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As far as wiring in dual fuel pumps in the tank, does it matter where the wires to the second fuel pump is spliced from?

This is on a 98 Mark VIII.
 

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Have you removed the FPCM in the trunk? The Gen II Mark VIII's vary the voltage to the pump to vary the speed, and I'm not sure if the FPCM could handle the extra current load from a second pump.

Just my .02. :thumbsup:
 

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You'll probably end up having to do a setup much like what the cobra folks have to do.. dual FPDMs. I helped RobertP with this on a car.. he'll probably remember more about doing this than I would. Here's a link to a dual FPDM article. Keep in mind this applies to the cobra fuel system, but the principles should be the same. You'll have to make friendly with a wiring diagram to apply this to the mark viii.

Edit: wow.. forgot the link
http://www.innovativesitedesign.com/03cobratech/gt40pumpupgrade.html
 

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Yes you need dual fpdm there is write ups how to wire it on and 03 04 cobra so basically each fpdm controls each pump cause otherwise u will over load the fpdm unless u buy and upgraded on gem like lethal performance that can handle more amps. Not sure hot this would work on a mark 8

Robert
 

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Geez a returnless fuel system with a FPDM is nothing like a Mark8. Quit steering the guy wrong. It's a simple 2 speed fuel pump on a return system.
 

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Geez a returnless fuel system with a FPDM is nothing like a Mark8. Quit steering the guy wrong. It's a simple 2 speed fuel pump on a return system.
You know not of what you speak....

The Gen II's have a FPDM (my mistake, I called it a FPCM) mounted in the trunk. I just replaced the pump in my tank thinking I had a failed pump. In actuality it was the FPDM which does control the duty cycle.

http://forums.tccoa.com/showthread.php?p=1269155

Fuel Pump Driver Module Applications

The Fuel Pump (FP) signal is a duty cycle command sent from the Powertrain Control Module (PCM) to the Fuel Pump Driver Module (FPDM) (Table 5). The FPDM uses the FP command to operate the fuel pump at the speed requested by the PCM or to turn the pump off.

FP Duty Cycle Command: 0 - 5%
FPDM Actions: PCM will not output this duty cycle.
PCM Status: Invalid FP duty cycle. FPDM will command fuel pump full on. FPDM will send 25% duty cycle signal on the Fuel Pump Monitor (FPM) circuit.

FP Duty Cycle Command: 5 - 51%
FPDM Actions: Normal operation
PCM Status: FPDM will operate the fuel pump at the speed requested. ("FP duty cycle" x 2 = pump speed % of full on (for example FP duty cycle = 42%. 42x2=84. Pump is run at 84% of full on.)). FPDM will send 50% duty cycle signal on FPM circuit.

FP Duty Cycle Command: 51 - 67.5%
FPDM Actions: PCM will not output this duty cycle.
PCM Status: Invalid FP duty cycle. FPDM will command fuel pump full on. FPDM will send 25% duty cycle signal on the Fuel Pump Monitor (FPM) circuit.

FP Duty Cycle Command: 67.5 - 82. 5%
FPDM Actions: To request the fuel pump off, the PCM will output a 75% duty cycle.
PCM Status: Valid fuel pump off command from PCM. FPDM will not operate the fuel pump. FPDM will send a 50% duty cycle signal on the FPM circuit.

FP Duty Cycle Command: 82.5 - 100%
FPDM Actions: PCM will not output this duty cycle.
PCM Status: Invalid FP duty cycle. FPDM will command fuel pump full on. FPDM will send 25% duty cycle signal on the FPM circuit.
 

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Well I can see why it would need to be PWM for returnless, but if its a return system I just dont understand the function of the FPCM. Also I remember reading in the SHM book about the dual fuel pump setup on 03+ cobras, couldnt you just use whatever control module and pumps an 03+ Cobra uses? If you are installing dual fuel pumps in a car with a return system and are worried about burning things up, why cant both pumps be ran with relays? In a return system, more fuel coming back will only "cool" the pumps even more. Just some ideas from my side of the table.
 

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Well I can see why it would need to be PWM for returnless, but if its a return system I just don’t understand the function of the FPCM. Also I remember reading in the SHM book about the dual fuel pump setup on 03+ cobras, couldn’t you just use whatever control module and pumps an 03+ Cobra uses? If you are installing dual fuel pumps in a car with a return system and are worried about burning things up, why can’t both pumps be ran with relays? In a return system, more fuel coming back will only "cool" the pumps even more. Just some ideas from my side of the table.
Silly boy, you're trying to apply logic to Ford engineers. :D :tongue:

I'm sure you can get it to work without the FPDM, but without that feedback from the FPDM, the PCM will throw a CE and not know what the fuel system is doing. I know for a fact that if you bypass the FPDM it will throw a CE, but the car will run/drive (but I don't know about long term).

I would assume that could be tuned out with a custom tune.

I agree, I couldn't see any reason for the FPDM either.... especially after dropping the tank and replacing the pump. The FPDM took all of about 15 minutes to replace vs. the hours for the pump.... :redmad:
 

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Discussion Starter #10
You know not of what you speak....

The Gen II's have a FPDM (my mistake, I called it a FPCM) mounted in the trunk. I just replaced the pump in my tank thinking I had a failed pump. In actuality it was the FPDM which does control the duty cycle.

http://forums.tccoa.com/showthread.php?p=1269155

Thanks for the info! I can't seem to find my CD manual for the car. I won't be adding the 2nd fuel pump until this winter, but I'd like to get all the info I can now.

From that link you sent, would the best way to measure the voltage going to the fuel pump be to measure pins 3 and 10 from the FPDM?
 

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I'm not sure if it is a voltage or if it uses PWM, so I have no clue what the signal should be.

Have you looked at the fuel pump "assembly" in the tank? It is VERY different from the early FN10's and the MN12's. When I had my tank out, I looked to see if there was a way to do dual fuel pumps and it really didn't look possible. I purchased a higher output pump supposedly specifically for the Gen II’s and it didn't fit properly, nor did the high output pump that was in my MN12. So I went with a new OEM replacement. :(

http://www.rockauto.com/catalog/moreinfo.php?pk=296750

The pump is inside the “bucket”, which fits into a socket in the tank…

And the fuel level sensor snaps to the side of the bucket. So nothing is simple... :bawling:
 

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I guess you learn something new every day! I had no idea those engineers were making things new & improved and I didnt even know about it, lol ;)
 

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From that link you sent, would the best way to measure the voltage going to the fuel pump be to measure pins 3 and 10 from the FPDM?
If it's PWM driven, you will need a "True-RMS" voltage meter to read the voltage correctly; the duty cycle (ratio of amount of time on to time off) will vary, but the voltage is either ~12V or off, changing very fast.

A standard meter won't read that very well; possibly well enough to tell whether 25% or 50%, tho.
 

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A good Oscilloscope with memory is about the only way to really monitor/record a varying PWM signal (IMHO).

True RMS is good if the PWM is steady state, but once it starts to vary it is tough to get a good reading.

One of these days I'll break down and buy a good multi-channel O-scope. :D
 

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Discussion Starter #15
I have a Ford GT fuel pump and am going lean above 5000 rpms. The way I have the pump in the tank, it is not being starved. Pretty much the only function of the "cup" is to hold the fuel float sensor. I know the 60# injectors are not maxed out. So it's either the fuel lines or the fuel pump.

I measured the voltage going to the pump from the fpdm. It was about 8 Vdc at idle and 12.4 Vdc at WOT. I was just reading DC so I was unable to tell anything about the duty cycle. But at least it looks like the peak voltage is alright.

Is there any way to tell if the fpdm is going bad? I wonder because is seems as though my dyno runs yesterday were erratic. One run it would hold fuel pressure up to almost 5500 rpm, then just taper off. Another run it would completely drop off around 4500.
 

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You know not of what you speak....

The Gen II's have a FPDM (my mistake, I called it a FPCM) mounted in the trunk. I just replaced the pump in my tank thinking I had a failed pump. In actuality it was the FPDM which does control the duty cycle.

http://forums.tccoa.com/showthread.php?p=1269155
No actually, you know not of what you speak. You can make this claim all you want, but reality is that it is not in the calibration. The pump switches to high at 4000 rpm, and back to low at 3800. Two speeds, that's it. See I'd rather look at the cal and see what is actually in there, rather than taking the word of some dealership level manual which quite often contain incorrect information.
 

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No actually, you know not of what you speak. You can make this claim all you want, but reality is that it is not in the calibration. The pump switches to high at 4000 rpm, and back to low at 3800. Two speeds, that's it. See I'd rather look at the cal and see what is actually in there, rather than taking the word of some dealership level manual which quite often contain incorrect information.
Well....

My '98 Mark VIII BTC0 PCM specifies a type 2, modulated fuel pump, that uses a FPDM, not simply a two-speed.
 

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Well....

My '98 Mark VIII BTC0 PCM specifies a type 2, modulated fuel pump, that uses a FPDM, not simply a two-speed.

And that is exactly the catch code I looked up, which switches to high at 4000 and back to low at 3800.
 
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