In-Tank Fuel Pump Electrics

[Akicita]

My in-tank fuel pump is not working. A 20 (twenty) Amp fuse blew!! I need help from someone who understands electrics better than I do.

I followed the procedure described on page 2-219 in TM 9-2320-361-20 but need help interpreting the results.

I removed plug 654 from the socket on the tank top plate and read the following from the three terminals on the plate:

With the truck not running and the accessory switch OFF:
-31 VDC + 0 VDC + 0 VDC
With the truck not running and the accessory switch ON:
-55 VDC + -55 VDC + -55VDC
There were slight differences but I rounded all readings off to -55 VDC.

Then I checked the plug I had removed and read
0 VDC + 90-something + 90-something VDC
The meter kept climbing. I stopped when it had surpassed 90 VDC.

Why don’t I get a reading in the neighborhood of 24 VDC ?
What does a negative reading (minus sign in front) mean ?

I have not changed anything on the batteries since I bought this truck a year and a half ago, and it runs fine even with that pump inoperable but it takes longer and longer to get it started.

 

[emmado22]

55 plus volts? You got big problems.... I dont know what they are, but thats not good. 24-28 is the max Volts you should see out of the truck anywhere in it.

 

[John S-B]

Kind of obvious, but are you sure you're using the right setting/scale on your meter? Is it calibrated right? Try it on something you know is working right. I don't know how you could get much more than 24-28 volts without something frying.

 

[KsM715]

What type of meter are you using? Is it on the right settings?

Like emmando22 said, if your getting 55Volts and up, you got some serious problems.

 

[gimpyrobb]

Possibly a bad voltage regulator. Pull your alt and have it tested.

 

[doghead]

Or just measure your batteries with the truck NOT running, then running and compare.

 

[gimpyrobb]

That too.

 

[doghead]

I better me more specific, for the single cell members.

Measure the battery VOLTAGE (not total weight or dimensions), but you could measure specific gravity of the acid...

 

[phil2968]

Or just measure your batteries with the truck NOT running, then running and compare.

What size should they be?

Just being funny!

 

[doghead]

It's a comparison test Phil, just measure however/whatever you can. The results should be "MORE" when running.

 

[Boatcarpenter]

The 55 Volt reading is 2 x 27.5 volts, which would be a good reading for your batteries.
As others have said, check the range or settings on your meter.
BC

 

[emmado22]

These are 2 each 12V batteries (24V total), not 2 each 24V (48V total)

 

[jasonjc]

All you need to know is that you have voltage to the plug same as as the batt. I.E. use a test light (24volt). Plug one end into each hole in the plug.


But you said you blow a 20 amp fusse (witch is 10X what should be in there). That means you have power. Pull your pump and check to make sure it not pluged or fozen up.

 

[bullfrog1234]

check your grounding points for the pump. if the pump is shot or short, will result most times in a popped fuse.

 

[Akicita]

Thanks for all your comments and ideas.

The meter works fine. I had just tested another car battery before I got to the truck and the car battery read 12.7 V, which is just about perfect.

I used that same meter on the plug on the truck.

My truck came with two 12 V car batteries when I bought it about a year and a half ago. Those batteries were new at the time. I looked for corrosion and bad ends and what have you but everything looks good. So, with two 12 V batteries, the total voltage should be in the range of 24 to 28. As someone pointed out, I got twice that much.

New question: Why does this never happen when I buy a lottery ticket ?