When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I know people use'em. But show me a REAL built race car or OEM car that would use a pressure switch to control a fuel pump. Too many failure modes there for me. If the LOAD is calculated by MAP only then I see what your saying about the fidelity of control being the same. I was under the impression (at least for the Evo X) that the load was much more involved than just MAP. If that was the case why have a LOAD value in the ECU at all and just reference everything from the MAP tables. I suspect there is more to the LOAD value. I did do some data diving and in my thread measured and plotted LOAD vs. BOOST and yes they are MOST of the time similar and linear but there is variance. The long term reliability is in question, Mitsubishi couldn't even get the switching correct for the Evo X and the fuel pump relays die like crazy. With big big pumps a progressive controller tied to injector duty cycle would be ideal.
I was thinking about something just like that, a boost-a-pump type power supply that took in an IPW signal, also maybe used a fuel pressure sensor to build up a learned look up table based on a user defined fuel pressure target. It just seems to make a lot of sense, the longer the fuel injectors are open the more fuel the pump has to flow. Same with pressure, the higher the fuel pressure the more power it needs.
I know people use'em. But show me a REAL built race car or OEM car that would use a pressure switch to control a fuel pump. Too many failure modes there for me. If the LOAD is calculated by MAP only then I see what your saying about the fidelity of control being the same. I was under the impression (at least for the Evo X) that the load was much more involved than just MAP. If that was the case why have a LOAD value in the ECU at all and just reference everything from the MAP tables. I suspect there is more to the LOAD value. I did do some data diving and in my thread measured and plotted LOAD vs. BOOST and yes they are MOST of the time similar and linear but there is variance. The long term reliability is in question, Mitsubishi couldn't even get the switching correct for the Evo X and the fuel pump relays die like crazy. With big big pumps a progressive controller tied to injector duty cycle would be ideal.
On the EvoX you get weird averaging because it mixes MAP and MAF.
This isn't an EvoX, it's an 8/9, and at that power it should be on speed density, which means load and map are interchangeable. Most EMS systems do use boost isn't of a load number on the timing and fuel tables actually...
You talk about failure modes with a Hobbs switch, but your method requires the addition of 2 or 3 relays. Sounds like just as much failure potential to me...
255 primary, 450 secondary. No problem with 600+ mustang on e85 with 1750s.
stock lines and both pumps have a 10ga 25amp dedicated power line
Thank you sir. Someone was running 255+450. I just thought, I would run 255 with stock wires and stock fuel line and 450 with hobbs switch using evap line as a fuel line for it.
Wait... do you do not have a rewire on the current 450 pump? That alone will likely fix your fuel needs if that's case...
I have hobbs switch+70amp relay+6mm2 wire for my 450. Kics around 10psi. People has been using this method with 450 for a while, so I did it too. The simplest way to improve this is just to swap to 525, but it is so hungry for the amps when running without boost (18A/13.5V at base 43psi fuel pressure). I don't dare to run it on stock wires (20A fuse). And I am not going to update the stock fuel pump wiring.
Looks like the stock wires can handle 450 on cruising (stock low/high voltage) and I could do double 450. But I would like to have 6mm2 wires for both pumps, when on boost. So the stock wires wouldn't overheat and both pumpd get good voltage. I know people run 450 twins and the 1st pump is only on stock wires, but I don't feel comfortable to do it.
On the EvoX you get weird averaging because it mixes MAP and MAF.
This isn't an EvoX, it's an 8/9, and at that power it should be on speed density, which means load and map are interchangeable. Most EMS systems do use boost isn't of a load number on the timing and fuel tables actually...
You talk about failure modes with a Hobbs switch, but your method requires the addition of 2 or 3 relays. Sounds like just as much failure potential to me...
The solid state relays I used have a 1000 year operating time. Sounds insane but it's in the data sheet for it. No moving parts, internal optical isolated. The thing is that if the ECU decides to kill power to the pump (aka: a crash!) You REALLY WANT All pumps turnoff. You would never want a scenario where a fuel pump is feeding a fire! I know people do the Hobbs method and I almost did too,. but instead went a safer and more reliable method. I documented everything here on this forum only. Just trying to help.
The solid state relays I used have a 1000 year operating time. Sounds insane but it's in the data sheet for it. No moving parts, internal optical isolated. The thing is that if the ECU decides to kill power to the pump (aka: a crash!) You REALLY WANT All pumps turnoff. You would never want a scenario where a fuel pump is feeding a fire! I know people do the Hobbs method and I almost did too,. but instead went a safer and more reliable method. I documented everything here on this forum only. Just trying to help.
1000 years? LOL do they put their money where their mouth is? How long is the warranty?
I don't know how they could even come up with a number like that. To my knowledge there isn't a potting compound in existence that could last that long, maybe they invented the roman concrete of potting compound.
The solid state relays I used have a 1000 year operating time. Sounds insane but it's in the data sheet for it. No moving parts, internal optical isolated. The thing is that if the ECU decides to kill power to the pump (aka: a crash!) You REALLY WANT All pumps turnoff. You would never want a scenario where a fuel pump is feeding a fire! I know people do the Hobbs method and I almost did too,. but instead went a safer and more reliable method. I documented everything here on this forum only. Just trying to help.
On all my of my fuel pump relays, the switch is powered by the factory fuel pump power wire, and the hobbs switch controls the ground. So, if the engine turns off, the pumps turn off, just like factory.
And check out this plot I made from my car (and taken from my fuel pump thread):
Notice how at around 18psi the injectors can need anywhere from 40% duty cycle to 80%+ duty cycle !!!
This is what I meant by using boost only to trigger a pump seems sloppy. You can be off by the actual fuel consumption needed by the engine by 100% !
Duty cycle is function of the time it takes for the engine to complete a cycle (this goes down as RPM goes up) vs dwell time. As rpm goes up, the injectors have a smaller window of time to inject fuel. So a 5ms PW at 3k rpms is lower duty cycle than a 5ms PW at 8k rpm. But its the same amount of fuel...
Originally Posted by google search for an easy example
At 6000 rpm it takes 20 ms for two revolutions. If a fuel injector is activated for 15 ms (the IPW) at 3000 rpm the duty cycle is 37.5% (15 ms/40 ms), or rpm times IPW divided by 1200 equals IDC in percent. If an injector is powered for 15 ms at 6000 rpm, then IDC is 75% (15 ms/20 ms).
IDC is not a value to determine the fuel demand/fuel flow required. All it tells you is when you're out of injector (or pump if you see pressure dropping). IPW tells you the amount of fuel being used.
The big turbo car I have here that makes 860whp, runs two AEM 400LPH 044 style pumps in a surge tank, fed by twin walbro 255's in the stock tank. The 255 run full power full time. We only run one 044 until 18-20psi, then the second pump comes. Works like a charm.
We tried runn just one 255 until 5-10psi, but we found there would be random times the surge tank would go dry, so we wired them up to run full time.
The big turbo car I have here that makes 860whp, runs two AEM 400LPH 044 style pumps in a surge tank, fed by twin walbro 255's in the stock tank. The 255 run full power full time. We only run one 044 until 18-20psi, then the second pump comes. Works like a charm.
We tried runn just one 255 until 5-10psi, but we found there would be random times the surge tank would go dry, so we wired them up to run full time.
I know if it ain't broke don't fix it, but if you wanted to you could install a couple of float switches in the surge tank and use some relays to create a hysteresis so that the 255's will keep the surge tank full but won't have to run non stop.
Aug 7, 2019 | 06:40 PM
