Low-pressure pump driver test

[morayinc]

Hi all.
I have done a complete Fuel system service on my 2003 F225. I cleaned the fuel injectors, VST & filter, replaced the needle valve, F-filter (sacrificed-pretty clean), fuel filter & 10-micron racor.

My problem is the LP fuel pump is not cycling on. When I jumper the pump with 12V it keeps the fuel flowing great. I believe the LP pump driver has failed. Is there a test for the driver module? The book says to use a known good ECM. I don’t have one of those EXTRA. If anyone has a few ideas I would appreciate it!

[rodbolt17]

hook up a 12V meter or test lamp between the red and blue wires at the connector for the lift pump.
below 1200 RPM you should see about 12V for 10 seconds then off for 20 seconds.
the ground path is controled by the ECU via the driver and it cycles on/off at speeds below 1200 RPM.

[morayinc]

12V test=0

Rodbolt thanks for posting. I tested the ckt. the test shows 0Volts. even though the HP pump is humming away. I should have indicated the HP pump delivers the 40+lbs of pressure. Is there any other test to check that mod? morayinc

[rodbolt17]

then its possible the ECU or the fuel pump driver failed.
the red/yellow is hot anytine the key is on, the ground path is the blue/red.
the ground path is controled by the ECU via the driver.
power comes to the LP pump via the main relay then through a 5 amp fuse.
is the fuse blown?

[morayinc]

no, the fuse is not blown. But while inspecting, i found the fuses were all gunked up. Since it was late I cleaned them both-terminal and fuse. I will buy new fuses tomorrow. So I am back at the heart$ of the matter or leap of faith $200 DIY new driver. Any added thoughts?

[99yam40]

gunked up or corroded fuse holders or fuses can keep the voltage/ power from getting to where it needs to go. make sure you are getting the voltage through the connections after cleaned up or replaced before buying other parts.

[morayinc]

Those fuse holders are tight. I have done some hygiene, dental pick style. I could use some pointers to get them sparkly. I typically like to use Silicone or dielectric grease for these locations. When I get them clean I will add the barrier.

[rodbolt17]

with the key on do you have 12V between the red/yellow and a good engine ground?
if not then quit chasing drivers and ECU's.
if so then start backing towards the ECU to eliminate any wiring issues.
a wiring diagram would be a good thing about now.

[morayinc]

I will consult the wire diagram. I will chase the wires as suggested and reply with findings.

[99yam40]

with the key on do you have 12V between the red/yellow and a good engine ground?

Did it have the voltage after cleaning

[morayinc]

cleaned the fuse holders sprayed with silicone.

performed test, resulst:
red yellow-12V to good eng ground.
blue-red continuity between LP pump plug and driver plugs
solid black good eng ground continuity & in plug to ECM
black white: continuity from plug to ECM plug-
cannot verify continuity to good eng ground-Gave up to consult the forum.

Regarding black/white: I understand that this is the "switch" leg and is normally open. Turned the key and could not get the continuity to good eng ground. Does the ECM close the ckt to common engine ground? (that is a dumb question, what other ground it there?) I am not sure I on the right track for testing this ckt? I had to scratch around to get the eng ground bond on the other tests. Maybe I did not achieve the same bond on the b/w test? I will wait for the pros to confirm.

[morayinc]

The ECM plug was very clean no moisture noted. Thanks

[morayinc]

One more thing. I backed off the two ground bolts to the left of the ECM. wiggled the connectors to abraid the surfaces, then tightened them back up. These were very tight. Morayinc

[morayinc]

Rodbolt & 99yam40

I made the tests as specified. I am still not clear about the black/white wire to ECM. I get no voltage or ground continuity. How do I eliminate the driver as the failure, before purchase? Several posts indicate Ecm's rarely fail. Thanks!

[boatmangc]

if not then quit chasing drivers and ECU's.
if so then start backing towards the ECU to eliminate any wiring issues.
a wiring diagram would be a good thing about now.

Your answer is right here, do a continuity check from the connector at the fuel pump to the connector at the ECU