Go Back   Ford Truck Enthusiasts Forums > Newer Light Duty Trucks > 1997 - 2003 F150
Sign in using an external account
Register Forgot Password?


1997 - 2003 F150 1997-2003 F150, 1997-1999 F250LD, 7700 & 2004 F150 Heritage SPONSORED BY:

Welcome to Ford-Trucks Forums!
Welcome to Ford-Trucks.com.

You are currently viewing our forums as a guest, which gives you limited access to view most discussions and access our other features. By joining our community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join the Ford-Trucks Forums community today!





 
Reply
 
 
 
 
LinkBack Thread Tools Search this Thread
  #1  
Old 10-13-2011, 05:41 PM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Voltage required to start fuel pump?

Short story is that my 2000 f150 4.6L is starting intermittently (now its rarely) for the past week and turns out the fuel pump isn't always kicking on during startup. When I hear it kick on, the truck will start immediately. Odd thing is that the fuel pump and truck will always start with a battery jump starter. Checking voltage with a (slow) DVM at the fuel pump harness connector gives me:

Startup with battery:
12.05 for two seconds, then down to 6.83

Startup with jump starter on battery:
12.48 for two seconds, then down to 7.06

So, anyone know if this half volt difference might be the cause (bad ground? I dunno), or is the fuel pump not supposed to be that sensitive and it's going bad?

Things checked but no change:
New battery
Battery terminals thoroughly cleaned
All fuses checked, any fuses associated with fuel pump and PCM was replaced
Tried new relays for fuel pump and PCM, returned them
Anti-theft light doesn't flash
New fuel filter two months ago
Crankshaft connecter cleaned & dielectric greased
Fuel pump connector cleaned & dielectric greased

BTW, great forum, learned lots from you guys.
Reply With Quote
  #2  
Old 10-13-2011, 06:14 PM
Bluegrass 7 Bluegrass 7 is offline
Post Fiend
 
Join Date: Sep 2006
Posts: 5,016
Bluegrass 7 has a good reputation on FTE.Bluegrass 7 has a good reputation on FTE.
Could be a ground.
Have you eliminated the Crash sensor behind the passenger kick panel?
Half voltage is too low indicating there is to much resistance in the pump circuit feed or ground return.
Most pumps draw an average of about 7 amps.
At 12 volts cranking voltage the total circuit resistance would be close to 1/2 ohm.
How this is is 12v / 7a =.58 ohms.
If the circuit resistance rises for some reason, using the voltage you see as 6.83, the resistance would be .98 ohm or nearly double.
Taking the sum of the voltage drops for 12v - 6.83v would mean the circuit fault is dropping 5.17 volts. 6.83+5.17 = 12v.
This amount of drop is not tolerable in that circuit same at it would not be for lighting at any point on the truck.
The pump has to generate pressure at near 90 to 100 psi and won't do that on low voltage.
Keep looking. It's there some where.
Another item to keep in mind is if the return line is blocked, the pump is trying to pump against it and may draw excess current that will drop the voltage if there is any substanical resistance in the circuit.
Good luck.
Reply With Quote
  #3  
Old 10-13-2011, 06:30 PM
Bluegrass 7 Bluegrass 7 is offline
Post Fiend
 
Join Date: Sep 2006
Posts: 5,016
Bluegrass 7 has a good reputation on FTE.Bluegrass 7 has a good reputation on FTE.
Second part.
At key on to run, the PCM is powered up and closes a solid state switch to offer a ground to a relay for about 1 second.
This relay passes the fused power source to the pump circuit for a short time.
Under cranking load, the battery voltage 'drops' to about 12 volts.
Even at this point the pump puts out a high pressure to fully pressureize the fuel rails so the regulator can reduce it to the rated pressure range with some control by engine vacuum, after starting.
Reply With Quote
  #4  
Old 10-13-2011, 06:59 PM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Quote:
Originally Posted by Bluegrass 7 View Post
Half voltage is too low indicating there is to much resistance in the pump circuit feed or ground return.
Most pumps draw an average of about 7 amps.
At 12 volts cranking voltage the total circuit resistance would be close to 1/2 ohm.
How this is is 12v / 7a =.58 ohms.
If the circuit resistance rises for some reason, using the voltage you see as 6.83, the resistance would be .98 ohm or nearly double.
Taking the sum of the voltage drops for 12v - 6.83v would mean the circuit fault is dropping 5.17 volts. 6.83+5.17 = 12v.
This amount of drop is not tolerable in that circuit same at it would not be for lighting at any point on the truck.
This is all new to me so bare with me... I take it the voltage isn't supposed to drop at all after two seconds? Would this drop indicate something is "turning on" at that time causing the resistance and voltage drop? If not and say it's just a bad ground, wouldn't the resistance be immediate and always show 6.83 volts where I tested?

Quote:
Originally Posted by Bluegrass 7 View Post
Another item to keep in mind is if the return line is blocked, the pump is trying to pump against it and may draw excess current that will drop the voltage if there is any substanical resistance in the circuit.
Once the truck is started everything is normal at any speed, even quick starts and stops so I'm assuming there is no blockage.
Reply With Quote
  #5  
Old 10-13-2011, 10:52 PM
Bluegrass 7 Bluegrass 7 is offline
Post Fiend
 
Join Date: Sep 2006
Posts: 5,016
Bluegrass 7 has a good reputation on FTE.Bluegrass 7 has a good reputation on FTE.
To answer for once the truck is started.
Once the motor is started, the pump runs full time so the pressure gets up high enough.
Then at shutdown, the check valve in the pump holds the pressure for some amount of time before bleeding off, so a hot restart may not show to be a problem.
The proper way, though few ever do it, is to measure the pump flow rate or volume to determine if the pump has an issue.
Once you think a bit about it, pressure is not the only factor, but flow rate under that pressure has to be up with it.
The reason is the pump line pressure will rise if you squeeze off the return {but} the volume flow rate goes down. It's an inverse function.
Same as putting your finger over a water hose to increase the exit pressure. The amount of water coming out per unit of time is reduced.
For the fuel pump, the pump's capacity and line size determined by design is the sole control of pressure and volune at a specified design operating voltage.
Good luck.
Reply With Quote
  #6  
Old 10-14-2011, 12:34 PM
Bear 45/70's Avatar
Bear 45/70 Bear 45/70 is offline
Post Fiend
 
Join Date: Mar 2004
Location: Union, Washington
Posts: 6,056
Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.
Bad battery, replace it. The charger curing the problem told you that. Why does every one try to make this so hard.

During starting, if the battery drops below 10.5 volts, the battery is bad.
__________________
Bear 45/70

"Earth has its boundaries, but human stupidity is limitless."
Gustave Flaubert (1821-1880)
Reply With Quote
  #7  
Old 10-14-2011, 01:31 PM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Quote:
Originally Posted by Bear 45/70 View Post
Bad battery, replace it. The charger curing the problem told you that. Why does every one try to make this so hard.

During starting, if the battery drops below 10.5 volts, the battery is bad.
The battery has already been replaced even though it was tested by two different testers at two different auto stores, once mounted in the truck and once out.

The voltage test I noted wasn't at the battery, the test was at the harness connecter going to the fuel pump (black and pink wires).

I just tested voltage at the battery at startup about 20 times and this is what I got...

First 4 tries-
before turning key: 12.38v
turn key on (not start) and fuel pump kicks on for about two seconds: 12.21v
fuel pump stops priming: 12.25v

From the 5th - 14th(ish) try-
before turning key: 12.36v
turn key on and fuel pump doesnt kick on: 12.11v
after about two seconds then voltage is: 12.22v

About the 15th(ish) - 20th try:
before turning key: 12.30
turn key on and fuel pump kicks on for about two seconds: 12.16v
fuel pump stops priming: 12.20v

Looks like the fuel pump is trying to draw more power when it doesn't kick on. Perhaps fuel line blockage or bad pump? I may be able to try a fuel volume test today to help narrow things down.
Reply With Quote
  #8  
Old 10-14-2011, 01:57 PM
Bear 45/70's Avatar
Bear 45/70 Bear 45/70 is offline
Post Fiend
 
Join Date: Mar 2004
Location: Union, Washington
Posts: 6,056
Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.
A fully charged battery should read 12.8 volts before you do anything with it. 12.38 volts is way to low.
__________________
Bear 45/70

"Earth has its boundaries, but human stupidity is limitless."
Gustave Flaubert (1821-1880)
Reply With Quote
  #9  
Old 10-14-2011, 02:16 PM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Quote:
Originally Posted by Bear 45/70 View Post
A fully charged battery should read 12.8 volts before you do anything with it. 12.38 volts is way to low.
Alright, I'll see if I can borrow a battery or two. But if 12.38v volts is too low, I don't understand why the fuel pump would prime there AND at 12.30v but not in between.
Reply With Quote
  #10  
Old 10-14-2011, 06:22 PM
Bear 45/70's Avatar
Bear 45/70 Bear 45/70 is offline
Post Fiend
 
Join Date: Mar 2004
Location: Union, Washington
Posts: 6,056
Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.
The ignition switch does not control the pump voltage, the computer does. It turns on the pump to prime (pressure up) the system, the the pump shuts off. Once the engine starts the pump runs again. The voltage difference is negligible.
__________________
Bear 45/70

"Earth has its boundaries, but human stupidity is limitless."
Gustave Flaubert (1821-1880)
Reply With Quote
  #11  
Old 10-15-2011, 07:27 PM
rdw516 rdw516 is offline
Senior User
 
Join Date: Mar 2005
Location: Powhatan, Virginia
Posts: 113
rdw516 is starting off with a positive reputation.
I am having the same issues with my 2001 F150 Lariat 4.6l. I am trying to fugure this one out as well. If you figure it out let me know and I'll do the same. I am getting ready to replace the fuel pump. All relays have been replaced
Reply With Quote
  #12  
Old 10-15-2011, 10:37 PM
MisterCMK's Avatar
MisterCMK MisterCMK is offline
Avid Winter Hater
 
Join Date: Mar 2003
Location: Maple Grove, MN
Posts: 19,851
MisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputationMisterCMK has a superb reputation
Check the 12v feed from the fuel pump relay to the fuel pump. Have you tried a jumper wire from the battery directly to the fuel pump to see if it will solve the problem? You probably have a corroded connection or a bad wire.
__________________
Chris - Avid Winter Hater
2007 F-250 XLT 4x4 CC SB 6.0 PSD - ARP, IPR Gen2 EGR Delete, 4" turbo-back, no muffler, no cat, 6.4 banjo bolts, SCT X3, EA 270A Alt, coolant filter, air bags, Ranchos, etc.
1994 Mustang GT - HCI, Novi2k blower, MM suspension parts, etc
Hope & A Prayer Motorsports
Reply With Quote
  #13  
Old 10-16-2011, 01:03 AM
ford2go's Avatar
ford2go ford2go is offline
Posting Guru
 
Join Date: Apr 2003
Location: Frequently frozen MN
Posts: 2,476
ford2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud offord2go has much to be proud of
To clarify some stuff.

Your first note talked about a voltage drop after 2 seconds -- that's about the time that the fuel pump is shut off on startup. ( It runs for 2 seconds then the computer shuts it off until it senses that the engine has started).

So, you might have just been seeing your voltmeter drift downward.

Your battery voltage does seem a touch low - although not horribly so.
Full battery charge under controlled conditions is 12.65 v. However, temperature is a factor. Also, some DVMs aren't all that accurate.

You might try checking your charge voltage. Leave the meter on after the truck starts and see what it goes to. 13.8 v is pretty common, but it does vary. Could be that your alternator is not quite up to it.

Could also be worthwhile to make some jumper wires so that you can monitor battery voltage from the cab. Use some ring tongue terminals and try to sneak the wires into the cab with some kind of a connector in the cab so that you can get a reliable connection to your meter. Then you can see what's going on when it fails.

Good Luck,

hj
__________________
ford2go (hj)
No fords left except in my heart
Reply With Quote
  #14  
Old 10-16-2011, 01:45 AM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Man, good suggestions, I'll do some of these in the morning with what else I got planned, which is...

Remove the truck bed and rebuild the fuel pump assembly.

Don't scream at the computer, I know, I know...

Can't remember how many years ago it was rebuilt so might as well do the preventive maintenance even if it doesn't sound like the culprit. But, if it's seizing, that would explain the extra battery voltage drop at all the times the pump doesn't start, which is the main thing stuck in my head.

Also, it could be a blocked return as Bluegrass suggested. With the bed off I can more easily do a volume and pressure test on the entire return. Of course check all the electrical as well.

If all this doesn't cut it then perhaps Monday or Tuesday will be battery swap day. Hopefully an Expletive Touretts Day will not happen afterwards.
Reply With Quote
  #15  
Old 10-16-2011, 01:53 AM
fferd fferd is offline
New User
 
Join Date: Oct 2011
Posts: 9
fferd is starting off with a positive reputation.
Just to mention, the alternator was totally rebuilt about a year ago by a drag racing team's electrical and computer guru. Anythings possible but it's not high on the list at the moment.
Reply With Quote
Old 10-16-2011, 01:53 AM
 
 
 
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
6.0 solution now no start Tylor Reynolds 6.0L Power Stroke Diesel 17 04-25-2014 10:59 PM
Quirky start-up FlyingHigh85 Ranger & B-Series 9 10-31-2013 10:50 PM
Help request for a 7.3 no start Ogre39 1999 - 2003 7.3L Power Stroke Diesel 32 05-31-2013 07:53 AM
2000 Excursion 6.8L Fuel Pump Problem JDSIMPSON55 Excursion - King of SUVs 2 07-12-2012 10:47 PM
Electrical Glitches / Electrical / Electronic Diagnostics / Fixes Thread. gearloose1 6.0L Power Stroke Diesel 36 05-01-2010 02:28 PM


Go Back   Ford Truck Enthusiasts Forums > Newer Light Duty Trucks > 1997 - 2003 F150

Tags
2001, 98, check, escape, explorer, ford, fuel, fuelmpump, high, level, measure, pressure, pump, raptor, short, variable, voltage

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump



All times are GMT -5. The time now is 11:19 AM.


Powered by vBulletin® Version 3.8.7 AC1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Advertising - Terms of Use - Privacy Statement - Jobs
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.

vbulletin Admin Backup