Fuel Pump Fuse Blows all the Time now! - Defender Source
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Old February 26th, 2006, 12:55 PM
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Fuel Pump Fuse Blows all the Time now!

Alright, Same problem as before.....
When I turn off the ignition after a short or long drive, the fuel pump fuse(7.5A) snaps. I deliberately bought like 10 of them to keep swapping in fresh ones during each session of troubleshooting. Here is what I found out:

By the way, I changed the Start Relay and the Fuel Pump Relay recently, so I eliminated them from the equation (I Think).

When the engine is running, I can pull the Fuel Pump fuse and look at it. It is still a good fuse. The fuel pump is still working and the engine doesn't die. When I replace the fuse and then shut off the engine with the key, the fuse snaps (breaks). Subsequent starts don't work with a broken fuel pump fuse in the fuse panel. No suprises there.

When I put in a fresh fuse, the engine cranks, etc. Here's where it gets weird: I can pull the fuse (it's still good) and shut the engine off with the key, since no fuse is installed, no fuse breaks...right? Well, while the engine is warm I can crank it back up and run with no fuel pump fuse installed at all! The fuel pump works just fine.

What it seems to me like is this: The fuse panel either wants a good fuse or no fuse installed, but never a broken fuse. WTF? Is there some risk of melting something somewhere along the line with no fuel pump fuse installed? I'm really confused. I'm not sure if it's the same problem as Mike Hill's from 2004.

Any thoughts? I'm tired of driving around with a pocket full of 7.5 amp fuses for every trip.
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Old February 26th, 2006, 02:26 PM
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Well,

It it were me, I would throw in a 20 amp and call it a day. Do you have dual batteries by any chance?
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Old February 26th, 2006, 09:21 PM
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Nope. Single Battery, but very interested in going dual (sorting out a winch bumper currently).

So...would the 20 amp fuse be more of a burning/melting hazard than the 7.5?
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Old February 26th, 2006, 09:47 PM
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Quote:
Originally Posted by thug1313
Nope. Single Battery, but very interested in going dual (sorting out a winch bumper currently).

So...would the 20 amp fuse be more of a burning/melting hazard than the 7.5?
Yeah, I would think so, but I have been using larger amp fuses in all sorts of stuff for a long time with no issue. Probably not the answer you were looking for!
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Old February 28th, 2006, 08:28 AM
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When this happened to Jimmy's it was a bad fuel pump! I would try unplugging the wire to the fuel pump in the rear passenger side wheel well and replace the fuse, if it still blows then it's wiring or the relay, if not it may be a bad pump.
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Old February 28th, 2006, 08:27 PM
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Well a buddy and I determined that the fuel pump must be wired redundantly somewhere else. The pump gets power just fine with no 7.5A fuse installed. The presence of a fuse in the fuel pump slot is not necessary to run the engine. When one is installed, no problems either. It's just when I cut off the ignition that fuse snaps, probably from the redundant volts hitting it from 2 sides. I then either pull that fuse, or swap in a good one on the next crank.

I'll think I'll just cut my losses (.23 cents per fuse) and run the rig with no fuse installed in it's slot.

Whattya think?
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Old February 28th, 2006, 10:38 PM
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Personally, I would run a new wire to pump and be done with it. I don't like something hooked up that I don't know how/why. To hard to trouble shoot on the trail--I would rather do it in my drive. 2cents
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Old February 28th, 2006, 11:00 PM
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Yeah, running the fuel pump off some mystery wire (who knows whether it's fused or not) does not sound like a good thing. You should try tracing the wires to see where things go wrong. And as Chris mentioned, run a new wire from the fuseblock if you need to. One thing to keep in mind though is that there may be an inertia shut-off switch in between the fuse and the fuel pump (that's the way it is on my 110). I think it's a good idea to keep this switch operational (which it may not be with your mystery wire).
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Old March 1st, 2006, 12:09 PM
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Hmmm, wierd. I am not sure but I thought something else was also run off of the fuel pump fuse, or maybe thats the ECU fuse. Either way i would want to know where the fuel pum is getting it's power from.
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Old March 2nd, 2006, 07:55 PM
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Quote:
Originally Posted by Ryan Sakurada
Yeah, running the fuel pump off some mystery wire (who knows whether it's fused or not) does not sound like a good thing.
No, not at all. 'sound like some fool's been hacking up the wiring (I'm so glad I'm the original owner of mine).

Whatever you do, verify the line is properly fused. Otherwise you could have a bad fire one day.
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