Fuel Pump Fuse???

[plonghi]

On my 93 XLT. I was under the car doing some exhaust work. I finished that lowered the truck, got in started it up, sounded fine then stalled. It started right back up then stalled again. Did this 3 times. Itraced it back to the fuel pump fuse and it was popped. I replaced it, started right up and popped again. I tried a 30amp and that blew too. I hear the fuel pump turn on when I put in a new fuse and turn the switch on but it keeps popping. Any one seen this??

Help would be greatly appreciated

Patrick

 

[Opera House]

Try putting an old headlight in place of the fuse. !/4 inch spade pins fit into the fuse soclet and ease the wiring. The lamp will give an indication of when the circuit is shorting. Unfortunantly this circuit only turns on for a few seconds and testing will be difficult. I sugest you dig under the fuses and get to the fuel pump relay. Then jumper the two pins of the FP relay socket that are opposite each other and are 90 degrees opposite od each other. This will cause the pump to be powered all the time. The fuel pump will run with a lamp in series with it and dimly glow. A short makes it bright. You can wiggle wires around and unplug things to find the short. I suspect it is something involved with the work you just did.

 

[plonghi]

Someone told me when the pump gets tired the fuse blows does that make sense??

 

[Glacier991]

A failing pump COULD draw more juice than it should and the breaker would kick out if it exceeded the rated capacity. BUT! Opera House makes a good point (as usual)... whenever you do something, and something unexpected occurs thereafter, first look at what you did. A chafed wire to the pump could do this...might you have inadvertantly caught a wire in your work?

 

[TSTONE]

Check your jack points and the exhaust areas you serviced and make sure that you didn't pinch some wires. Sounds like something is shorting out.

 

[plonghi]

I will check work over tomorrow. Can I use a test light instead of an old headlight? And will I burn anything up when the circuit is completed?

 

[Opera House]

A headlight limits current to about 5A and protects the wiring. The lamp in series with a normal pump will still allow about 3A to operate the pump. You can also safely use 2 lamps in parallel for even more current. A test lamp limits current to about 1/4 amp. You would not be able to tell the difference between a normal and shorted pump. An initial test you could do is to unplug the external electrical connector at the tank. If the fuse doesn't blow or test lamp lamp doesn't light, then that kinda points to the pump. Of course, just moving the wiring a little could have fixed it for a moment.

 

[plonghi]

Checked over my work and all looked well. Will the headlight blow out at over 5 amps? And the fuse for the fuel pump is a mini fuse. Should I use maybe a paper clip to test with the headlight?

 

[Opera House]

I didn't think there were any mini fuses in the first gen. My test leads use an open U type screw terminal connector. I cut one f the sides off and this fits in the mini, regular and maxi sockets. Just don't use anything too thick that might stress the socket connector. The lamp can not burn out with normal 12V. A dead short makes it operate just like a headlight. Incandecent lamps have a unique property. Their "cold" resistance is 1/10 of the normal lit resistance.

 

[plonghi]

Ok heres the update. I unplugged what I believe is the fuel pump harness. It looks as if its located in the left frame rail under the drivers side door. After unplugged it still blew. So I think I may have narrowed it down to between those two points. Could a bad relay do this?? And you mentioned about having no mini fuses, this is a 9 of 92 would that be considered first generation??

Thanks again.

 

[DeRocha]

A first gen refers to the '91-'94 platform. I don't belive the fuel pump wiring is located under the drivers side... I would unplugg the wire connector from the fuel pump cut off (passenger side compartment under the glove box) right under the rug... This device is used like a circuit breaker to shut off power to the fuel pump if it senses an impact... Anyway just pull of the connector and see if it blows the fuse... Also don't use any fuse larger than 20A for the fuel pump circuit. The fuse is designed to protect the wiring not necessarily the pump...As such using a 30A fuse for the circuit now makes the wiring harness the weak link instead of the fuse and will cause it to overheat and fail... Your lucky you didn't cause a fire...

 

[plonghi]

WOW!!! Thanks, I didnt realize that extra 10 amps could do that. I will try unplugging the other switch tommorow. I wish I had stock in Bussman fuses their making a killing on me.

20 years of putzing with cars and this is the strangest thing ive come across
thanks for everyone help. My wife will be happy when she can get her car in the driveway again.

 

[DeRocha]

Here is a picture of the fuel pump cut off located under the glove box.

 

[plonghi]

Ok unplugged switch and the fuse did NOT blow. Is there a way to disconnect the fuel pump without dropping the tank ?

 

[DeRocha]

You should be able to locate the fuel pump wire harness above the tank near the rear. Dropping the spare tire will give you plenty of room to move around..

 

[DeRocha]

When you were doing your exhuast work did you use a torch? I believe the wire from the cut off switch runs in the passenger side floor channel (under the plastic foot moldings). When it reaches the end of the passenger rear door it travels across the floor to the driver's side......

 

[plonghi]

ok unplugged at fuel tank, new fuse, hit the switch, fuse did not blow. plugged in again hit the switch , blown fuse.

Do you think its the pump?

Advanced auto parts has one complete with sender for 130 dollars.

Anyone know how to do these??

 

[DeRocha]

I did mine a while back... You should read the maintenance link in my signature line. It covers this and many other topics... After reading through the material post back with any questions.. And yes I would recommend getting the whole unit as opposed to just the pump. Many times the sending unit is badly rusted and should be replaced (of course you won't know this until you've dropped the tank and looked at it first hand). I had to order my fuel pump and sending unit since no local auto parts store stocked it. It took 4 days to arrive at the parts store.

 

[plonghi]

any tricks on getting these fuel lines out? I bought the tool 3/8 and 5/16. It looks as if it slides into the metal flange backwards. I tried to spread open the tool and it did nothing. I jerked it so much that I snapped the line off at the top of the sender. Thank goodness it comes with the new pump. But Im still stuck with the broke off lines in the rubber lines.

 

[DeRocha]

Sorry about that I thought you had read the Fuel line tool use thead... It has lots of pics and good info on how to use the tool and why it is necessary...