Intermittent fuel pump short

[Mbam]

Recently my 2005 TJ (only 57,000 miles) died while driving. After a tow home found it had blown the fuel pump fuse. I measured the resistance of the terminal at the relay to ground and it looked like a short.

I dropped the tank so I could take the connector off the pump. As far as I can tell on this model the harness is one piece up to the relay. With the connector off the circuit was open as I would expect. Measured the resistance at the pump at less then 1 ohm. So I replaced the pump with what looks to be a genuine Bosch. Buttoned everything up and — it blew the fuse again. Resistance at relay - shorted.

Spent a day tracing the wire with my circuit tracer looking for the short and it appears good back to the pump.

Dropped the tank again, pulled the connector off the pump - short is gone. WTH? defective pump? Found that hard to believe so I bought a loose connector and hooked it up to a small 12v battery and connected it to the fuel pump (through a fuse just in case) and bingo - pump ran fine.

Hooked it back up and now it starts fine. Generally I'm pretty good with electric. but I don't trust it. As we all know an intermittent short is the worst.

Anyone ever run into something similar? Any hints?

On another note - after 20 years all the wiring and connectors are getting brittle. If I could find new harnesses I would replace them all as I am hoping for another 20 years out of it.

Thanks

 

[TJ4Jim]

Recently my 2005 TJ (only 57,000 miles) died while driving. After a tow home found it had blown the fuel pump fuse. I measured the resistance of the terminal at the relay to ground and it looked like a short.

I dropped the tank so I could take the connector off the pump. As far as I can tell on this model the harness is one piece up to the relay. With the connector off the circuit was open as I would expect. Measured the resistance at the pump at less then 1 ohm. So I replaced the pump with what looks to be a genuine Bosch. Buttoned everything up and — it blew the fuse again. Resistance at relay - shorted.

Spent a day tracing the wire with my circuit tracer looking for the short and it appears good back to the pump.

Dropped the tank again, pulled the connector off the pump - short is gone. WTH? defective pump? Found that hard to believe so I bought a loose connector and hooked it up to a small 12v battery and connected it to the fuel pump (through a fuse just in case) and bingo - pump ran fine.

Hooked it back up and now it starts fine. Generally I'm pretty good with electric. but I don't trust it. As we all know an intermittent short is the worst.

Anyone ever run into something similar? Any hints?

On another note - after 20 years all the wiring and connectors are getting brittle. If I could find new harnesses I would replace them all as I am hoping for another 20 years out of it.

Thanks

Welcome,

Open up the harness behind the vehicle side fuel pump plug and give it a look good see. Your in a salt enviroment like I was when I found internal corrosion immediately behind the plug that was fouling things up. Also if you need there are service manuals free to download in the resource section.

 

[Mbam]

Great idea, I will do that. I do have all the service manuals which have been very helpful.

If I could find new harnesses I would pull the body and change them all!

Thanks

 

[macleanflood]

Yeah I'd deloom the harness all the way back to the transfer case. It's all easily accessible. Then it runs along the passenger side of the transmission...might need to support the transmission and drop the skid for better access if you don't find the issue in the back 1/3.

-Mac