Electrical help

[FormerNewMVGuy]

I am having some problems with my tank pump blowing fuse's! This is a new pump from TNJ Murry, John sent me a new pump,I installed it,It worked for about 20 miles and started blowing fuses's. I contact john murry and he sends me a new pump, I install it and it works for about 20 miles and is blowing fuse's Now TNJ Murry is telling me It is in my wiring harness
I dont see how that can be? I've checked all my grounds, my voltage seems okay, If it is blowing fuse's I would think it is between the pump and the fuse?
I am at a lose here and dont know which direction to go with this problem
Could somebody please give me a helping hand?

Thanks Scott

 

[alphadeltaromeo]

would be good to run some leads from a meter into your cab so that while driving, soldier A could watch it to see the fluctuation in voltage.

 

[FormerNewMVGuy]

How much fluctuation is allowable? Im a little stupid when it comes to 24 volt systems.

 

[JDToumanian]

If there's a problem with your wiring it would be between the fuse and the pump... a problem upstream wouldn't affect the fuse. Make sure nothing is touching a ground that shouldn't be... like the wires inside the metal fuse cover? Also, are you using the correct fuse? I think there was a PS Magazine article about using a 4-amp fuse instead of 2 or 3...

Is this new pump an exact mil replacement or a different after market type? Maybe it's motor simply uses more power and needs a little bigger fuse... Make absolutely sure though, I don't want you to burn up your truck because you took my crummy worth of advice!

Jon

 

[FormerNewMVGuy]

Well i bumped it up to a 4 amp fuse.I put the fuse in the pump runs fine, I drive the truck for a little while and the fuse blows! Ive looked it over a hundred times,just cant figure out what i'm missing

 

[doghead]

Are you using a 4 amp"slow-blow" fuse? Will the fuse blow if you just sit(stationary) and idle for 20 minutes?

 

[cranetruck]

You may have an intermittent short in the wiring after all, if it was the pump motor, the fuse would likely blow after a few minutes.
Check the connector housing and the wiring on the pump assembly, yes, you will have to pull the unit from the tank.
While you are at it, go over all the wiring to the tank, FWIW, the xm757 I'm currently "playing" with has three separate grounds to the tank, one for the pump, one for the level sending unit and on static ground to the tank itself. The tank wiring on the deuce leaves a lot to be desired.

 

[Cdub]

I would follow that hot lead from the fuel pump as far as you can until it reaches the power sorse. Look for any crimping or rubing on the wiring harness. Check all your conecting points where the harness goes through the cab and other sheet metal. I guess what I"m getting at is it sound like you have a short in the wire some were.

Also just for giggles....put a voltage meter on the hot side of the pump and make sure your not getting to much voltage. Clean all of your ground wire contacts.

C'dub

 

[DDoyle]

Also, when you pulled the pump was there any debris in the screen? The pump is magnetically coupled, so this should not be a factor, but it wouldn't hurt to be sure.

Has any part of the truck been rewired? Is any part of the wiring harness damaged?

If the size of conductor is reduced, the amp draw increases. That is, damaged wiring which reduce the number if strands has the effect of increasing the amp draw of the load on the circuit, which could cause the fuse to blow.

One other thing I'd try is turn the fuel pump on with the truck off and stationary - see if it will run an hour or so. If it does, the problem is probably a result of some type of vibration or movement from driving. If not, the problem is purely in the circuitry.

HTH,
David Doyle

 

[m-35tom]

any problem on the truck side of the pump would lower the volts and as a result lower the amps, so the problem has to be between the pump and the fuse. you will never know until you put an amp meter in the circuit and see how much the pump draws. if it is not an oem pump it could be much more than expected. there are many offshore parts being made and it is hard to tell sometimes. also it is not impossible to get 2 bad pumps in a row. check the amp draw.

 

[FormerNewMVGuy]

Thanks for the advice!I dont think the pumps are made here in the USA, they have metric nuts on the fuse holder, which leads me to belive that it is probably overseas junk! John murry tells me hes never had a problem with these pumps. I'm not a pro on electrical but know enough to get the job done. I think it is a high amp draw myself.Where can i buy a relatively cheap amp gauge?

 

[Blood_of_Tyrants]

You can get a digital multimeter from Wallyworld or Radio Shack for less than 20 bucks. Make sure it has a 10 Amp setting. If you get it from Radio Shack, it may have some alligator clips with it. Hook the red lead up to the source and the black lead up to the pump wire.

It sounds to me that the pump is working too hard. Maybe a problem with design or it just may be the wrong pump for the job.