Voltage to Drive a Fuel Pump - Taurus Car Club of America : Ford Taurus Forum
Register Home Forums Active Topics Topic Finder Photos Members List Search Today's Posts Mark Forums Read Auto EscrowAuto Loans
TaurusClub.com is the premier Ford Taurus Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools
Old 12-22-2012, 07:08 PM   #1 (permalink)
Junior Member
 
Member Number: 20425
Join Date: Jun 2009
Visit: My Garage
Posts: 32
Trader Score: 0 reviews
Rep Power: 0
qman has a little shameless behaviour in the past
Default Voltage to Drive a Fuel Pump

98 Taurus with 175 Kmi and original fuel pump.

Voltage at the pump harness is 6.8V. With pump plugged in this will spin the pump about one in 6 tries.

If I put 12V on the pump it spins every time.

Checked with a friend of a friend of a friend, who friend #2 says is a mechanic, and he says 6.5-7V is optimal voltage for driving a pump. Can anyone confirm this for me?

If the voltage is correct I'm gonna replace the pump (probably will anyway). If not I have more work to do.

Last edited by qman; 12-22-2012 at 07:23 PM.
qman is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 12-22-2012, 07:36 PM   #2 (permalink)
Member
 
Member Number: 17094
Join Date: Oct 2008
Location: Florida
Drives: 1999 Taurus SE Duratec
Visit: My Garage
Posts: 430
Trader Score: 0 reviews
Rep Power: 0
Scout1 has a little shameless behaviour in the past
Default

10.5 volts is the minimum voltage. You have a resistance in the 12 volt supply to the pump. Try swapping the relay for the pump with one of the others and see if it helps.
Scout1 is offline   Reply With Quote Quick reply to this message
Old 12-22-2012, 07:44 PM   #3 (permalink)
Junior Member
 
Member Number: 20425
Join Date: Jun 2009
Visit: My Garage
Posts: 32
Trader Score: 0 reviews
Rep Power: 0
qman has a little shameless behaviour in the past
Default

Swapped all three relays and voltage does not change a bit. 6.79V every time. If it were a problem in the wiring, I have no idea how I'd find that. The wires are bundled into a humongo trunk of wires.
qman is offline   Reply With Quote Quick reply to this message
Old 12-22-2012, 09:54 PM   #4 (permalink)
Crazy Devoted Member
 
Member Number: 5295
Join Date: May 2005
Location: Miramichi, New Brunswick
Drives: 2005 Taurus SE 3.0L Vulcan Bought with 111,432KM in October of 2012
Visit: My Garage
Posts: 5,749
Trader Score: 0 reviews
Rep Power: 34
the_intimidator_02 is a jewel in the rough
Default

You'll have to start looking over and check connectors, pins, etc for loose or corroded contacts. If that pans out, next you'll have to start and perform a voltage drop test and see where the voltage is being used up. What's your voltage at the inertia switch in the trunk?
__________________


Life is a hard teacher, it gives you the test before it teaches you the lesson.

The Human race is governed by it's own imagination.

Please don't steal, the government can't stand the competition.
the_intimidator_02 is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 12:16 AM   #5 (permalink)
Technical Advisor
 
behlinla's Avatar
 
Member Number: 14275
Join Date: Dec 2007
Location: Wisconsin
Chapter: Midwest
Drives: A blue car
Visit: My Garage
Posts: 7,524
Trader Score: 0 reviews
Rep Power: 81
behlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond repute
Default

Low voltage could also be the result of a bad ground if you were measuring both pins at the pump. If you can, provide a known good ground to one lead of your meter (e.g. run wire back to bat -), and test the voltage at the pump again. If it reads the full 12V that time, then you know you have a bad ground.

If you determine the problem is on the power wire, then you will have to open up the harnesses and probe the wire at various points going back towards the engine to find where the voltage drops.

Make sure you check your battery voltage and make sure it's good while you're doing the testing. It's easy for the battery to get drained with key on testing which might confuse you if you're trying to find a voltage drop that isn't there.

Again, a good battery should maintain 12.0V or more during key on testing, and the voltage at the pump shouldn't be more than about 0.5V lower than the battery voltage.
behlinla is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 12:20 AM   #6 (permalink)
Devoted Member
 
Member Number: 3136
Join Date: Jun 2004
Location: Omaha, nebraska
Chapter: Midwest
Drives: 1998 LX black Vulcan 1997 SE black Vulcan
Visit: My Garage
Posts: 1,745
Trader Score: 0 reviews
Rep Power: 25
soundu is on a distinguished road
Default

you need to back probe the 12volts with a known good ground to
find out where your losing voltage. If your probing around the relay
in the engine compartment, put the ground of the DVM on the negative
of the battery to assure a good ground.
Attached Thumbnails
Voltage to Drive a Fuel Pump-taurus-98-fuel-pump.gif   Voltage to Drive a Fuel Pump-taurus-98-fuel-relay.gif  
__________________
Bob Urz 1989 Vulcan wagon (wife crashed) 1990 Vulcan sedan (sold running) 1993 Vulcan sedan (wife crashed) 1993 Vulcan wagon (beat up like Battlestar Galactica, drove to junkyard on a sad day) 1997 Vulcan sedan (down with multiple coolant leaks), 1998 Vulcan sedan (rescued from being junked twice with broken brake lines and bad rack, currently resurrected)

If Spock drove a Taurus it would be a Vulcan

Last edited by soundu; 12-23-2012 at 10:10 PM.
soundu is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 10:07 AM   #7 (permalink)
Junior Member
 
Member Number: 20425
Join Date: Jun 2009
Visit: My Garage
Posts: 32
Trader Score: 0 reviews
Rep Power: 0
qman has a little shameless behaviour in the past
Default

Cleaned all grounds. Cleaned the ground coming out of the inertia switch, cleaned the ground coming straight off the battery.

I also took off the cover and cleaned them large spade terminals on the red battery cable that go into that relay box under the hood. Everything is nice and shiny now.

Still 6.78 volts.

So I then took apart the relay box under the hood and took voltage readings at the wires. The hot (red) wire going into the relay is 12V and with the relay installed and key on the voltage coming out of the relay is 6.78V, exactly what I'm reading at the pump. I also swapped all three of them identical relays and they all produce the same thng.

I'm starting to believe the friend of a friend of a friend. I can honestly say that I only understand the concept of what a relay is for. When I look at the image on the relay itself I swear one of them is a resistor. Would this account for the drop in voltage?

Comeon fellas . . . I need confirmation. I know what I have taken readings on. But I don't know what is right and what is not.

Last edited by qman; 12-23-2012 at 03:05 PM.
qman is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 04:57 PM   #8 (permalink)
Technical Advisor
 
behlinla's Avatar
 
Member Number: 14275
Join Date: Dec 2007
Location: Wisconsin
Chapter: Midwest
Drives: A blue car
Visit: My Garage
Posts: 7,524
Trader Score: 0 reviews
Rep Power: 81
behlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond reputebehlinla has a reputation beyond repute
Default

Okay, how are you testing this? Can you provide the wiring colors or the relay pin numbers? Key on or off? Be specific where you are putting each test lead.

There are two sides to a relay. One is the control side with the coil that produces the magnetic field. It gets 12V only when the key is on and the PCM relay is closed. When the PCM wants to run the fuel pump, it provides a ground on the light blue/orange wire, which will energize the magnetic field and close the relay. The coil will have a small resistance.

The other side is the power side, which is basically a switch. When it's open there is no continuity, and when the relay is closed the terminals should close with almost zero resistance. Power for this comes on the orange wire from fuse #10 (20A). When the relay closes, it provides power on the two dark green/yellow wires. One goes to the fuel pump, and the other goes to the PCM so it can sense when the pump is actually getting power.

Either way with a relay you should only have either 12V or no volts. So I'm not sure where the 6.78 volts is coming from. You should pull the relay and make sure you have zero volts at the pump. Otherwise you have a short into the circuit somewhere else.
behlinla is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 07:22 PM   #9 (permalink)
Junior Member
 
Member Number: 20425
Join Date: Jun 2009
Visit: My Garage
Posts: 32
Trader Score: 0 reviews
Rep Power: 0
qman has a little shameless behaviour in the past
Default

Thanks for the input. Not sure how a short would lead to 6.8V. Seems to me a short is zero.

The wiring is exactly as it is in the diagram above. Green/Yellow to the inertia switch and pink/black out of the switch to the pump.

The part you can't see in that diagram is the red (hot) wire into the relay and that the green/yellow come out of the relay to the inertia switch.

With key on I put a probe on the red wire coming out of the bottom of the relay (which is really power into the relay) and it reads the full 12V. On the two green/yellow wires coming out of the bottom of the relay socket, it reads 6.8V. It reads 6.8V into and out of the inertia switch, 6.8V into the pump and 6.8 into the pump with a jumper calbe providing ground straight to the battery's ground.

I actually removed that little black box that holds the relays (fuel pump/AC etc.) from the fiberglass cross member and pulled the plastic bottom off of it and put a probe on the spade connectors that the relay plugs in to. That is where the red wire shows 12.8V and the green/yellow show 6.8V.

What I'm telling you is that 12V goes into the relay and 6.8V comes out. The relay has a relay diagram on the side. It is not crystal clear what is what but I swear there is a resistance diagram on that picture.

If anyone out there has the time and drive, please do what I did. The relay box snaps right out and the bottom snaps right off of the box. You can put a multimeter on the bottom of the spade connectors and the ground of the multimeter to the battery with key on. Tell me what you get.

Please try to understand my dilema. I have a mechanic telling me that 6.8V is normal and you all telling me that it is not.

I hope this does not come across as me trying to be a prycque, but can anyone out there tell me that you "know for a fact" that it should be 12V or that "you think" it should be?

All I want to know is the facts.

Last edited by qman; 12-23-2012 at 07:27 PM.
qman is offline   Reply With Quote Quick reply to this message
Old 12-23-2012, 07:29 PM   #10 (permalink)
Devoted Member
 
Member Number: 3136
Join Date: Jun 2004
Location: Omaha, nebraska
Chapter: Midwest
Drives: 1998 LX black Vulcan 1997 SE black Vulcan
Visit: My Garage
Posts: 1,745
Trader Score: 0 reviews
Rep Power: 25
soundu is on a distinguished road
Default

Quote:
Originally Posted by qman View Post
Thanks for the input. Not sure how a short would lead to 6.8V. Seems to me a short is zero.

The wiring is exactly as it is in the diagram above. Green/Yellow to the inertia switch and pink/black out of the switch to the pump.

The part you can't see in that diagram is the red (hot) wire into the relay and that the green/yellow come out of the relay to the inertia switch.

With key on I put a probe on the red wire coming out of the bottom of the relay (which is really power into the relay) and it reads the full 12V. On the two green/yellow wires coming out of the bottom of the relay socket, it reads 6.8V. It reads 6.8V into and out of the inertia switch, 6.8V into the pump and 6.8 into the pump with a jumper calbe providing ground straight to the battery's ground.

I actually removed that little black box that holds the relays (fuel pump/AC etc.) from the fiberglass cross member and pulled the plastic bottom off of it and put a probe on the spade connectors that the relay plugs in to. That is where the red wire shows 12.8V and the green/yellow show 6.8V.

What I'm telling you is that 12V goes into the relay and 6.8V comes out. The relay has a relay diagram on the side. It is not crystal clear what is what but I swear there is a resistance diagram on that picture.

If anyone out there has the time and drive, please do what I did. The relay box snaps right out and the bottom snaps right off of the box. You can put a multimeter on the bottom of the spade connectors and the ground of the multimeter to the battery with key on. Tell me what you get.

Ok, were getting somewhere. What you have is a high resistance contact,
NOT a short. If your getting 6.8V out at the relay, theres you answer, almost.

Now what is it? two possibilities. One is the relay itself has bad contacts
internally, A new or swapped relay will tell you if thats it. The other is
bad contacts on the Socket going to the relay. Look down into the
socket where the relay plugs in. Does it look burnt or discolored?
if so, you found your answer.

If its a 98 or newer, you have separate relays, 97 or older, CCRM module.
__________________
Bob Urz 1989 Vulcan wagon (wife crashed) 1990 Vulcan sedan (sold running) 1993 Vulcan sedan (wife crashed) 1993 Vulcan wagon (beat up like Battlestar Galactica, drove to junkyard on a sad day) 1997 Vulcan sedan (down with multiple coolant leaks), 1998 Vulcan sedan (rescued from being junked twice with broken brake lines and bad rack, currently resurrected)

If Spock drove a Taurus it would be a Vulcan
soundu is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply


Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Taurus Car Club of America : Ford Taurus 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:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

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

Posting Rules
You may not post new threads
You may not 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 On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 04:13 PM.



Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO 3.3.2