No fuel again

bluejeep

bluejeep

TJ Enthusiast
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About 10 months ago I lost fuel to the motor. Installed new Bosch replacement fuel pump, and had to also install a new fuse for the fuel pump. Noticed after I replaced the pump that the fuse was blown

Today I lost fuel pressure again - noticed right away the fuse was blown.

Inspected wiring and did not find any obvious shorts.
Installed a new fuel pump (not Bosch this time). Before mounting the tank back up, I turned the key w/o starting and verified that the fuse did not blow. It did not. So I finished putting the tank back into place.

The vehicle started, ran long enuf to back out of the garage, then quit. Fuel Pump fuse was blown.

So I either (miraculously) got a bad fuel pump, or I did not fix a short I previously missed (but then why did it run for a minute?), or there is something that is causing fuel pumps to short and it takes only a minute before the fuse blows.

Any clues what to check?

Does this sound right ? To check the voltage to the fuel pump I believe I need to drop the tank to unplug the connector on top of the fuel pump, then use a multi-meter to probe the supply voltage with 1 probe, and ground with the other.

Thanks in advance
 
Related question.

Is there someway to check the integrity of the fuel pump, maybe while the tank is dropped and unplugged, or even while it is removed from the tank?
 
thinking wiring issue now for sure. Replaced the fuse, it started and ran for a few minutes, I backed out of the garage, fine, put it in first, it died. Fuse blown

replaced fuse, tried starting, just blew the fuse.

So I think the pump is fine, it's just a short somewhere that I need to find. Not great with electrical but I will muddle thru
 
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Won't get to look into this until next week, so if anyone discovered a spot where their wiring insulation was damaged, exposing the wire to potential of shorting out, let me know where it was on the vehicle, especially as related to the wiring for the fuel pump. TIA
 
bluejeep said:
Won't get to look into this until next week, so if anyone discovered a spot where their wiring insulation was damaged, exposing the wire to potential of shorting out, let me know where it was on the vehicle, especially as related to the wiring for the fuel pump. TIA
Click to expand...
Mine was damaged near the tank. The harness was catching on the track bar bolt.

20210307_213007.jpg
 
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at long last, an update - and resolution.

First I printed out the wiring diagrams from the factory service manual, learning the symbols for wire colors, splices, grounds, etc. Located the fuel pump and associated wires coming out of it. Looked into where those wires ran on their way from the fuel pump to the fuse block or computer. Now I had a good idea of what I was looking for, where to look, and where to not bother looking.

Dropped the tank and checked the wiring connection at the top of the fuel pump - looked fine. Checked along the line going forward, didn't notice any damage to the loom until after the wire bundle crossed over the top of the transmission. On the passenger side, the wire loom had been melted by exposure to hot air caused by a leak in the exhaust just before the rear cat. Thought I found the electrical problem until I failed to notice any damage to any of the wire insulation, just a melted loom. Decided to remove the cover around the stick shift so I could see this spot from a better / different angle. Glad I did that because it allowed me to inspect the wires better (found no issues) and re-bundle the wires in new loom, surrounded by heat wrap left over from wrapping the exhaust, and route them further from the heat (exhaust was also repaired.)

The reason I was especially glad I had removed that cover to look in from the top is because I spotted an area of damage on the drivers side of the transmission, where the wire bundle had shifted close to the front driveshaft CV joint. There it was, the shine of bare copper. Repaired, re-routed, and tomorrow I will replace everything I had removed to get to this point (fuel tank, tranny cover plate).

I'm confident this will fix the problem of the fuel pump fuse blowing, and realized this was most likely the issue with the previous fuel pump issue (but then why did it work fine for months after I replaced the fuel pump back then, hmmm?).

I also am reasonably certain I may have caused this wire rubbing on the front driveshaft issue by inadvertently dislodging that wire bundle forward when I spliced in the 'yellow box' to correct the speedometer after re-gearing.

Whatever doesn't kill me makes me stronger I guess - onward we go
 
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