LUVTruck.com

So here is the basics. 1980 4x4 bone stock. I turn the key to the ON position and I can hear my fuel pump working. Turn the key to start and the starter cranks the engine just fine and it runs just fine, but as soon as I let the key back to the ON postion the engine dies. Also if the key gets left in the ON postion there is a clicking noise. It comes from what I believe is the Fuel Pump Relay. It's a little silver box with 5 prongs on it on the passenger fender. I replaced twice with 2 different ones from the junk yard, but it still makes the clicking noise. I've also replaced my ignition switch in the dash. I'm outta idea. anybody got something?

The problem with keeping the motor running is most likely at the ballast resistor. It's either bad or you're not getting power to it. There's a fuel pump relay and a resistor bypass relay. They both are found under the metal cover on the passenger side fender. Apparently the bypass relay is working because the engine will fire in start mode.
Check to see if the ballast resistor is good. If it turns out that the either relay is bad, you can adapt a 40 amp bosch relay instead of getting a used original unit.

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Previous setup: 4.1 Buick V-6/TH 350
Current setup: 400 Small Block Chevy V-8/TH 350
9" ford rear end/short bed/blue
What do Water, Electricity and Humans have in common... They all travel the path of least resistance.

Is the ballast resistor the little thing that sits next to the voltage regulator?

It sits on top of the coil, on the right fender well. A little white porcelain thing.

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OK, I'm over it. Where's the beer?

If it is original it is a little metal box instead of a porcelin deal, but it should be right on top of the coil. To test it, connect a wire from the battery + post to the resistor (on the side away from the coil) and if it stays running the resistor is good but its power source is not. If it stays the same, the resistor is bad.

The fuel pump should not run with the key to ON unless the motor is running. It sounds like you have some electrical gremlins going on somewhere. The alternator and voltage regulator activate the fuel pump and resistor bypass relays, so you may have a charging issue going on too.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Your right 800. Thanks for the correction.

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OK, I'm over it. Where's the beer?

Nah, not a correction, just more information. An old truck is just as likely to have a generic replacement ballast resistor as it is the stock original part. Shoot, that part is one of my road spares, always carry one in the truck with me.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Fuel pump I don't believe is original and it's wired up to just always run when the key is on. Not really a big deal. I'll have to look around for the ballist because I know the coil was replaced with the larger Accel coil.

IT was in fact the ballast resistor. Thanks for the help

When I went to look at my first 4x4 LUV it would fire when cranking and then die. I got it nice and cheap because of that, put in a spare resistor, and drove it home. It is a simple, cheap little part, but if it isn't working niether is your truck. Glad you got it going again.

_________________
95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

I'm new to this, so I gotta ask.

If you turn the key to on, and the fuel pump doesn't turn on, how to you get fuel to the carb?

I don't understand the difference in circuit operation between truck running and truck not running, with key to on. That's the position the key has returned to after actuating the starting circuit.

It has to do with the alternator/voltage regulator. The relay gets a signal from the charging system. If the motor stops running, the charging system isn't active so the pump doesn't work. It will send a signal while cranking.

_________________
Previous setup: 4.1 Buick V-6/TH 350
Current setup: 400 Small Block Chevy V-8/TH 350
9" ford rear end/short bed/blue
What do Water, Electricity and Humans have in common... They all travel the path of least resistance.

The chevy vega uses the starter solenoid to get power to the fuel pump while starting then the fuel pump works off the oil pressure sending switch to keep running. That way if the motor quits running no oil pressure is present and the fuel pump stops running.

My truck is fairly unmolested, and when I turn the key on, the fuel pump comes on.