fuel pump/inertia switch issue - Mustang Evolution

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Old 03-25-2012, 08:36 PM   #1
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fuel pump/inertia switch issue

Hello, I have been trying to diagnose a fuel pump issue with my 91 stang. No fuel pump priming is hear when key on. There is power input to the inertia switch (thus eliminating all relays, ecm, wiring to the pump as a problem). There is no output from the inertia switch. I bypassed the switch and the voltage went from 12v to 0v as soon as I jumped the two wires. I went ahead and replaced the fuel pump...still same issue. Any one have any ideas??
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Old 03-25-2012, 08:44 PM   #2
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Re: fuel pump/inertia switch issue

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Originally Posted by capnzzz View Post
Hello, I have been trying to diagnose a fuel pump issue with my 91 stang. No fuel pump priming is hear when key on. There is power input to the inertia switch (thus eliminating all relays, ecm, wiring to the pump as a problem). There is no output from the inertia switch. I bypassed the switch and the voltage went from 12v to 0v as soon as I jumped the two wires. I went ahead and replaced the fuel pump...still same issue. Any one have any ideas??
Sounds like you blew a fuse or the fusible link.
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Old 03-25-2012, 08:48 PM   #3
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Re: fuel pump/inertia switch issue

Wiring Diagram

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Old 03-25-2012, 09:03 PM   #4
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Re: fuel pump/inertia switch issue

Thanks for the reply..but according to the diagram there is only one input stream into the fuel pump..so if there is power at that point I believe it would eliminate the fuse/fuseable links as well..confused
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Old 03-25-2012, 09:30 PM   #5
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Re: fuel pump/inertia switch issue

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Thanks for the reply..but according to the diagram there is only one input stream into the fuel pump..so if there is power at that point I believe it would eliminate the fuse/fuseable links as well..confused
There are 2 power supplies that enable the pump to function.
When you first turn on the key it feeds power to the PCM relay which in turn sends power to the numerous solenoids, sensors and fuel injectors, including the fuel pump relay coil.


The fuel pump relay coil is grounded from the control module.
The fuel pump relay should only be grounded by the module and close the contacts feeding power to the fuel pump when the ignition key is on.


The power from the fusible link feeds through the fuel pump relay contacts into the control module and into the inertia switch.
If your power went to 0 when you bypassed the inertia switch then you likely burnt up the fusible link or something in the control module.
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