FPCM, Dual Fuel Pumps and the green and white wire.

[FasNuf]

I wish I would have seen a thread like this when I first put my dual pump fuel system in my car, it would have save me a lot of confusion. I'm sure this is old hat to some, but I'm posting just so people that are having troubles might find it and get a help out.

Squash uses the pink #21 wire going to the FPCM to trip the relays to power their fuel pumps. #21 is referenced as ignition voltage.

Some want to use the D-GN/WH #20 green and white wire. #20 is referenced as the Fuel Pump Relay Control.

When I was testing which to use, my GRN/WHT didn't have voltage and when it did, it wasn't reading 12 volts. It just didn't seem reliable. I was a bit confused and had been trying to figure out some stuff with the can bus and codes at the same time. The pink wire had 12 volts at key ON and also while cranking. Thinking my relays primary windings were too much for the Green and white wire, I opted for the pink. If I had just disconnected the battery and wired the Grn/Wht up right away, there might not have been this problem.

I'm now using the green and white wire to trigger the relays and it's an improved way over the pink wire for triggering. More on that in a minute, but let me explain why it didn't work at first and what most don't know about this circuit.

On the stock system, you may not notice because it's pretty quiet, but when you first turn the key on in the morning, the fuel pump runs for a couple seconds and then shuts off. When you turn the ignition to start the car, the pump turns on and delivers fuel and the car starts. The fuel pump is Pulse Width Modulated and only spins the pump fast enough to maintain pressure in the rail as determined by the fuel pressure sensor.

Now one might think that the car realized that pressure was up high enough so the fuel pump turned off because its not needed, well, that's not really what takes place and was the source of my confusion. I assumed this is what was happening...it's not.

When the key is first turned to the on position, the green and white wire gets voltage for a specific amount of time, in the stock case, it's 2 seconds. After this 2 seconds, it doesn't have voltage until the key is turned to crank the engine, then it gets voltage to run the pumps. This initial 2 seconds is called the prime time. Turning the key off and even taking it out and then reinserting the key wont necessarily trip the 2 second priming timer again. Given enough time, it will trigger the priming timer again if turned ON.
The amount of time is adjustable in the HP Tuners Editor under FUEL SYSTEM>FUEL PUMP>PRIME TIME. Its adjustable from 2-410 seconds. No idea why you would want to prime that long, but it's there.

I've read and maybe someone knows more than I about this, but the GRN/WHT fuel pump circuit is able to shut the fuel pump off in case of an accident. This seems logical and an advantage over using the pink wire for triggering. Another advantage is the priming. I adjusted mine to 5 seconds to help get hot fuel off the engine after sitting for a few minutes. I don't have problems with vapor lock, but this might help in other areas of my tune.

Please contribute to my chaos, but don't roast me. I'm still learning HP Tuners and have a long way to go to be any good. I hope someone gets some help before getting confused like I did.

Cheers,
Mark

[JMI]

Yep, that's the wire that I used for the trigger wire for my Fore setup for a few years now.
You can also change the prime time (factory 2 seconds) in HP tuners. Think I have mine set between 5-8 seconds.

[FasNuf]

Originally Posted by JMI

Yep, that's the wire that I used for the trigger wire for my Fore setup for a few years now.
You can also change the prime time (factory 2 seconds) in HP tuners. Think I have mine set between 5-8 seconds.

yep, thats the screen shot that I included along with the pin out for the FPCM. It sure wouldve made my job easier if I knew how that wire worked and that it goes dead after a couple seconds...I thought something was wrong. Ha, wrench and learn.

[kpwalls06]

Glad to read this information, as I'm getting back into working on my Fore Innovations system now to try and clear a P018C code. I hadn't thought of using the green and white wire, but maybe that will help.

Also, if either of you on this thread have any input on clearing the P018C, I would greatly appreciate it! My first thought is to install a jumper to tell the system that the fuel sensor has pressure, but I'm wondering if switching to the GN/WH trigger wire would help?

Also need to check the prime time in my tune, as I have noticed that the car can take two cranks to start if it's just been stopped for a few minutes, such as stopping for gas.

[Risingson05]

Originally Posted by kpwalls06

Glad to read this information, as I'm getting back into working on my Fore Innovations system now to try and clear a P018C code. I hadn't thought of using the green and white wire, but maybe that will help.

Also, if either of you on this thread have any input on clearing the P018C, I would greatly appreciate it! My first thought is to install a jumper to tell the system that the fuel sensor has pressure, but I'm wondering if switching to the GN/WH trigger wire would help?

Also need to check the prime time in my tune, as I have noticed that the car can take two cranks to start if it's just been stopped for a few minutes, such as stopping for gas.

Idk if this will help but fore offers a fuel pressure sensor port and a pigtail to connect to ecm .

[FasNuf]

Originally Posted by kpwalls06

Glad to read this information, as I'm getting back into working on my Fore Innovations system now to try and clear a P018C code. I hadn't thought of using the green and white wire, but maybe that will help.

Also, if either of you on this thread have any input on clearing the P018C, I would greatly appreciate it! My first thought is to install a jumper to tell the system that the fuel sensor has pressure, but I'm wondering if switching to the GN/WH trigger wire would help?

Also need to check the prime time in my tune, as I have noticed that the car can take two cranks to start if it's just been stopped for a few minutes, such as stopping for gas.

First, the P018c can indicate a short so check your wiring. I have mine set to NO ERROR REPORTED and SES is unchecked. This is in the FPCM and will need to be licensed to flash.

Second, The prime time only affects a pump that is triggered by the Grn/Wht wire. If you're triggering the fuel relays with the pink wire, then they're always on if the key is on.

Finally, Assuming you're on a return system and not the stock returnless rails. If you're having hard to start issues after sitting, make sure you have a check valve in your supply line otherwise the fuel will return to the tank after shutting it down.

[kpwalls06]

Thanks for the input on the short, I'll double check that. And thanks for the clarification on the prime time and relation to the Green/White wire.

It is a return style system, and there is a check valve in the system, that was one of the things I double-checked the first time it happened. The more I've driven it I've narrowed it down, and now the only time I have trouble with the car starting is when it's already hot, and I've only had it off for a few minutes. Any time it's off for more than 10-15 minutes, even sitting for a few days, it starts on the first crank with no issues.

[FasNuf]

Can you see pressure on your fuel gauge after you shut the car off?

[kpwalls06]

Well it's a funny story, but the aftermarket pressure gauge quit working a little while back, so that's another issue I'm going to be working on.

[eLeSthree]

I thought I had made a thread about this. How the green/white wire acts, prime time, safety kill switch, the whole 9. It might be mixed in with another of my fuel system posts. It was difficult information to come by, for sure.

Thanks for putting it together in a single thread with a proper title, that will hopefully come up in future searches.

I used 4 seconds of prime time, since I had increased the volume of fuel lines so much. Worked better for me. -10 feed.

[eLeSthree]

Originally Posted by kpwalls06

Glad to read this information, as I'm getting back into working on my Fore Innovations system now to try and clear a P018C code. I hadn't thought of using the green and white wire, but maybe that will help.

Also, if either of you on this thread have any input on clearing the P018C, I would greatly appreciate it! My first thought is to install a jumper to tell the system that the fuel sensor has pressure, but I'm wondering if switching to the GN/WH trigger wire would help?

Also need to check the prime time in my tune, as I have noticed that the car can take two cranks to start if it's just been stopped for a few minutes, such as stopping for gas.

Have you deleted the Fuel pressure sensor? I relocated mine to the engine bay, just extended the harness with some wire. The ECM should know the FP. (FYI, dont put it on the fuel rail. noisy)

[FasNuf]

Originally Posted by eLeSthree

I thought I had made a thread about this. How the green/white wire acts, prime time, safety kill switch, the whole 9. It might be mixed in with another of my fuel system posts. It was difficult information to come by, for sure.

Thanks for putting it together in a single thread with a proper title, that will hopefully come up in future searches.

I used 4 seconds of prime time, since I had increased the volume of fuel lines so much. Worked better for me. -10 feed.

Hell, it was probably your thread i read that gave me the jump to do mine. Thank You

[FasNuf]

I have the sensor in the engine bay and I still see fluctuations on pressure. Do you guys see these too? I don’t want a dampener if I don’t need it

[eLeSthree]

No, it only rises with boost, but its mechanically controlled. If your pumps are powered off seperate relays, and you have a mech FPR the fpcm is only supplying the relay voltage and FP readings.

Where is the regulator plumbed into the system? Prefferably after the rails with return coming off the bottom.

Just checking but the green/white wire is only being used to relay one pump, and the other is relayed from a hobbs. Correct?