Fuel pump control module

[Scooby2.5]

Which is what I was intending on doing until I saw scoooby's post above, advising to use the original power wire from factory fuel pump relay that would normally go to the fpc, as the trigger wire for my new relay

 

Yea as some of the other guys pictures show they ran and large gauge wire from the battery to a block in the back. Then fed the relay and the module if I remember correctly.

 

I did forget to mention that this last time but of course you have to feed the module something or it wouldn't be powered at all.

 

Sorry about that

 

Again you could try feeding the module off the new relay and running larger wire from the module to the pump and see what it does. Either way you are still feeding the module more voltage than before.

[dr20t]

Ok I'm going to really sound like a douche but i will still ask for the sake of clarity:

 

Scooby this question is directed at you: are you suggesting I use a normal four pin mechanical relay, or a solid state relay?

 

If normal mechanical one, and if I'm using it to power the fuel pump directly (bypassing high voltage to the fpc) will this be able to cope with the pwm regulation that the fpc controller will be providing?

 

If solid state, then doesn't the solid state relay need to be triggered via the negative wire of the fpc module output. I.e - negative from fpc to negative /ground on input side of the solid state relay? The reason I ask is because my learnings have been that using a solid state relay to control a variable voltage (pwm modulation for example) will need to be switched via negative trigger. Is this how I would do it?

 

I'm also now confused because in post 493 above, you were referring to wiring the fuel pump directly from the new relay, and in doing so bypassing the high voltage through the fpc. Ie high battery voltage goes to fuel pump only and fpc gets whatever it would normally get from factory. However in posts 501 and 502 I think you're talking about running the fpc on the new high voltage - ie battery voltage will go through the fpc to the fuel pump.

 

Which one is the better option? I would have thought the first (ie battery positive wire to relay to fuel pump), in which case the first set of questions above remain pertinent.

 

*EDIT* - scrap the last two paragraphs - I know what you're saying now: because you have already wired your fpcm through a new relay and upgraded wiring, it will be easier to just upgrade your pos and neg wiring from fpcm to fuel pump and see what that does. If it gives you required voltage then perfect and no more stuffing around - if it doesn't, only then will you look to bypass high voltage through fpcm and instead go straight pos 10ag from the relay to fuel pump, triggered by pos from the fpcm wiring.

 

Thank you again

 

Mick

Edited August 4, 2013 by dr20t
I now understand

[Scooby2.5]

Ok I'm going to really sound like a douche but i will still ask for the sake of clarity:

 

Scooby this question is directed at you: are you suggesting I use a normal four pin mechanical relay, or a solid state relay?

 

If normal mechanical one, and if I'm using it to power the fuel pump directly (bypassing high voltage to the fpc) will this be able to cope with the pwm regulation that the fpc controller will be providing?

 

If solid state, then doesn't the solid state relay need to be triggered via the negative wire of the fpc module output. I.e - negative from fpc to negative /ground on input side of the solid state relay? The reason I ask is because my learnings have been that using a solid state relay to control a variable voltage (pwm modulation for example) will need to be switched via negative trigger. Is this how I would do it?

 

I'm also now confused because in post 493 above, you were referring to wiring the fuel pump directly from the new relay, and in doing so bypassing the high voltage through the fpc. Ie high battery voltage goes to fuel pump only and fpc gets whatever it would normally get from factory. However in posts 501 and 502 I think you're talking about running the fpc on the new high voltage - ie battery voltage will go through the fpc to the fuel pump.

 

Which one is the better option? I would have thought the first (ie battery positive wire to relay to fuel pump), in which case the first set of questions above remain pertinent.

 

*EDIT* - scrap the last two paragraphs - I know what you're saying now: because you have already wired your fpcm through a new relay and upgraded wiring, it will be easier to just upgrade your pos and neg wiring from fpcm to fuel pump and see what that does. If it gives you required voltage then perfect and no more stuffing around - if it doesn't, only then will you look to bypass high voltage through fpcm and instead go straight pos 10ag from the relay to fuel pump, triggered by pos from the fpcm wiring.

 

Thank you again

 

Mick

 

Ok first off the POSITIVE lead to the pump is not PWM

 

Only the NEGATIVE lead is.

 

Just use a regular old good quality relay to turn on and off the direct battery feed from the battery using the old fuel pump relay signal

 

 

Now you have two choices. Off this new battery fed relay.......

 

1. Feed the FPCM

 

2. Feed the pump direct

 

 

The NEGATIVE lead off the FPCM is THE PWM signal.

 

Just run a larger wire from the FPCM connector to negative side of the pump.

 

 

Lets say your alt/batt voltage is 14v

 

The POSITIVE side of the pump will have 14v if you wire direct to the pump off new relay.

 

If you feed the module off the new relay and go through the module to feed the pump like factory you may have a smaller voltage on the positive side like say 13.7

 

 

This drop could cause the potential difference between the neg PWM signal and the positive to not quite be the 13.5 or above you need. It depends on how much voltage on the positive side the module drops on its output.

 

So do it however you want and see what you get.

 

 

The negative side (PWM signal) is not relayed or anything. You just run a larger wire from the module to the pump so there is less voltage drop on the changing ground.

 

This make sense?

 

Feel free to correct me if I'm wrong Frank

Edited August 4, 2013 by Scooby2.5

[dr20t]

Completely understand all of that as I did before. I know the positive output of the fpcm is not pwm. I also understand that its my choice whether to run direct to the pump or to the fpcm.

 

However, ( im sorry im honestly not nit picking here but trying to be clear) - again you've suggested to use the standard fpcm input power wire (from the factory fuel pump relay in the engine bay) to trigger the relay. If i was running the new high voltge output from the new relay to the fpcm then yes this would work.

 

But if im running the high voltage wire from new relay to the pump direct, then it wont work as the fpcm will still need a power input. In this case, do you mean to say that I should splice into this wire to trigger the relay (ie parallel circuit), such that the wire still continues to the fpcm but also supplies a feed through another wire to the relay? Won't this overload the circuit?

 

 

The way I see it is id like to run a large positive polarity wire from battery to new relay to the fuel pump. The relay would be triggered by the positive output wire from the fpcm (the one that used to go to the fuel pump positive side)

 

Then I would run the negative from fpcm to the negative side of the fuel pump.

 

That way the fpcm is still receiving its factory power input (no change to wiring here), and the only difference is the fuel pump positive wire is now coming through a new relay feeding battery voltage.

 

This is what I said in my original post, but you and heiche asked why I'm trying to do it differently and it wouldn't work.

 

Just trying to clarify if this would work and if so would I need a solid state relay or just a normal four pin mechanical relay

 

Sorry for the headaches

 

 

Mick

[Scooby2.5]

Completely understand all of that as I did before. I know the positive output of the fpcm is not pwm. I also understand that its my choice whether to run direct to the pump or to the fpcm.

 

However, ( im sorry im honestly not nit picking here but trying to be clear) - again you've suggested to use the standard fpcm input power wire (from the factory fuel pump relay in the engine bay) to trigger the relay. If i was running the new high voltge output from the new relay to the fpcm then yes this would work.

 

Correct, actually that relay is under the dash on passenger side in the US, only the fuse is in the bay in the fuse block (JUST for Clarity sake)

 

But if im running the high voltage wire from new relay to the pump direct, then it wont work as the fpcm will still need a power input. In this case, do you mean to say that I should splice into this wire to trigger the relay (ie parallel circuit), such that the wire still continues to the fpcm but also supplies a feed through another wire to the relay? Won't this overload the circuit?

 

Correct, like I said before, some have run the wire from the battery to a distribution block. From the block run one wire to the FPCM (in place of the factory fuel pump relay low voltage lead) and also run a wire from the block to the relay which in turn would go to the pump. The reason for this is powering the FPCM with batt voltage instead of the voltage that was dropping through the car from the factory fuel pump relay.

 

You could also in theory, splice the "low voltage wire from the stock relay" and feed it to the new relay as the "on' signal and also feed it back to the FPCM (like the factory), but the output is going to be less if you choose to come off the module for the positive lead.

 

The way I see it is id like to run a large positive polarity wire from battery to new relay to the fuel pump. The relay would be triggered by the positive output wire that used to go to the fpcm?

 

 

Then I would run the negative from fpcm to the negative side of the fuel pump.

 

That way the fpcm is still receiving its factory power input (no change to wiring here), and the only difference is the fuel pump positive wire is now coming through a new relay feeding battery voltage.

 

yes that will work fine and is the way zorro did it on NASIOC. I If it were me though, I would increase the guage of the wire coming from the FPCM connector NEG, to the pump. The pins pop out of that connector and you can solder a new larger guage wire for the negative side. You honestly dont want to skimp on wire size here either. The STI wiring is larger on both the positive wire out of the module and the PWM wire (NEG) out of the module

 

This is what I said in my original post, but you and heiche asked why I'm trying to do it differently and it wouldn't work.

 

Guess we were not understanding what you were saying, Sorrry

 

Just trying to clarify if this would work and if so would I need a solid state relay or just a normal four pin mechanical relay

 

Sorry for the headaches

 

 

Mick

 

 

What I plan to do to mine is put larger gauge wire from the module to the pump on both the negative and positive wires just like the STI.

 

Then I am going to feed the FPCM with the relayed battery voltage with the DW kit. This way I have max voltage going to the Module (just like the STI)

 

I will use the TINY old feed line that went to the module to turn "on" the relay.

 

That is the way mine is wired now, I just dont have the larger guage wire running from the module connector to the pump.

 

I purchased a factory STI fuel pump plug and I am going to splice it in or remove the pins and wires to make it as factory as possible.

 

 

The whole point to this was not only was the STI using larger guage wire to and from the module to the pump.

 

The STI had larger wire with more voltage feeding the Module off the fuel pump relay.

 

Our factory wire off the fuel pump relay (actually under the dash on passenger side in US) is too small and drops way too much voltage to use as a feed to the STI module. I guess you can but Im trying to mimick the STI setup and see what happens.

 

If it doesnt work, Ill run the positive side to the pump, feed the module with the factory voltage lead, and use the larger wire from the module to the pump on the negative side as you suggest.

 

Good luck!

Edited August 4, 2013 by Scooby2.5

[frank_ster]

some one can try running a solid state relay and see what the gain is . it should be the same as changing to a sti fpcm but require wiring.

 

edit:

 

but upgrading the wiring to larger requires wiring.

 

i dont think its nessasary for the fpcm to have more power . it acts like a solid state relay. it uses low currant signal to produce high currant output.

and it only works on the negative side of the pump. the positive wire just passes through.

Edited August 4, 2013 by frank_ster

[frank_ster]

for others to try you can get the alternator to pump out 14.5 volts if you remove the fuse. the park warning and alternator/ battery light may light up. but your system voltage should be raised.

. something to try.

[Scooby2.5]

The diode trick works great, and the MK3 fuse with diode I posted works GREAT and is factory like. Its a bit expensive but by the time you purchase the wire if you dont have any, and make one up like others have done to plug into the fuse block its worth it I think, but I am OCD a bit...LOL

[Scooby2.5]

dr20t if you are in AUS, I would def get the fuse from hkb like I posted earlier.

[dr20t]

Firstly thanks again frank and scooby:

 

A few things:

 

 

impressive sounding car! however i don't think you can use the square wave output of the fpcm to drive a relay, it is too high of a frequency.

 

you can run a heavy wire from batt (with an inline fuse near the batt connection) or from the switched green wire in the steering column back to the trunk to the new relay's pin 87. cut the existing fpcm supply wire (fpcm pin 10) and the harness side connects to relay pin 86. the fpcm side of the cut wire goes to relay pin 30. run relay pin 85 to chassis ground screw. all of that is just to get full power to the fpcm.

 

you can also replace the wires with heavier gauge going from fpcm to fuel pump, and from fpcm to ground.

 

 

Correct output wire of FPCM will not control relay as heiche said.

 

 

You have to do it like many others have said and the many drawings in this thread.

 

The wire from the stock Fuel pump relay is used to trigger the new relay.

 

dr20t Why change it from what the pump manufacturers recommend?

 

.

 

The above comments indicate you can't use the fpcm positive output to trigger the relay. Is this correct? (The relay I would be trying to trigger here will send battery voltage straight to the fuel pump not though the fpcm)

 

 

 

What I plan to do to mine is put larger gauge wire from the module to the pump on both the negative and positive wires just like the STI.

 

Then I am going to feed the FPCM with the relayed battery voltage with the DW kit. This way I have max voltage going to the Module (just like the STI)

 

I will use the TINY old feed line that went to the module to turn "on" the relay.

 

That is the way mine is wired now, I just dont have the larger guage wire running from the module connector to the pump.

 

I purchased a factory STI fuel pump plug and I am going to splice it in or remove the pins and wires to make it as factory as possible.

 

 

The whole point to this was not only was the STI using larger guage wire to and from the module to the pump.

 

The STI had larger wire with more voltage feeding the Module off the fuel pump relay.

 

Our factory wire off the fuel pump relay (actually under the dash on passenger side in US) is too small and drops way too much voltage to use as a feed to the STI module. I guess you can but Im trying to mimick the STI setup and see what happens.

 

If it doesnt work, Ill run the positive side to the pump, feed the module with the factory voltage lead, and use the larger wire from the module to the pump on the negative side as you suggest.

 

Good luck!

 

Again I know what you're saying and have very clearly understood this point from the beginning. However I think we're getting mixed up about what I'm referring to here.

 

I never intended at any stage to use the positive of the fpcm to go to the pump. This was always going to be through the new relay I ran so as to deliver the new higher voltage direct to the fuel pump (not through the fpcm).

 

Also, you're still suggesting to run higher voltage through the fpcm, although several pages ago, when you first linked the nasioc thread and zorro's work, i thought you were saying his way is a better way to do it? That way you don't risk voltage drop through the fpcm?

 

I'm happy to run it through the fpcm or not - it doesn't bother me either way. Just trying to figure out the best way to wire it and retain full pwm from the fpcm, whilst getting maximum possible voltage to the pump.

 

My logic here was if I'm running direct battery voltage to the fuel pump via a relay/ 10ag wire, there was no need to run the same high voltage to the fpcm, as really we would only be using the fpcm for the negative output to regulate fuel pump voltage and thus duty cycle. To achieve this, the fpcm will not need huge positive voltage, as long as I upgrade the negative output of fpcm to the pump to a minimum size of 12ag.

 

 

 

When you quoted me above, as follows:

 

Completely understand all of that as I did before. I know the positive output of the fpcm is not pwm. I also understand that its my choice whether to run direct to the pump or to the fpcm.

 

However, ( im sorry im honestly not nit picking here but trying to be clear) - again you've suggested to use the standard fpcm input power wire (from the factory fuel pump relay in the engine bay) to trigger the relay. If i was running the new high voltge output from the new relay to the fpcm then yes this would work.

 

Correct, actually that relay is under the dash on passenger side in the US, only the fuse is in the bay in the fuse block (JUST for Clarity sake)

 

But if im running the high voltage wire from new relay to the pump direct, then it wont work as the fpcm will still need a power input. In this case, do you mean to say that I should splice into this wire to trigger the relay (ie parallel circuit), such that the wire still continues to the fpcm but also supplies a feed through another wire to the relay? Won't this overload the circuit?

 

Correct, like I said before, some have run the wire from the battery to a distribution block. From the block run one wire to the FPCM (in place of the factory fuel pump relay low voltage lead) and also run a wire from the block to the relay which in turn would go to the pump. The reason for this is powering the FPCM with batt voltage instead of the voltage that was dropping through the car from the factory fuel pump relay.

 

You could also in theory, splice the "low voltage wire from the stock relay" and feed it to the new relay as the "on' signal and also feed it back to the FPCM (like the factory), but the output is going to be less if you choose to come off the module for the positive lead.

 

The way I see it is id like to run a large positive polarity wire from battery to new relay to the fuel pump. The relay would be triggered by the positive output wire that used to go to the fpcm?

 

 

 

Then I would run the negative from fpcm to the negative side of the fuel pump.

 

That way the fpcm is still receiving its factory power input (no change to wiring here), and the only difference is the fuel pump positive wire is now coming through a new relay feeding battery voltage.

 

yes that will work fine and is the way zorro did it on NASIOC. I If it were me though, I would increase the guage of the wire coming from the FPCM connector NEG, to the pump. The pins pop out of that connector and you can solder a new larger guage wire for the negative side. You honestly dont want to skimp on wire size here either. The STI wiring is larger on both the positive wire out of the module and the PWM wire (NEG) out of the module

 

This is what I said in my original post, but you and heiche asked why I'm trying to do it differently and it wouldn't work.

 

Guess we were not understanding what you were saying, Sorrry

 

Just trying to clarify if this would work and if so would I need a solid state relay or just a normal four pin mechanical relay

 

Sorry for the headaches

 

 

Mick [\QUOTE]

 

 

Whichever way I do it, I'm going to run a minimum 12ag negative wire from fpcm to negative side of fuel pump.

 

In terms of the new relay trigger, if I use the factory power wire to the fpcm, my plan was to unsheath some of the wire, twist and solder a new short length of wire from this to the relay, and that way use the factory wire to both trigger the new relay and send power to the fpcm.

 

 

dr20t if you are in AUS, I would def get the fuse from hkb like I posted earlier.

 

Already ordered one -

 

Thank you for the tip on this one.

 

Keen to have this all wrapped up today if possible.

 

Mick

[KCwagon]

QUOTE : "In terms of the new relay trigger, if I use the factory power wire to the fpcm, my plan was to unsheath some of the wire, twist and solder a new short length of wire from this to the relay, and that way use the factory wire to both trigger the new relay and send power to the fpcm."

 

This is the way I have mine wired. The factory FPCM power wire powers both the FPCM and the relay. Direct power to FP from the battery. 12g wire for both the + and - to and from the FP and FPCM. I am seeing 13.5 volts at 100% FP duty cycle. I am only running a DW65c and I am fairly sure that I could run a larger FP and not need to worry about the amperage draw.

[dr20t]

That's awesome thanks kc

 

Is the current draw to turn the relay on significant enough to cause any issues with the fpcm / original fuel pump circuitry.

 

Also - any reason to suspect the old schools type mechanical relay will not be up to the task of constant pulse width modulation of the fpcm?

 

Frank's suggestion above was to use a solid state relay - this would require a rethink of the wiring would it not?

 

As per one of my previous posts, my understanding is when using solid state relays in a system with pwm, the negative output of the pwm controller (in our case the fpcm) needs to go to the input side of the solid state relay itself - is this correct?

Edited August 5, 2013 by dr20t

[frank_ster]

mechanical relay on positive

relays draw very little power to activate.

 

the solid state relay would go on the negative.

 

prehaps we should draw you a diagram so you can better understand ..

 

fyi the fpcm is basically a solid state relay.

 

the fuel pump operates like injectors as the 12v positive is on with the key and the negative is pulsed to create variable speed.

 

what you can do to get started is run the larger wire from battery to the back area.

 

and change out to bigger wires.

[Scooby2.5]

Firstly thanks again frank and scooby:

 

A few things:

 

 

 

 

 

 

 

The above comments indicate you can't use the fpcm positive output to trigger the relay. Is this correct? (The relay I would be trying to trigger here will send battery voltage straight to the fuel pump not though the fpcm)

 

 

 

 

 

Again I know what you're saying and have very clearly understood this point from the beginning. However I think we're getting mixed up about what I'm referring to here.

 

I never intended at any stage to use the positive of the fpcm to go to the pump. This was always going to be through the new relay I ran so as to deliver the new higher voltage direct to the fuel pump (not through the fpcm).

 

Also, you're still suggesting to run higher voltage through the fpcm, although several pages ago, when you first linked the nasioc thread and zorro's work, i thought you were saying his way is a better way to do it? That way you don't risk voltage drop through the fpcm?

 

I'm happy to run it through the fpcm or not - it doesn't bother me either way. Just trying to figure out the best way to wire it and retain full pwm from the fpcm, whilst getting maximum possible voltage to the pump.

 

My logic here was if I'm running direct battery voltage to the fuel pump via a relay/ 10ag wire, there was no need to run the same high voltage to the fpcm, as really we would only be using the fpcm for the negative output to regulate fuel pump voltage and thus duty cycle. To achieve this, the fpcm will not need huge positive voltage, as long as I upgrade the negative output of fpcm to the pump to a minimum size of 12ag.

 

 

 

When you quoted me above, as follows:

 

Completely understand all of that as I did before. I know the positive output of the fpcm is not pwm. I also understand that its my choice whether to run direct to the pump or to the fpcm.

 

However, ( im sorry im honestly not nit picking here but trying to be clear) - again you've suggested to use the standard fpcm input power wire (from the factory fuel pump relay in the engine bay) to trigger the relay. If i was running the new high voltge output from the new relay to the fpcm then yes this would work.

 

Correct, actually that relay is under the dash on passenger side in the US, only the fuse is in the bay in the fuse block (JUST for Clarity sake)

 

But if im running the high voltage wire from new relay to the pump direct, then it wont work as the fpcm will still need a power input. In this case, do you mean to say that I should splice into this wire to trigger the relay (ie parallel circuit), such that the wire still continues to the fpcm but also supplies a feed through another wire to the relay? Won't this overload the circuit?

 

Correct, like I said before, some have run the wire from the battery to a distribution block. From the block run one wire to the FPCM (in place of the factory fuel pump relay low voltage lead) and also run a wire from the block to the relay which in turn would go to the pump. The reason for this is powering the FPCM with batt voltage instead of the voltage that was dropping through the car from the factory fuel pump relay.

 

You could also in theory, splice the "low voltage wire from the stock relay" and feed it to the new relay as the "on' signal and also feed it back to the FPCM (like the factory), but the output is going to be less if you choose to come off the module for the positive lead.

 

The way I see it is id like to run a large positive polarity wire from battery to new relay to the fuel pump. The relay would be triggered by the positive output wire that used to go to the fpcm?

 

 

 

Then I would run the negative from fpcm to the negative side of the fuel pump.

 

That way the fpcm is still receiving its factory power input (no change to wiring here), and the only difference is the fuel pump positive wire is now coming through a new relay feeding battery voltage.

 

yes that will work fine and is the way zorro did it on NASIOC. I If it were me though, I would increase the guage of the wire coming from the FPCM connector NEG, to the pump. The pins pop out of that connector and you can solder a new larger guage wire for the negative side. You honestly dont want to skimp on wire size here either. The STI wiring is larger on both the positive wire out of the module and the PWM wire (NEG) out of the module

 

This is what I said in my original post, but you and heiche asked why I'm trying to do it differently and it wouldn't work.

 

Guess we were not understanding what you were saying, Sorrry

 

Just trying to clarify if this would work and if so would I need a solid state relay or just a normal four pin mechanical relay

 

Sorry for the headaches

 

 

Mick [\QUOTE]

 

 

Whichever way I do it, I'm going to run a minimum 12ag negative wire from fpcm to negative side of fuel pump.

 

In terms of the new relay trigger, if I use the factory power wire to the fpcm, my plan was to unsheath some of the wire, twist and solder a new short length of wire from this to the relay, and that way use the factory wire to both trigger the new relay and send power to the fpcm.

 

 

 

 

Already ordered one -

 

Thank you for the tip on this one.

 

Keen to have this all wrapped up today if possible.

 

Mick

 

oy vey! Id say send me a PM, Ill give you my number and you can call me at this point

 

Seems you are making this waaaaaay harder than it is IMHO.

 

Now you are talking about controlling the new relay with the positive output of the FPCM.

 

I guess you could but why would you want to?

[Scooby2.5]

QUOTE : "In terms of the new relay trigger, if I use the factory power wire to the fpcm, my plan was to unsheath some of the wire, twist and solder a new short length of wire from this to the relay, and that way use the factory wire to both trigger the new relay and send power to the fpcm."

 

 

"Correct, like I said before, some have run the wire from the battery to a distribution block. From the block run one wire to the FPCM (in place of the factory fuel pump relay low voltage lead) and also run a wire from the block to the relay which in turn would go to the pump. The reason for this is powering the FPCM with batt voltage instead of the voltage that was dropping through the car from the factory fuel pump relay."

 

 

Shawn and I are both saying the same thing here.

 

Simply splicing the feed wire and sending it to two places:

1. to the relay coil

2. to the FPCM input

 

Whether it is the factory wire from the fuel pump relay, or battery voltage from the wire we ran from the battery.

Edited August 5, 2013 by Scooby2.5

[dr20t]

Haha I do get it frank, really . I know the fpc is basically a solid state - thus the negative regulationod voltage.

 

I understand now about the solid state being for the negative side. I previously didnt realize this

 

It's honestly not complicated at all - all I basically wanted to know is whether its ok to switch the positive side relay (which will power the fuel pump direct) with the same power wire that feeds the fpcm. Which you have now answered as yes

 

And also whether to use a normal relay or solid state - and I now take it that I should run a mechanical relay to the positive side of the fuel pump.

 

So that means the negative side from fpcm wil already be running though solid state relay (being the fpcm itself) so nothing else needs to change

 

To summarize / finalize:

 

1. 10ag wire from battery, fused close to the battery, and run to a mechanical 4 pin 30/40 amp relay.

 

2. Trigger for relay to come from factory fpcm power wire, and continue to feed the fpcm as well

 

3. Positive output from relay via 10ag wire to fuel pump positive terminal

 

4. Upgrade fpcm negative output wire to 10/12ag (whatever I can fit into the terminal) and run this to negative side of fuel pump

 

5. Tape up / discontinue using positive output wire from fpcm - just insulate it.

 

6. If I really want to be keen, I can also upgrade positive wire to fpcm so as to reduce voltage drop, which can be done in a couple of ways

 

I'm sure this will achieve the outcome - which is to get 13.6-13.8v at the fuel pump, yet still have pwm regulation via the fpcm

 

Mick

[Scooby2.5]

mechanical relay on positive

relays draw very little power to activate.

 

the solid state relay would go on the negative.

 

prehaps we should draw you a diagram so you can better understand ..

 

fyi the fpcm is basically a solid state relay.

 

the fuel pump operates like injectors as the 12v positive is on with the key and the negative is pulsed to create variable speed.

 

what you can do to get started is run the larger wire from battery to the back area.

 

and change out to bigger wires.

 

What would be the purpose of relaying the negative signal that is essentially the ground reference whether it is 0,6 or 8 volts?

 

so in essence why relay the PWM signal going out of the module to the pump?

[Scooby2.5]

"Also, you're still suggesting to run higher voltage through the fpcm, although several pages ago, when you first linked the nasioc thread and zorro's work, i thought you were saying his way is a better way to do it? That way you don't risk voltage drop through the fpcm?

 

I'm happy to run it through the fpcm or not - it doesn't bother me either way. Just trying to figure out the best way to wire it and retain full pwm from the fpcm, whilst getting maximum possible voltage to the pump."

 

 

I was merely trying to say you can run higher voltage to the module and it should be enough to the pump through the module.

 

OR

 

You can run the voltage from the battery straight to the pump via the relay.

 

Either way will work I think.

 

YOU WILL get more voltage to the pump by going direct through the relay instead of through the relay and through the module.

 

The reason I said zorro's is better is because then you dont need to worry about a voltage drop through the module on the positive side.

 

Once I realized from Frank and my own testing that the PWM signal is the ground side, I realized you may as well run voltage straight to the pump via the new relay and let the module just worry about the negative lead.

 

Seems a bit more safe to me this way.....

Edited August 5, 2013 by Scooby2.5

[dr20t]

Crystal clear now

 

The only reason I suggested looking into solid state relay was this is what frank suggested. I think between you and frank I was confused as at times there was conflicting advice which at times was contradictory to your own original posts.

 

All good and will proceed with the setup I detailed above in post 517

 

My apologies for any frustration caused and will report back with findings / details

 

Mick

[frank_ster]

What would be the purpose of relaying the negative signal that is essentially the ground reference whether it is 0,6 or 8 volts?

 

so in essence why relay the PWM signal going out of the module to the pump?

 

well to remove the fpcm from any load what so ever.

 

as i said it can be like replacing the fpcm from a sti..

 

just go to the pump directly cut the wires off the two wires going to the pump simply become mechanical relay on the + and solid state on the -. new battery power to the relay and new ground to the soild state and thats it.

 

i say this because i assume there is voltage drop on the positive and voltage raise on the negative leaving the fpcm.

 

i should just draw a diagram..

[dr20t]

But if the fpcm is in actuality a quasi solid state relay then there's no need for that is there?

 

We have adduced that the duty cycle is achieved via fpcm negative output to the pump varying the earthing voltage. Therefore I'd rather leave it to do its job and just change the size of the wire so as to match the positive output going to the pump.

 

Surely this would be the best way without overly complicating it with another solid state relay to achieve the same thing (especially when I just paid $100 for the wrx Sti fpcm )

[frank_ster]

well it just depends on the voltage you get across the pump. don't measure from ground to the positive of the pump. you need to measure from positive to negative.

 

its a solid state relay designed for half of the currant your putting through it.

[dr20t]

Fair point about it being designed for less current (albeit the exact current it was designed for is unknown as far as I'm aware ?)

 

I think for now ill chance it, given others haven't had any dramas for over a year. If the fpcm fails due to the high current draw passing through it then I will look into the solid state relay.

 

For information sake - I'm assuming you'd still keep the fpcm in place although negative output from fpcm would go to the solid state relay input trigger, and output from the solid state relay would go to the negative side of the pump? Trigger would come from the same wire as the mechanical relay (ie the factory power wire to the fpcm)?

[frank_ster]

Fair point about it being designed for less current (albeit the exact current it was designed for is unknown as far as I'm aware ?)

 

I think for now ill chance it, given others haven't had any dramas for over a year. If the fpcm fails due to the high current draw passing through it then I will look into the solid state relay.

 

For information sake - I'm assuming you'd still keep the fpcm in place although negative output from fpcm would go to the solid state relay input trigger, and output from the solid state relay would go to the negative side of the pump?

yes

 

Trigger would come from the same wire as the mechanical relay (ie the factory power wire to the fpcm)?

 

waa?

[dr20t]

So I completed the wiring upgrade today

 

Ended up having to retain the stock fuel pump plug. Left about an inch of negative and positive wiring to the plug, then 10ag wiring to the relay for positive, and 10ag wiring to the fpcm for the negative.

 

Haven't measured the voltage yet as I ran out of daylight - will check tomorrow and report the results.

 

Thanks to all who contributed to this thread for the help.

 

Mick