Fuel pressure

Tiny
PAPA ED
  • MEMBER
  • 1988 DODGE TRUCK
  • 5.2L
  • V8
  • 2WD
  • AUTOMATIC
  • 91,000 MILES
Truck is hard to start in morning and after sitting awhile. It is very hard to start in a hot restart situation after sitting just a few minutes runs good after it starts. Fuel pressure is 15 lbs, but falls instantly as ignition is turned off. Pulling vacuum hose off regulator has no effect. When running has no vacuum at hose. Applying vacuum to regulator immediately shuts off the engine. Pinching off fuel return line raises pressure to 20 lbs fuel pump and relay are both new.
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Monday, July 3rd, 2017 AT 9:44 PM

4 Replies

Tiny
JIS001
  • EXPERT
Problem looks like it is the fuel pump at this point. Replace the pump and strainer and let us know how it goes.
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Tuesday, July 4th, 2017 AT 3:01 AM
Tiny
PAPA ED
  • MEMBER
I know you can get a bad one, but this pump is new so is the strainer and the fuel pump relay. This model only carries 14.5 lb of pressure and it has that and goes up past 20 if you pinch the return line pumps do not run on these early models. When you first turn on the ignition it must see oil pressure or ignition impulse before it runs I have tried to find out if there was a kit to make it like the later models that would run for eight or ten seconds when you turn on key. My local Dodge Dealer told me they did not have anybody that would know about one that old and could not look up a recall or modification from that far back. I have a 1998 model with a 5.9 and the pump runs as soon as you turn on the key and it starts instantly every time hot or cold. I have checked the power to the pump relay and it is hot at all times and the pilot is hot with the key on and energizes with ground from somewhere that is not there, until it sees a signal from somewhere else if I jump the relay the pump runs and it starts instantly, but this could be a fire hazard in the right situation.
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Tuesday, July 4th, 2017 AT 11:00 AM
Tiny
JIS001
  • EXPERT
The fuel pump could still be bad. There should be a check valve built into the unit to prevent the fuel from draining back. Here is the fuel pump description per Chrysler.

An electric fuel pump is located in a specially designed reservoir within the fuel tank. The reservoir ensures that fuel is available at the pump inlet during all operating conditions, particularly when little fuel remains in the tank. The fuel pump is energized by the ASD relay and operates whenever the relay is activated. Fuel is drawn into the pump through a sock type' filter screen, and the pump contains an integral fuel inlet check valve to prevent drain back.

If you only replaced just the fuel pump I would recommend you replace the whole module as an assembly if the part is still available. Also check the fuel supply line in the unit to see if it broke causing a leak. Attaching bulletin and a pic they provided.

No start, surge or hesitation due to insufficient fuel supply to the throttle body. This condition may be caused by a ruptured fuel supply hose at the in-tank fuel pump module.
DIAGNOSIS
Before performing the diagnosis for the above SYMPTOM/ CONDITION, perform the Fuel System Pressure Release Procedure as called out in the "Fuel System" section of the appropriate 1988 or 1989 service manual.
The following procedure will help in diagnosing a ruptured fuel pump supply hose.
1.
Disconnect the fuel supply hose from the throttle body.

2.
Connect fuel system pressure tester, Miller Tool C-4799-A, to the fuel supply hose.

3.
Connect DRB II diagnostic tester to the vehicle connector. Turn the ignition key to the "Run" position. Cycle the DRB II to the Actuate Outputs Test for "Auto Shutdown Relay." This will activate the fuel pump and pressurize the system.

4.
The pressure gauge should stabilize at 100 Kpa +/- 7 Kpa (14.5 psi +/- 1 psi).

5.
Clamp the fuel return hose shut at the throttle body. The fuel pressure will increase and stabilize at approximately 345 Kpa (50 psi).
6.
Turn the ignition to the "OFF" position.

7.
If the fuel pressure drops slightly (less than 5 psi) and then stabilizes, the system is operating correctly.

8.
If the fuel pressure drops rapidly (to below 10 psi in one minute or less) a leak is present in the fuel supply system.

9.
If no leaks are visible between the fuel tank and the throttle body, the problem is most likely a ruptured fuel supply hose at the fuel pump module.

10.
Remove the fuel return hose clamp and the fuel pressure tester

REPAIR PROCEDURE

This procedure outlines the replacement of the fuel supply hose at the fuel pump module.
1.
Remove fuel tank assembly from vehicle.

2.
Remove fuel pump module from fuel tank.

3.
Using service manual procedures (Page 14-4 of 1989 Rear-Wheel-Drive Truck Manual # 81-370-9008), disassemble fuel pump module assembly just to the point of being able to remove the fuel supply hose from the fuel pump module lid (Figure 1).
4.
Remove fuel supply hose from fuel pump.

5.
Remove pump mounting bracket and rubber collar from hose. Discard hose and clamps.

6.
Slide clamps included in package onto new supply hose (see "PARTS REQUIRED" for application). Install supply hose with the short end attached to module lid. Attach fuel pump to supply hose. Tighten clamps to 1 N-m (10 in. Lbs.).

7.
Install pump mounting bracket and rubber collar on hose, positioning bracket just under locating clamp on hose.

8.
Reassemble module.

9.
Install module into fuel tank and install fuel tank in vehicle.

10.
Start vehicle to check for fuel leaks and to verify proper operation.
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Thursday, July 6th, 2017 AT 9:52 PM
Tiny
JIS001
  • EXPERT
This is the part numbers you can try ordering but they may not be available anymore?

1 Fuel Supply Hose (B/AB) P/N 52006220
1 Fuel Supply Hose (D/AD, N/AN) P/N 52006219
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Thursday, July 6th, 2017 AT 9:58 PM

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