only 6.5 volts to the fuel pump - Ford Truck Enthusiasts Forums

Go Back  Ford Truck Enthusiasts Forums > Bronco > Bronco II
Reload this Page >

only 6.5 volts to the fuel pump

Notices
Bronco II Ford Bronco II

only 6.5 volts to the fuel pump

  #1  
Old 11-11-2011, 12:33 PM
hongkongrider
hongkongrider is offline
New User
Thread Starter
Join Date: Nov 2011
Posts: 10
hongkongrider is starting off with a positive reputation.
only 6.5 volts to the fuel pump

i have only 6.5 volts to the fuel pump. 6.5 volts to the inertia switch. my gut tells me its the ECM am i missing something?
 
  #2  
Old 11-11-2011, 06:19 PM
Lead Head
Lead Head is offline
Post Fiend
Join Date: Jul 2007
Location: Rhode Island
Posts: 7,837
Lead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to all
You haven't mentioned what year it is.

Next would be to check voltage at the fuel pump relay. If it's old enough, there should be two relays on the passenger fender side. One is ECU, one is Fuel Pump
 
  #3  
Old 11-12-2011, 12:14 PM
hongkongrider
hongkongrider is offline
New User
Thread Starter
Join Date: Nov 2011
Posts: 10
hongkongrider is starting off with a positive reputation.
it is a 1990 BII sorry for leaving that out. dont have too much experience in trouble shooting electrical so thanks for bearing with me on this.

just to let you know i have already put in a new relay and i still get 6.5 volts at pump. tried to check the voltage to the relay by removing the connector and checking the pins there. the drawing that i have in the manual indicates that red is the hot but i get no voltage there. checked all the others and now voltage so im doing something wrong. key is in the on position.

whats next?
 
  #4  
Old 11-12-2011, 01:10 PM
mrshorty
mrshorty is offline
Postmaster
Join Date: Dec 2001
Location: UT
Posts: 3,742
mrshorty is gaining momentum as a positive member of FTE.
6.5 V along the fuel pump circuit (post relay) is fairly normal when the relay is open. I don't know enough solid state electronics to explain it, but it is a "ghost" voltage from inside the PCM.

the drawing that i have in the manual indicates that red is the hot but i get no voltage there.
The red wire is one wire that should have 12 V KOEO. The red wire comes from the EEC relay, which should be closed whenever the key is on. If that red wire isn't showing power, go back to the EEC relay and make sure it has power there and that the EEC relay is closing. Not only is it essential for this wire to have power, but the PCM also has to have power, because the PCM is responsible for closing the fuel pump relay.

There should also be a wire (at the fuel pump relay) from the fuse/fusible link that has 12 V at all times.
 
  #5  
Old 11-12-2011, 01:18 PM
hongkongrider
hongkongrider is offline
New User
Thread Starter
Join Date: Nov 2011
Posts: 10
hongkongrider is starting off with a positive reputation.
there are 3 relays under the fuse box. i understand the fuel pump relay is the 3rd from the fire wall. which one is the ECC? based on what you said above i assume that the red wire into the ECC should have 12v as well?
 
  #6  
Old 11-12-2011, 11:43 PM
mrshorty
mrshorty is offline
Postmaster
Join Date: Dec 2001
Location: UT
Posts: 3,742
mrshorty is gaining momentum as a positive member of FTE.
which one is the ECC?
I'm not sure. Is there not a name for each relay in the power distribution box? Your wiring diagram should show the wiring to the EEC relay -- you may have to use that to identify which relay is the EEC relay.

based on what you said above i assume that the red wire into the ECC should have 12v as well?
Yes, and, assuming your '90 is the same as my '87 and '92, there are three pins assigned to that red wire at the PCM.
 
  #7  
Old 11-15-2011, 01:50 PM
hongkongrider
hongkongrider is offline
New User
Thread Starter
Join Date: Nov 2011
Posts: 10
hongkongrider is starting off with a positive reputation.
ok this is where i am. checked voltages through the ECC relay. how power to the blk/ylw there. changed the relay and then got power to the new fuel relay connector on the red wire with ing on. checked voltage at the fuel pump and got these readings.

when the key is turn to ing i get 12v that then drops to 7v.
with key in the starting mode i get 12v.

fuel pump does pump for approx 3 - 5 seconds. i assume that this is to pressurize the system. checked for fuel at the fuel rail at the pressure valve point and no fuel. held the pressure valve open while trying to start motor but still no fuel. is there something else inline that could be a blockage? ran it 3 times with no fuel coming.

what am i missing?
 
  #8  
Old 11-15-2011, 05:52 PM
Lead Head
Lead Head is offline
Post Fiend
Join Date: Jul 2007
Location: Rhode Island
Posts: 7,837
Lead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to allLead Head is a name known to all
There are two fuel pumps. One on the frame rail, and one in tank. If the in tank one dies, you'll get little to no fuel at the rail. The frame rail pump is located behind a small metal cover on the drivers side frame rail, up front. You'll see it, the fuel filter will be near it as well.

Disconnect the fuel line before the rail mounted pump (just pull the little plastic clip) and have someone cycle the key and see if fuel comes out of the tank.
 
  #9  
Old 11-15-2011, 10:08 PM
mrshorty
mrshorty is offline
Postmaster
Join Date: Dec 2001
Location: UT
Posts: 3,742
mrshorty is gaining momentum as a positive member of FTE.
The dual pump system was used up to '87 or '88. His is a '90, so it should have a single, high pressure, in tank pump. If he happens to have a "throw back" set up to the old 2 pump system, it would be important to know that both pumps are working.

If the pump is running, but no pressure is being generated:

1) Clogged filter
2) clogged pickup
3) other clogged line
4) bad pump

If you feel like you can do this carefully, disconnect the fuel filter, then run the pump briefly (you can use the fuel pump test lead in the self-test connector) and see if the pump is pumping anything to the filter.
 
  #10  
Old 11-16-2011, 02:14 PM
hongkongrider
hongkongrider is offline
New User
Thread Starter
Join Date: Nov 2011
Posts: 10
hongkongrider is starting off with a positive reputation.
i have a new fuel filter and a new pressure regulator. the only thing left is the fuel pump. when i bench test it, it seems to run fine but perhaps it isnt putting out the pressure necessary. is there a way to test it for out?
 
  #11  
Old 09-23-2018, 01:21 PM
John Finck
John Finck is offline
New User
Join Date: Sep 2018
Posts: 1
John Finck is starting off with a positive reputation.
fuse!

fuel pup went bad on my F150, changed pump but only 6.5 volts to it. turns out it blew the fuse when it locked up. new fuse, now she's running like a top again!
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
JDSIMPSON55
Excursion - King of SUVs
9
03-17-2017 04:11 PM
mytoolman
1948 - 1956 F1, F100 & Larger F-Series Trucks
8
12-06-2016 12:25 AM
voodoolord
1973 - 1979 F-100 & Larger F-Series Trucks
11
07-12-2015 02:26 AM
sammatt1
Excursion - King of SUVs
11
03-24-2014 01:00 AM
MV7
Fuel Injection, Carburetion & Fuel System
8
07-06-2013 12:54 PM


Thread Tools
Search this Thread
Quick Reply: only 6.5 volts to the fuel pump


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.