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Unread 11-02-2005, 07:58 PM   #1
rich2481
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Join Date: Oct 2005
Posts: 32
inertia switch

1994 Grand Cherokee Laredo 2WD, looking for the inertia switch before I tear into gas tank, Son drove it one weekend, came home no problems, and I tried the following week and no start,. no gas to fuel rail, tried swapping same part number relays in fuse block, no start, still no gas,

heard was a Federal law to have interia switch in fuel injected vehicles, another site said under the passenger seat, only thing there is a small connector, same one under drivers seat, I figure power seat connector, I looked in side kick panel of passenger side, just a big connector,

can someone shed some light on where it would me

Thanks in advance, Jeep has sat for two months, no time, need emissions in December so I either find it quick or off to the shop it goes,
thanks

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Unread 11-02-2005, 08:14 PM   #2
mr_user
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Rich,

I am assuming by "Inertia Switch" you mean some sort of fuel cutoff device in the event of a rollover. Though there hasn't really been too much talk about such a device here on the forum, on the radiator support in the front of the engine bay there is a diagram that illustrates a "Fuel Shutoff Valve."

Have you thought the culprit might be the fuel pump itself? It is an extremely common problem especially on the ZJ's. You have taken all the initial steps to diagnosing no pressure at the rail, really the only component I can think of that could be the culprit is the fuel pump itself. Swapping out the pump for an OEM unit is around three hundred dollars with self-labor and necessitates dropping the fuel tank for access.

Try searching for "Swampy Bypass," it was a mod done by a member here that relocates the pump to outside of the tank and also allows you to use an aftermarket unit which is much cheaper.


Matt
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Unread 11-02-2005, 08:15 PM   #3
jeepholic
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It's under the rear seats, I think it has an arrow on it, sounds like you have a dead pump.
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Unread 11-03-2005, 07:04 AM   #4
Meerkat
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The inertia switch is mounted to the floor under the driver's side rear seat near vehicle centerline.
However, the function of the switch is tied to air bags and not fuel delivery.
With no fuel to the rail, it's for sure your pump isn't working. You need to establish if there is power to the pump or not.
The auto shut down relay may be what you are thinking of as an inertia switch. If there is no power to the pump, your next step is to check the ASD for proper operation, that is, determine what is causing the ASD to shut down power to the pump.

HTH
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Unread 11-03-2005, 07:08 AM   #5
greasefingers
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Turn the ignition switch to the Run position only (not the Start position). Listen for the fuel pump motor to make whining sound in the gas tank. If you have a fuel pressure gage, then check for approx 30 to 40 psi at the fuel rail. If you hear nothing then disconnect the electrical connector, at the tank, and check for a 12 volt supply coming from the engine end of the harness. If 12 volts is present then check for continuity across the fuel pump. If no resistance or mega-ohms, then the fuel pump motor is most likely dead. If so then drop the tank and replace it.
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Unread 11-03-2005, 08:11 AM   #6
rich2481
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I had the wife turn the key on while I had the hose disconnected at the rail, no fuel, I can make the truck run with carb cleaner, there is no fuel pump hum when I climbed under there with her turning the key on, I also noticed with my test light that the frame on the Jeep is not grounded, but someone made the comment that grounds were in the wire harness now and possibly the frames are not grounded anymore,

with my research online I was under the assumption that Federal law required a inertia switch in the event of a roll over or a head on to shut the pump off.

thanks for the input,
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Unread 11-03-2005, 08:29 AM   #7
Dr. Righteous
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ZJ don't have a inertia switch in the same sense as other vehicles. Like Mustangs, if you get hit or even hit a pothole sometimes it will trigger the inertia switch. In Jeeps it is tied to a serious accident that deploys the airbag.
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Unread 11-03-2005, 08:34 AM   #8
Jeep-Tech1
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Ther is no inertia switch on a jeep! you probably have a fuel pump problem. And while you have the tank down take it and have it cleaned out real good. What happens is that the rotor in the fuel pump binds and comes apart spilling metal shavings in the fuel and then inturn when the new pump fires up and the rotor in the new pump gets hot the metal shavings stick to the new rotor a when it cools down it's now stuck. Been thru this a hundred times. Was replacing fuel pump after fuel pump until we started cleaning the tanks out. Hope this helps.....
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Unread 11-03-2005, 08:44 AM   #9
Dr. Righteous
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Quote:
Originally Posted by Jeep-Tech1
Ther is no inertia switch on a jeep! you probably have a fuel pump problem. And while you have the tank down take it and have it cleaned out real good. What happens is that the rotor in the fuel pump binds and comes apart spilling metal shavings in the fuel and then inturn when the new pump fires up and the rotor in the new pump gets hot the metal shavings stick to the new rotor a when it cools down it's now stuck. Been thru this a hundred times. Was replacing fuel pump after fuel pump until we started cleaning the tanks out. Hope this helps.....
WOW, knowledge is power.
I have heard of several accounts of repeat fuel pump failures. This explains why.
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Turbocharge it!
Then I'm interested!
'94 ZJ Limited Lifted and LOCKED!
'04 Durango Limited (the wife mobile)
'72 Plymouth Satellite Sebring Plus (Resto MoPar)
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Unread 11-03-2005, 08:52 AM   #10
greasefingers
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There is a roll-over ball check valve. It is on top of the gas tank.

You really need to confirm that 12 volts is making it to the fuel pump before being absolutely positive that the pump is at fault. You do not need to drop the gas tank to do this. The harness connector extends about 18 inches from the gas tank
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88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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