PWM and fuel pump wiring
I've read through the different threads and can't find a for sure answer to this: Does the ECM control the fuel pump output using pulse width modulation? Is there a reason I can't take that tiny 16 ga orange wire and run a 10 ga back to the pump directly from the junction bar so I know the pump isn't hurting for power? If I run a relay to protect the circuit, I would have to use the orange wire as the "high voltage" side, correct? My fuel pump wiring circuit is just over 18 feet one way, and at the amperage my pump is rated, 10 gauge is the smallest I should go. The only way I can see that the handheld can tell you what percentage the pump is running at is if it's being controlled before it even starts pumping.
Yes, I'm running a dedicated 10 ga ground to the pump also.
Yes. The ECM controls the pump using PWM. I don't see any problem cutting their orange wire and replacing it with a larger wire. I did the same for the off-engine side of the harness, but you could do it right where it comes off the unit. However, keep in mind that by doing it you will be voiding Fitech's warranty. I think these have a 1-year warranty so if you are past that time then it may not matter. Mine is connected to the harness without relay and as you know I added a properly rated connector for the pump and 12v feed. I also have a 15amp fuse next to the pump for added protections since 15 amps is the maximum recommended by Fitech.
In regards to a relay, the reason to add it is to lower the power going through that orange wire. That said, the orange wire will connect to the "low" power side of the relay (85 and 86 which drive the coil). If connected to the "high" side, if I understand what you mean with it, then the relay won't do anything and you will still get high power through the orange wire. Keep in mind that by adding the relay you lose the PWM control and you will want to set it up to 100%. The fuel flow will be controlled by the pressure regulator and the tank return line. I read somewhere that you may be able to use a special type of relay (digital?) that may be able to keep the PWM functionality. However, I don't really know much about it.
That's what I was thinking was going to happen with the relay. Not worried about the warranty, unit is several years old already and I've spliced in a few things already. I think I will just upgrade the orange wire to a larger gauge, as well as the red power in wire and let the unit continue to control the pump output with PWM. I think the advantages of that overwhelm the advantages of having a relay. I've cut out the additional wiring related to the kill switch, so the entire run is 18 feet from the connector to the pump, including the inertia switch detour. I used 1o ga. high quality US made fine strand copper wire, and threw a 15 amp mini-ANL fuse in were the wiring gauge changes. We will see what happens... The FiTech must be able to put out enough amperage to run the pumps or other folks would be having issues all the time. I think you are like me in that you like to have a little more cushion instead of running everything right at the maximum all the time....thanks for the help and advice on this!
By the way, do you know of a place where the electrical specs for the FiTech units are listed? I got a few with the instructions, but I'm looking for a more comprehensive list...for one the operating voltage range for the units.
Good idea about the inertia switch. I added a relay to the ignition wire to the EFI as an ignition kill. I can use that same circuit with an inertia switch to kill the power to the EFI.
Which inertia switch did you use?
So I have been following this post. I have an intank warbo 255, feed my go EFI 400, with a return line. What caught my eye was the PWM. Warbo tells you to turn PWM off Or you will burn up the pump. I think I even seen if on the FiTech site. Maybe I don’t fully understand, but I am reading guys still using PWM with NON FiTech pumps. Is this a problem or internet lore?
Oh yea. No relay either.
Quote from vjp38 on April 29, 2020, 4:42 pmSo I have been following this post. I have an intank warbo 255, feed my go EFI 400, with a return line. What caught my eye was the PWM. Warbo tells you to turn PWM off Or you will burn up the pump. I think I even seen if on the FiTech site. Maybe I don’t fully understand, but I am reading guys still using PWM with NON FiTech pumps. Is this a problem or internet lore?
My external pump doesn't take PWM either, so I had to wire that separately with relay from ignition so that runs all the time with the engine on. As long as your return pressure relief valve is working on your fitech, you shouldn't have an issue returning the excess fuel back to the tank. My return relief valve failed eventually, as evidenced by the fuel pressure at the inlet of the fitech going up to 100 psi, the pressure of the pump, so I had to also put in my own external pressure relief valve and return to the tank, and plug off the return line from the fitech. The advantage to this was that I could set my inlet pressure to the fitech to anything I wanted and opted for 58 psi, even though the fitech pressure relief valve was a 43 psi on the meanstreet 800 system, essentially bumping up my fuel delivery capability to 1000 hp instead of 800.
The easy question first: pulled the inertia switch off a Crown Victoria at the junkyard...it was located in the trunk, driver's side, under the liner. I think most Fords have them into the late 2000's, then they became integrated with the pcm and other computer crap, so you can't use the switch alone. If it's just got two wires going to it, it's a winner, usually has a red button somewhere on the top.
As far as the PWM and fuel pressure question, I don't know enough about electronics to answer that...but I think if the pump manufacturer says don't use it, I'd probably not use it. PWM doesn't cooperate well with a lot of electrical motors, I do know that. Unless it was set up from the beginning to be a variable speed motor, I think it shortens the life of the motor. It slows the speed by starving the motor for electricity in a set pattern, so it's kind of like turning it on and off repeatedly to keep it from reaching full speed. I'm sure there's an electrical genius on here who can explain it better than that, hopefully. When I go into the boonies, I always carry a spare fuel pump, just because it seems to me that is one of the weaker links on the system. Mine hasn't failed yet, so I can say it won't burn it out right away, but that's about all I can tell you for sure. Replacing the pressure relief valve may be cheaper and easier than replacing your fuel pump.
Quote from bdhulderman on April 30, 2020, 8:08 amQuote from vjp38 on April 29, 2020, 4:42 pmSo I have been following this post. I have an intank warbo 255, feed my go EFI 400, with a return line. What caught my eye was the PWM. Warbo tells you to turn PWM off Or you will burn up the pump. I think I even seen if on the FiTech site. Maybe I don’t fully understand, but I am reading guys still using PWM with NON FiTech pumps. Is this a problem or internet lore?
My external pump doesn't take PWM either, so I had to wire that separately with relay from ignition so that runs all the time with the engine on. As long as your return pressure relief valve is working on your fitech, you shouldn't have an issue returning the excess fuel back to the tank. My return relief valve failed eventually, as evidenced by the fuel pressure at the inlet of the fitech going up to 100 psi, the pressure of the pump, so I had to also put in my own external pressure relief valve and return to the tank, and plug off the return line from the fitech. The advantage to this was that I could set my inlet pressure to the fitech to anything I wanted and opted for 58 psi, even though the fitech pressure relief valve was a 43 psi on the meanstreet 800 system, essentially bumping up my fuel delivery capability to 1000 hp instead of 800.
How did you know the pressure was too high at the inlet? Would adding an aftermarket fuel pressure regulator in line just before the inlet to the Fitech have avoided this issue? I'm thinking of putting a GM style adjustable regulator on the fuel line, that way the pressure would be reduced to just about what the fitech wanted prior to it getting there. I could use the same return line, I'd just have to add a couple of AN t's and the regulator and pressure gauge. Added benefit of having the ability to switch to using either system alone in a pinch if one fails. I'm trying to head off any failures while I'm hundreds of miles from the nearest gas station, now that you brought this up, I'm going to have to have a plan in case it happens to me!
Quote from tony-muscle on April 28, 2020, 10:28 amYes. The ECM controls the pump using PWM. I don't see any problem cutting their orange wire and replacing it with a larger wire. I did the same for the off-engine side of the harness, but you could do it right where it comes off the unit. However, keep in mind that by doing it you will be voiding Fitech's warranty. I think these have a 1-year warranty so if you are past that time then it may not matter. Mine is connected to the harness without relay and as you know I added a properly rated connector for the pump and 12v feed. I also have a 15amp fuse next to the pump for added protections since 15 amps is the maximum recommended by Fitech.
In regards to a relay, the reason to add it is to lower the power going through that orange wire. That said, the orange wire will connect to the "low" power side of the relay (85 and 86 which drive the coil). If connected to the "high" side, if I understand what you mean with it, then the relay won't do anything and you will still get high power through the orange wire. Keep in mind that by adding the relay you lose the PWM control and you will want to set it up to 100%. The fuel flow will be controlled by the pressure regulator and the tank return line. I read somewhere that you may be able to use a special type of relay (digital?) that may be able to keep the PWM functionality. However, I don't really know much about it.
I've been thinking about this for a few weeks. It seems to me that if you were to use the orange wire on the high voltage side of the relay, and then use either an ignition hot or better yet the power up wire for the fitech unit as the coil driver, you would be able to keep the PWM and use the relay. The signal from the Fitech would be passing through the relay unmolested once the contacts close.
That being said, I can't really think of an advantage of doing this, and by adding another hurdle for the electricity to pass through, you probably reduce the voltage ultimately getting to the pump by a small amount. Since we are trying to increase the amount of power getting to the pump, I can't see this as being helpful.
By using the orange wire on the coil side of the relay, you may risk not triggering the relay if the PWM reduces the pump power to the point it won't trigger the relay or worse yet, starts to cycle the switch on and off with each pulse.
Hopefully some engineer at Fitech is paying attention to this and is already working on an improved system. Wouldn't be hard to do, but I think improving on what we have is more trouble than it's worth. Just upgrade the connectors and wire gauge and keep the run as short as possible.