7 volts to fuel pump? - Ford Mustang Forum

LinkBack Thread Tools
post #1 of 5 (permalink) Old 10-21-2006 Thread Starter
grivlet's Avatar
Joined: Oct 2006
Location: Jackson
Posts: 36
Question 7 volts to fuel pump?

i have a 1991 mustang LX 5.0 hatch... i got the tank dropped out of the car to replace the fuel pump... hooked it up to test... and nothing! checked the fueses - they were all good. then i whipped out the voltmeter and checked the battery for a baseline - 12 volts there. checked a random fuse for power. got 12 volts at the fusebox. then i checked the connection that goes from the car to the fuel sending unit and got 7 volts. where in the world did my five volts go? is it mabye my fuel pump relay? is that under the passenger seat? and (dont make fun) could i just wire this up to a switch on the dash? i've spent hours and hours and cant figure out why im only getting 7 volts to the pump. if i could only get that magical 12 volts then im positive the car will start. someone please help before i give up hope!

1965 mustang coupe
all original
200ci I-6
grivlet is offline  
Sponsored Links
post #2 of 5 (permalink) Old 10-21-2006
GT Member
V6 Member
5.0L Member
StalkerStang's Avatar
Joined: Apr 2002
Location: Surprise
Posts: 2,137
Send a message via Yahoo to StalkerStang
Do you have a diagram for the fuel pump circuit?

If you are on the correct wire, and your checking available voltage to the pump, make sure you are doing it with the fuel pump in its running position, or the reading won't be accurate. In other words when you check voltage there, kick the key over (when it primes the fuel system) and then check your reading.

Jesse Berger
90 LX, Previous 4 cyl.
408W In the Works
TW FAC's, Jay Allen cam, Super Victor

2001 V6 5 Speed Daily Driver
Windstar Intake, Dual Exhuast, CAI, Headers
Best ET: 15.44@91 mph (on 18's)
StalkerStang is offline  
post #3 of 5 (permalink) Old 10-21-2006
MACH I Member
5.0L Member
FoxChassis's Avatar
Joined: Jul 2003
Location: NOYB
Posts: 2,779
The title of this topic says "fuel pump", then in the message body you said you tested "the fuel sending unit" and got 7v, and then you said you're getting only 7v at the "pump". So are you checking voltage at the sending unit or at the pump?

1979-1993 Fox Capri and Mustang VIN Decoder: foxchassis.com

Wanted (Dead or Alive): VINs, Vehicle Certification Labels, Buck Tags, Build Sheets, Window Stickers, Owner Cards, Warranty Tags, History 999 Reports, Invoices, Axle Tags
FoxChassis is offline  
post #4 of 5 (permalink) Old 10-22-2006
rustang6947's Avatar
Joined: May 2004
Location: Torbay
Posts: 59
Are you checking the voltage on the pink-black wire (my stang is a 88 but wire should be the same) That wire comes right from the fuel pump relay. To make it easier to check turn the key to run and ground the single wire plug at the computer test conector. This will close the fuel pump relay and supply a constant 12V to the pump. Check voltage at conector first with pump unpluged and using a good ground. if you don't have 12V there remove the relay and install a jumper wire from the pink-black wire to the orange -lite blue wire, if you get 12V then replace the relay. If you still don't start checking for a bad wire.

To alcohol, The cause of and answer to all of life's problems.
rustang6947 is offline  
post #5 of 5 (permalink) Old 11-17-2006 Thread Starter
grivlet's Avatar
Joined: Oct 2006
Location: Jackson
Posts: 36
well thanks for all the input... apparently the car we got had been sitting outside for some time with the window part way down (this was apparent because the carpet was still damp under the seat) and we found that we simply needed a new relay... put that in and the car fired right up... idled and runs fantastic... i think i got my 1000 dollars worth

1965 mustang coupe
all original
200ci I-6
grivlet is offline  
Sponsored Links
Closed Thread

Quick Reply

Register Now

In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

For the best viewing experience please update your browser to Google Chrome