Fuel Pump Wiring Issue

[Coderedsaleen]

Took my 2001 Saleen, recently converted to 2003 Cobra engine, to the dyno to get tuned. I was told by the tuner that I was not getting proper voltage to run the fuel pumps so I was running lean. I have the Cobra tank and pumps installed. While he was doing the tune his computer said that the pumps were running at 50% duty cycle and he could not adjust it to make it push any more due to voltage.

The question is what should I do to correct this? I have taken a meter to the FPDM and I have 12 volts running to the pumps, but would this make the voltage split when it gets to the pumps to run 6 and 6? I check the the return signal wire and it reads 6 volts. Should I run dual FPDM to split the voltage or just run dual wires to the pump to increase the voltage?

I'm also running all stock wiring from 2001. I have done some research and the 2003 has a dual dark green/yellow wire spliced in with the same wire coming from the CCRM to the FPDM. Also there are dual wires spliced in with the wires that lead to the fuel pumps. These dual wires for each instance lead from one single wire, do these wires split the voltage then return it to a single wire to run the pumps? I wish I could get pics to better explain my situation.

 

[Coderedsaleen]

Anyone able to help?

 

[revmike]

Are you using a dc volt meter to read the voltage ? The fuel pumps are pulse width modulated (PWM). At 50% duty cycle they are on half the cycle period and off the other half. I THINK one wire out of the FPDM is just 12 volts dc (or battery voltage) to the fuel pumps. If you measure the voltage on this wire with a dc volt meter it will be 12 volts (or battery voltage) .Another wire out of the FPDM is the PWM wire. It is switching between ground and open to control the pumps at the requested duty cycle. If you measure the voltage on this wire with a dc voltmeter, at a 50% duty cycle, it will read about 6 volts. The Powertrain Control Module (PCM) tells the FPDM what duty cycle to run at. To get more fuel the PCM needs to tell the FPDM to run at a higher duty cycle( 80% , 90% ...). Maybe your PCM is missing some signal that lets it know it needs to turn up the fuel pumps.

 

[Coderedsaleen]

Are you using a dc volt meter to read the voltage ? The fuel pumps are pulse width modulated (PWM). At 50% duty cycle they are on half the cycle period and off the other half. I THINK one wire out of the FPDM is just 12 volts dc (or battery voltage) to the fuel pumps. If you measure the voltage on this wire with a dc volt meter it will be 12 volts (or battery voltage) .Another wire out of the FPDM is the PWM wire. It is switching between ground and open to control the pumps at the requested duty cycle. If you measure the voltage on this wire with a dc voltmeter, at a 50% duty cycle, it will read about 6 volts. The Powertrain Control Module (PCM) tells the FPDM what duty cycle to run at. To get more fuel the PCM needs to tell the FPDM to run at a higher duty cycle( 80% , 90% ...). Maybe your PCM is missing some signal that lets it know it needs to turn up the fuel pumps.

Yes I am using a DC multimeter, The DG/Y wire from the CCRM that connects to the PK/BK wire has 12 DC Volts, this powers the fuel pumps. The LB/PK from the FPDM has the 6 DC Volts, this is the signal wire. Not sure how to get the PCM to receive the right signal to push more power to the pumps. :bash:

 

[revmike]

On the 03 FPDM the dark green/yellow wire is the +12Vdc from the CCRM. The Black wire is ground. The brown/pink wire is +12Vdc to the fuel pumps. The red/black wire is the switched (PWM) wire connecting the FPDM to the fuel pumps. The white/red and light blue/orange wires go from the FPDM to the PCM. I think the last two wires are the ones that let the PCM control the duty cycle of the FPDM.

 

[Coderedsaleen]

On the 03 FPDM the dark green/yellow wire is the +12Vdc from the CCRM. The Black wire is ground. The brown/pink wire is +12Vdc to the fuel pumps. The red/black wire is the switched (PWM) wire connecting the FPDM to the fuel pumps. The white/red and light blue/orange wires go from the FPDM to the PCM. I think the last two wires are the ones that let the PCM control the duty cycle of the FPDM.

That is pretty much same set up for the 2001 GT wiring that I'm working with. The only differance is how the wires are ran. I have the DG/Y that runs to the fuel cutoff switch on one side then has the PK/BL on the other side running to the FPDM. All the other wires are the same. On the 03 Cobra the DG/YW runs to the FPDM. The fuel cutoff has a white wire on one side and then grounded. Other then that they are the same. Another exception that the 03 Cobra has and the GT doesn't is there are dual DG/YW from the CCRM and dual wires running to the fuel pumps. Both of these wires are spliced into single wires before and after they make connections into the the pumps and out of the CCRM then in the FPDM.

 

[Black306]

Depending on the PID selected, a value of .500 is actually equal to 100% duty cycle. It is more likely you are at 100% duty cycle than 50% even with a stock Cobra motor.

I'm still a little confused about how your pumps are wired. Are you using a stock Cobra hat? If not, are the pumps wired in series or parallel? In other words, is each pump wired to the positive and negative wires, or is one pump wired with the positive, other pump with the negative, and a jumper wire between the two?

 

[Coderedsaleen]

Depending on the PID selected, a value of .500 is actually equal to 100% duty cycle. It is more likely you are at 100% duty cycle than 50% even with a stock Cobra motor.

I'm still a little confused about how your pumps are wired. Are you using a stock Cobra hat? If not, are the pumps wired in series or parallel? In other words, is each pump wired to the positive and negative wires, or is one pump wired with the positive, other pump with the negative, and a jumper wire between the two?

I'm running the stock Cobra tank, hat, and fuel pumps. I have keep the orginal GT wiring harness. Would this create to much draw on the single wire that runs both pumps? :smmon:

 

[Black306]

I'm running the stock Cobra tank, hat, and fuel pumps. I have keep the orginal GT wiring harness. Would this create to much draw on the single wire that runs both pumps? :smmon:

Doubt it. A stock Cobra has only a single 14ga wire running to the top of the hat, and stock Cobras use the same FPDM as GTs. I don't know how a GT is wired, but I do know that the color of the wire powering the FPDM is a different color. Depending where the power is coming from may be causing your issue. Even then, I doubt that is your problem. You can try to run power straight from the battery to the FPDM using the FPDM's current power wire as a signal to a relay. That kind of wiring is shown in my dual FPDM conversion.

Is the Cobra engine stock?

 

[Coderedsaleen]

Doubt it. A stock Cobra has only a single 14ga wire running to the top of the hat, and stock Cobras use the same FPDM as GTs. I don't know how a GT is wired, but I do know that the color of the wire powering the FPDM is a different color. Depending where the power is coming from may be causing your issue. Even then, I doubt that is your problem. You can try to run power straight from the battery to the FPDM using the FPDM's current power wire as a signal to a relay. That kind of wiring is shown in my dual FPDM conversion.

Is the Cobra engine stock?

The Cobra engine is basicly stock, I have a Steg blower, smallest pulley that you can put on it and a CAI. Running all the stock GT wiring.