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pump fuse blows then rough idle


mulwyk
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The car: '89 Pathfinder, 5 speed, 4X4, 160,000 miles, VG30i

 

The situation: we leave our Pathfinder at the farm during the summers...it runs very few miles, just back and forth to the pasture. Then in the Fall we bring her back to town where she is our primary car over the winter. We been doing that for 20 years with no problems. But this year we got about 200 miles out when the old girl just stopped running!

 

Took awhile to find the problem: a blown fuel pump fuse. We replaced the fuse and it started right up, ran about two minutes at high idle (1500rpm), then went into a very rough surging idle...2000rpm, 1000rpm, 2000, 1000.....etc.

 

We checked the ECU codes...it's flashing "55, no problem"

 

Any idea what might be wrong?

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Stale gas? Clogged fuel filter?

Could be. As part of our winter prep, we drain the gas out of the tractor, mower, generator, etc. and put that old gas in the Pathfinder. So the gas was about 6 months old, and maybe had some old-tractor-gas-tank crud in it.

 

Would a clogged fuel filter cause the fuel pump fuse to blow?

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Not necessarily. It may increase current draw of the fuel pump since it has to work harder to pump, but a clogged or highly restricted fuel filter usually manifests issues when trying to reach higher RPMs, not starting and idling. But you never know, and fuel filters are relatively cheap anyway.

 

I wonder if Stabil Marine will help 'freshen' the gas at all? It may at least deal with any water build up.

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Your issue could be the electrical connections on top of the sending unit at the fuel tank. They get corroded over the years, and start to short out. I had to replace the sending unit on both of my Pathfinders because of this issue. There should be an access panel for it under the carpet in the cargo area.

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Well, I replaced the fuel filter. (Thank you, Towncivilian) The old girl started right up, ran about 1500 rpm for a minute or so, then settled into a 800 rpm purr. She seems to be running perfect now.

 

That's all that was wrong!? A clogged filter??

 

Next, I'll check the fuel pump connections and put some StabiI in the tank, but I feel like I should do something more. Replace the fuel pump? Clean out the tank?

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Well, lets put it this way, when was the last time you changed the fuel filter? That it might have been clogged after swapping old gas for years wouldn't surprise me.

 

Pay heed to what Simon said though, it is a common problem as these rigs age but thankfully it is not difficult to access or repair. That was my first guess when I read the description of your problem, intermittent short...

 

B

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Well, lets put it this way, when was the last time you changed the fuel filter? That it might have been clogged after swapping old gas for years wouldn't surprise me.

 

Pay heed to what Simon said though, it is a common problem as these rigs age but thankfully it is not difficult to access or repair. That was my first guess when I read the description of your problem, intermittent short...

 

B

Last fuel filter change...I don't remember...maybe five years ago? Anyway, I'm sure it's long overdue.

 

I should note that when the fuse blew, we had been running in heavy rain for over an hour. The top of tank/fuel pump area may have been awash at the time.

 

I found the fuel pump (It WAS easy to access once I got past the carpet and those cargo hooks). The top of the pump was like a little forest of rust flakes which I cleaned up with a tooth brush and a vacuum cleaner. The wires look good now and are standing proud, so I've decided to wait and see what happens before replacing the pump.

 

(The wife was real sweet about my unilateral "wait and see" decision, She went out and bought me a spare fuel filter and a little packet of 10 amp fuses,)

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