Rom relay bad, inertia switch melted. What to do?

[Delorean3610]

I found that my fuel pump wouldn't work recently, and the culprits look to be a bad relay and a melted inertia switch.

I have already ordered replacements and plan to install them.

I also believe I will try to clean up my connections, fuse box, and body grounds.

Does anyone have any other suggestions to prevent the same thing from happening again.

[Chris 16409]

I don't know if this will prevent future melting, but I ran a dedicated ground wire from the inertia switch to the frame. The pump is grounded with a bunch of other accessories, so it was suggested that a dedicated ground might help things. I grounded my new wire to one of the bolts that attaches the shifter plate to the frame.

You can jumper the inertia switch plug to verify the pump will still operate.

[DMC5180]

I found that my fuel pump wouldn't work recently, and the culprits look to be a bad relay and a melted inertia switch.

I have already ordered replacements and plan to install them.

I also believe I will try to clean up my connections, fuse box, and body grounds.

Does anyone have any other suggestions to prevent the same thing from happening again.

Some photos would help us see what you are dealing with. Especially the connectors. Want does your fuse box look like at fuse 7.


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[Bitsyncmaster]

I don't know if this will prevent future melting, but I ran a dedicated ground wire from the inertia switch to the frame. The pump is grounded with a bunch of other accessories, so it was suggested that a dedicated ground might help things. I grounded my new wire to one of the bolts that attaches the shifter plate to the frame.

You can jumper the inertia switch plug to verify the pump will still operate.

Using better wire (and your new ground) will reduce the voltage drop to the pump and therefor increase the current a little. The fuel pump draws more current as the voltage it gets goes higher.

That ground wire you did was to eliminate the ground drop to the instrument cluster and give you better instrument readings (the volt gauge).

[David T]

Lots of things go wrong with the electrical fuel pump circuit. Usually starts with a bad fuel pump that draws too much current. The inertia switch was recalled so make sure you got it. The #7 fuse melts out of the fuseblock. The wiring harness plug up by the windscreen washer bottle gets corroded and the connections go bad. The RPM relay overheats and melts down. Water gets past the cover boot and lays on the fuel pump and rots the connections. A bad RPM relay and inertia switch is often caused by a bad fuel pump so just replacing them isn't fixing the problem.

[Delorean3610]

Cool, thanks for responding guys.

But what do I do? I have a new relay and switch on the way and if the fuel pump is bad they will just break again.

Step by step instructions would be nice.

And I will post pictures later when I get home, but right now I have the fuel pump cover off and the rear shelf open.

I have a garage full of tools with a lift. And I recently got my associates degree in electronics engineering. I can do anything with proper instructions.

[Bitsyncmaster]

Cool, thanks for responding guys.

But what do I do? I have a new relay and switch on the way and if the fuel pump is bad they will just break again.

Step by step instructions would be nice.

And I will post pictures later when I get home, but right now I have the fuel pump cover off and the rear shelf open.

I have a garage full of tools with a lift. And I recently got my associates degree in electronics engineering. I can do anything with proper instructions.

The fuel pump normally draws about 7 amps. Best thing to do is make sure all the connectors are clean and tight. Hard to clean the female pins but the male pins can be sanded bright.

[PJ Grady Inc.]

Cool, thanks for responding guys.

But what do I do? I have a new relay and switch on the way and if the fuel pump is bad they will just break again.

Step by step instructions would be nice.

And I will post pictures later when I get home, but right now I have the fuel pump cover off and the rear shelf open.

I have a garage full of tools with a lift. And I recently got my associates degree in electronics engineering. I can do anything with proper instructions.

In the case of the inertia switch all 81's had a defective part which was recalled. They virtually all fail with the external sign being melted plastic visible between the switch terminals. The later (two part #'s) switches do not fail in my experience. Please see my answer to "Pump works, getting no power" for more info on the inertia switch.
The NOS fuel pump relay also has a high failure rate so we don't replace those with NOS. We also carry the later inertia switches.
Rob

[SS Spoiler]

Huh?...went and looked at my inertia switch and found
it had been jumpered 30 years ago. No wonder iv'e had
no problems with it!


lonely guy in Montana

[David T]

Huh?...went and looked at my inertia switch and found
it had been jumpered 30 years ago. No wonder iv'e had
no problems with it!


lonely guy in Montana

The inertia switch is an integral safety device and should only be jumpered for testing purposes. It is meant to turn off the fuel pump in the case of an accident and (if the Central Locking System is working) unlock the doors.