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Jim
Jim, ASE Certified Technician
Category: Mercury
Satisfied Customers: 1188
Experience:  ASE Certified A6,A8,L1 and California Licensed Smog Technician
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99 Mercury Mystique: fuel problem..fuel pump relay..inertia switch

Customer Question

I have a 99 Mercury Mystique that has a fuel problem. When I turn on the ignition to start the engine, the fuel pump does NOT run. I have changed the fuel pump relay, checked the inertia switch and checked the fuse. The fuel pump still will not come. I have the fuel pump out of the tank but still hooked to the cars wiring so i can feel that it is not running. Somebody please help.
Submitted: 5 years ago.
Category: Mercury
Expert:  Jim replied 5 years ago.

Jim :

To isolate the problem the following test will need to be done.1. Check power to the Fuel Pump Driver Module (FPDM) on the Blue (BL) wire from the inertia switch. This circuit should show battery voltage with the key in the run position.

2. Check the Black (BK) wire of the FPDM for a good ground.

3. Check the Blue/White (BL/WT) wire of the FPDM for battery voltage with the key on. This circuit provides power to the fuel pump from the FPDM when the ignition switch is on.

4. Backprobe the Blue/Black (BL/BK) wire of the FPDM with a jumper wire. Ground this circuit with the ignition switch on and a fuel pressure gauge installed at the fuel pressure rail. When grounding this circuit, fuel pressure should exceed 70 PSI at the fuel injection rail.

5. If all circuit voltage checks OK, but fuel pressure does not meet the specification in step 4, replace the fuel pump

Customer:

where is this FPDM located

Jim :

located behind luggage compartment lining, LH-side

Customer:

ok i will check

Jim :

ok, let me know if you need more help

Customer:

ok

Expert:  Jim replied 5 years ago.
Thank You for using just answers.
Customer: replied 5 years ago.
I am not getting any power to the FPDM with the ignition switch on. Gotta bew something else
Expert:  Jim replied 5 years ago.
Tell me which wire color you are checking and what kind of reading you are getting?
Customer: replied 5 years ago.
There are six wires in the connector. wh/bl stripe, green/or stripe, bl/pu stripe, black, brn/yel stripe, g/bl stripe. I get nothing on any wire except on g/or stripe and it reads 9.0 vdc(battery may be low)I also checked the voltage on the inertia switch and am getting app. 9.0 vdc in and out. any ideas? Larry
Expert:  Jim replied 5 years ago.

The inertia switch powers up the fuel pump driver module, so if you are getting that power to the module from the inertia switch, then check the black wire for ground, do you have ground to the module? When you have both power and ground to the module then the module will send power to the pump step #3

3. Check the Blue/White (BL/WT) wire of the FPDM for battery voltage with the key on. This circuit provides power to the fuel pump from the FPDM when the ignition switch is on. No power out bad module.

Jim and 4 other Mercury Specialists are ready to help you
Customer: replied 5 years ago.
ok let me check
Customer: replied 5 years ago.
Jim, I appreeciate all of your help. I know we were heading in the right direction so i am accepting your answer but i am calling a mobile mechanic to come and fix it. again, i appreciate all of your help. Thanks larry
Expert:  Jim replied 5 years ago.
Let me know if you need anymore assistance.

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