some abnormal drive symptoms may occur while the EEC processor relearns its adaptive strategy. The vehicle may need to be driven 10 miles or more to relearn the strategy.

2. Using Rotunda 034-00001 Fuel Storage Tanker or equivalent drain fuel tank.
Drain both tanks on dual tank vehicles.
3. Raise vehicle on hoist.
4. If equipped with skid plate, remove fasteners and remove skid plate assembly.
5. Loosen clamps and disconnect fuel filler hose and overflow hose at tank.
6. Position suitable jack under tank.
7. Remove nuts and bolts and lower straps.
If necessary, turn strap approximately 30 and remove.
8. Lower tank enough to gain access to fuel connections.
9. Disconnect fuel delivery module (FDM) electrical connector.
10. Disconnect fuel vapor hose(s) from port valve(s).
If equipped, remove vent hose from clip on frame.
11. Disconnect fuel supply and return lines according to instructions for push connectors in this section.
12. Take out fuel tank.
13. If necessary, remove retaining ring with Fuel Tank Sender Wrench D84P-9275-A or equivalent then remove FDM and gasket. Fuel gauge unit may be separated from fuel pump and reservoir assembly.

Installation

pic 3
- For installation procedures, follow the removal procedures in reverse order.
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Tuesday, April 30th, 2019 AT 7:02 PM
Tiny
JTPFARM
  • MEMBER
Thanks for the reply. I have already replaced the fuel pump and have the exact same issue. When I replaced the pump I also completely drained the tank out and made sure it was clean. The new pump is giving me the EXACT same symptoms as the old one. And it absolutely will not act up until the engine has a load on it. I can rev the engine or hold RPM as long as I want and never lose fuel pressure.

When it does lose pressure, a split second of cutting the power to the pump and the pressure goes right back up.
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Tuesday, April 30th, 2019 AT 10:13 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Since you ran power and it does the same thing, confirm there is a good ground to the pump. And again, something must be moving in the tank and restricting flow. That is really an odd one. You know, I'm sitting here thinking of what could cause it when under a load. When it is under a load, the vehicle is moving. I wonder if it has something to do with the inertia switch. It is designed to shut fuel off if there is an accident. There is a steel ball in the switch which is held in place by a magnet. Perhaps something happened and the ball is no longer being held. Take a look through this description.

Typical Inertia Fuel Shut-Off Switch

See Pic 1

PURPOSE
The inertia switch is used to shut the fuel pump "Off" in the event of a collision.

CONSTRUCTION
The inertia switch consists of a steel ball held in place by a magnet.

OPERATION
When a sharp impact occurs, the ball breaks loose from the magnet, rolls up a conical ramp and strikes a target plate. This opens the electrical contacts of the switch and disrupts power to the electric fuel pump. The engine will quit running within a few seconds after the fuel pump loses power. The inertia switch must then be manually reset before the engine can be restarted.

WARNING: DO NOT reset the inertia switch button if you see or smell fuel.

___________________________________________

The inertia fuel shutoff switch is on the right cowl panel, just forward of the door, and below the instrument panel. Take a look at pics 2 and 3.

If you look at picture 4, it shows a test for the switch. Check that.

__________________________________________

Next, make sure the pump has a good ground. Pic 5 shows that process.

Let me know if any of this helps.

Joe
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Wednesday, May 1st, 2019 AT 6:38 PM
Tiny
JTPFARM
  • MEMBER
I FINALLY found the issue. The new fuel pump was bad! It would build pressure but had hardly any volume. I put a second new pump in and all is good.

Thanks again for your help!
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Thursday, May 2nd, 2019 AT 3:31 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Go figure. It sounds like you have the same type of luck as me. LOL Regardless, I'm glad you got it taken care of and you're back on the road.

Take care,

Joe
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Thursday, May 2nd, 2019 AT 7:50 PM

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