Fuel Pump Voltage

[Coderedsaleen]

Can anyone help me out with this? I was only getting 11.5 volts to the FPDM from the CCRM for some reason. I have now ran a 8g wire from the battery to a relay controlled by the DG/YW from the CCRM. Now I have 13+ volts to the FPDM. When I check the volts going to the pumps from the FPDM it read 12.0 to 12.3 volts. Should the pumps be getting full 13+ volts all the time? Another thing that I noticed was that when I checked voltage again across the relay connections the voltage would drop and raise between 12.5 and 13.4 volts, would this be a indication that the alternator is not charging correctly?

Engine runs strong but hunts some what like a diesel, SCT data log says that the pumps are maxed in duty cycle and voltage is reading 12.2 or lower.

Background info: 2V to 4V conversion, complete OEM 2V wiring w/ modified wiring to the FPDM to match 03 Cobra (dual DG/YW dual wires from CCRM to FPDM and dual wires from the FPDM to the fuel pumps).

FPDM also heats up and shuts the pumps off and on. Any suggestions on if I should do the dual FPDM mod?

 

[04sleeper]

What kind of pumps are you running?

Have you pulled your tank to see if a hose popped off a pump? This could explain the 100% Duty Cycle.

 

[Coderedsaleen]

What kind of pumps are you running?

Have you pulled your tank to see if a hose popped off a pump? This could explain the 100% Duty Cycle.

I'm not sure what pumps are in it, the tank w/ pumps came with the engine so I'm assuming that it is the original Cobra pumps. I swapped the GT tank out for the Cobra tank. I did not open the tank before I installed it.

I know that the system does not hold pressure for long when I shut it off, is this normal. It is hard to start when I try to start it the next day.

Is there a chance that only one pump is running?

 

[04sleeper]

I'm not sure what pumps are in it, the tank w/ pumps came with the engine so I'm assuming that it is the original Cobra pumps. I swapped the GT tank out for the Cobra tank. I did not open the tank before I installed it.

I know that the system does not hold pressure for long when I shut it off, is this normal. It is hard to start when I try to start it the next day.

Is there a chance that only one pump is running?

It is very possible that only one pump is running. This is one of the reasons I prefer the Fore Hat over the stock hat. Each pump has it's own wiring so it can be easier to diagnose.

Sounds like you are going to have to pull the tank down anyway to check the pumps. That's where I would start.


It is tough to determine when you have made so many changes from the stock system.

Are you seeing max duty cycle at idle?

 

[Coderedsaleen]

It is very possible that only one pump is running. This is one of the reasons I prefer the Fore Hat over the stock hat. Each pump has it's own wiring so it can be easier to diagnose.

Sounds like you are going to have to pull the tank down anyway to check the pumps. That's where I would start.


It is tough to determine when you have made so many changes from the stock system.

Are you seeing max duty cycle at idle?

I'm probably going to pull the tank to see what is going on. I wish I would have checked all this out before I put it up in there. What a PIA!

I have not made that many changes to the stock system but live and learn from what to do and not do.

Yes I'm seeing max duty cycle at idle.

The voltage coming out of the FPDM is only 12 volts but coming in is 13.5 do you know if that is normal?

I just want to make sure that the voltage to run the pumps is correct before I pull the tank down. :shrug:

 

[jm@ReischePerf]

The voltage coming out of the FPDM is only 12 volts but coming in is 13.5 do you know if that is normal?

Yes, there should be a small voltage drop through the FPDM.

 

[Coderedsaleen]

Yes, there should be a small voltage drop through the FPDM.

Thanks! Just wanted to confirm before I take the tank out. I hope that the problem is in fact the pumps so it will be worth it.

Does anyone know what the out put voltage should be for the alternator? Mine ranges from 13.6 to 12.8 it cycles off and on. :shrug:

 

[Ontariomystic]

At idle the voltage going to the pumps should be closer to 4 volts. The fuel pump voltage table could way off.

But if you have a leak in the tank then the FRPS could be seeing low pressure and demanding alot more fuel.

 

[04sleeper]

At idle the voltage going to the pumps should be closer to 4 volts. The fuel pump voltage table could way off.

+1. Sounds like something is not working properly or the tune might be off.

A returnless system varies fuel pressure via the FRPS and the FPDM changes voltage based on inputs from it.

 

[bubblehead93]

This is a great discussion of how the ford returnless system works...

Ford Returnless System

Bottomline is this, the output of the FPDM to the pump is rapidly pulsed as the FPDM is "pulsing" the pump to ground to turn it on. It is not a steady DC signal so unless you have an oscilloscope you are going to see some sort of average voltage as a function of your multimeter's characteristics. So it should read lower than the input (especially if you include fpdm internal losses). The fpdm does not change the input voltage it just rapidly pulses the input voltage to the pump by shunting it to ground which in effect lowers the average voltage the pump sees.