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Old 09-03-2009, 04:58 PM
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Fuse keeps blowing

Mallory 140 fuel pump. First started off as no power and I knew I needed brushes so, I replaced them. Found fuse blown, replaced. Pump looked great inside no problems. It will run for 3-5min, wire gets hot and the fuse will blow. Pulled it apart found nothing, spins freely, checked ground, seems fine. If I can get it going and drive it immediately the fuse doesn't blow, only at idle.
Any help is appreciated.

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Old 09-03-2009, 05:19 PM
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Is this a new installation, or a previously used set-up now showing problems??

What gauge wire feeds the pump and ground wire,and how long is the wire length?? How is the pump grounded??

Resistance(fuel pressure) loads the pump motor harder at idle due to backpressure(very little is being used at the engine), raising the current draw in the pump, especially with a dead head regulator. What regulator are you using??
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Old 09-03-2009, 05:29 PM
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This has been in the car, it's not new. 12g wire that's 12" long. It's grounded to the mounting bracket, which is the frame. Mallory regulator 4207 I think.
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Old 09-03-2009, 05:32 PM
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Quote:
Originally Posted by ericnova72
Is this a new installation, or a previously used set-up now showing problems??

What gauge wire feeds the pump and ground wire,and how long is the wire length?? How is the pump grounded??

Resistance(fuel pressure) loads the pump motor harder at idle due to backpressure(very little is being used at the engine), raising the current draw in the pump, especially with a dead head regulator. What regulator are you using??
The flow of fuel could also be acting as a coolant. Lack of flow at idle will affect the cooling.
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Old 09-03-2009, 06:07 PM
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What gauge and how long is the feed wire?? Wire gauge of entire cicuit, both before and after the switch?? Are you using a relay??

Filter before or after the pump?? Has it been serviced lately??
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Old 09-03-2009, 06:29 PM
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As I stated before it's 12gauge and it can't be any longer than 18" total. Yes there is a relay. Fuel filter is before the pump and clean as Whistle.
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Old 09-03-2009, 06:42 PM
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It is a resistance issue so it may be internal to the pump windings. You may also want to try a fresh relay, I've seen them cause issues with nitrous systems solenoids with a similar amp draw.

Another thought is to temporarily rig the pump outlet back into the cell and let the pump run free for 15-20 minutes (if it will) to bed in the brushes.

Also, there are two different types of brushes, plain carbon and copper impregnated carbon. I don't remember which Mallory uses, but if the wrong type is used it will cause a problem that I seem to remember strikes me like yours??

Just throwing out ideas now.
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Old 09-03-2009, 08:07 PM
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Alright thanks, I think I'll try another pump and see what happens.
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