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Old 07-17-2019, 09:41 PM
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krisr krisr is offline
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Default Street car, E85, PWM the fuel pump

Heya boosty/EFI guys, thought i'd share an experience that i'd been working through lately with my car as i've recently switched to E85 to see if I can squeeze a bit more out of my 400 in the quest for 10's.

Since going to E85, my in tank swirl pot/pump/regulator/all-in-one unit seems to have a couple of issues with delivery now as WOT it's using about 60-65% more than pump gas, so there's a lot more demand on the pump. When I took it to a car show where they let us do happy laps on a race track on the main straight I emptied the pot within about 3 seconds so there was zero chance of this working. Ultimately i'm going back to a fuel cell, but that'll be a bit later on when I save up a few $$$.

In the mean time I thought i'd try a pump setup from a later model car VERY similar to the ZL1 Camaro fuel modules, managed to modify the inside secondary pickup by pressing new quick connect fittings onto the OE nylon fuel line and made up a new nylon line to adapt to the existing line in the car with -8 fittings, also made a new patch harness to the body wiring. One thing that got me was when I gave it full +12V, I had 85psi of fuel pressure - WTF?!

After a bit of reading on these later model cars and their fuel systems, it turns out that cars from 2000 onward started to use fuel pump controllers, where they take a pulsewidth signal from the ECU to control the pump speed. I tested the theory with a solid state relay at 100hz and sure enough, pump pressure came down to 60psi which is what I told the ECU to run! But at 100hz the pump makes a very audible hum. The controllers they use step up the frequency from the 100hz input to like 20kHz to the DC motor you're going to control which makes them silent.

Long story short, after a lot of digging around at various controller spec sheets, I found that the controller from late model Jaguars seem to be the best ones and the most reliable. My Jag sources tell me they're a Siemens unit and not a Lucas and the settings needed in the ECU to drive it tell me it shares a lot of the electronics with the Ford FPDM. Jag owners have also never heard of a controller failing so i'm pretty confident it'll be reliable. There's also a place in New Zealand called NZEFI which also sells refurbished units that come with nice CNC cut mounting brackets and a plug ready to be crimped so no need to solder anything.

So after redoing the wiring for the controller, I set the ECU to an inverted 100hz signal, minimum duty of 5% and a maximum duty of 50% as higher or lower puts the controller into a shutoff/fault mode and voila! We now have full pump control! The thing I like about this most is that i'm only running the pump at about 28% duty (effectively 56% at the pump) so it's not doing much work at all to maintain 60psi but as you get a little bit more spirited the logs show the duty raise as needed to keep the pressure consistent - this is running closed loop against a fuel pressure sensor. I also need 60psi to ensure that the syphon jet inside the pump functions to keep the bucket full.

You can see from the log, the fuel pressure and duty traces are always adjusting/trimming to keep the FP as constant as possible which in turn is using a LOT less current to drive the pump and by doing this, you can use really big pumps and injectors on street cars quite easily as you can drop the fuel pressure at idle/cruise so you can get a reasonable injector PW etc...

In short, PWM is a good thing!

Kris
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  #2  
Old 07-17-2019, 10:26 PM
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I thought about the switch to e85, I would need another pump also. I am blow thru now, so I figured I will wait till I can afford f.i. and make the change all at one time. Keep us posted when you get it worked out on how much you picked up.
Thanks for the info!

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Old 07-17-2019, 10:57 PM
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Quote:
Originally Posted by JSPONT View Post
I thought about the switch to e85, I would need another pump also. I am blow thru now, so I figured I will wait till I can afford f.i. and make the change all at one time. Keep us posted when you get it worked out on how much you picked up.
Thanks for the info!
Yeah my plan with the cell is to run a twin in-tank pump assembly and stage them so the controller will control a DW300 pump and if fuel pressure drops whilst having a bit of a spirited drive above 4000rpm if the primary cannot keep, then just switch on pump #2. Never had this issue with pump gas, but I was warned when I started to look at E85, make sure your supply is at least double than what you need for pump gas. So far they're not lying

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Old 07-18-2019, 03:04 PM
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Good fuel pumps are not cheap either!! So to convert, to e85 with the blow thru still about a $1000.00 us

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Old 07-18-2019, 03:40 PM
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One thing to also keep in mind is the pump itself. A lot of the older style large pumps were never designed to be dead headed and run PWM. While they will do it, they tend to burn out in short order. Going the PWM with control route, I would highly suggest using any of the numerous OEM pumps available. Whatever they're using in the ZL1, ZR1, Hellcat, GT500 etc. is going to be a good choice. Stack as many as you need for your fuel requirements.

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Old 07-18-2019, 06:55 PM
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I always run a return line.

I was thinking about meth injection with pump gas. I had a 89 TTA (the v6 turbo cars) I was running 26 psi on pump gas with meth injection. It was one Julio from Alky control kit.

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Old 07-18-2019, 07:23 PM
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Quote:
Originally Posted by JLMounce View Post
One thing to also keep in mind is the pump itself. A lot of the older style large pumps were never designed to be dead headed and run PWM. While they will do it, they tend to burn out in short order. Going the PWM with control route, I would highly suggest using any of the numerous OEM pumps available. Whatever they're using in the ZL1, ZR1, Hellcat, GT500 etc. is going to be a good choice. Stack as many as you need for your fuel requirements.
I think what kills them is one of 2 things, 1) if you use the wrong frequency you can hammer the bearings/bushes and eventually kill the brushes. 100Hz is way to slow for a brush motor but these controllers step it right up to 10-20kHz which makes them virtually silent and/or 2) if you try and control the speed using voltage control that puts more load on it, but if the controller is a true PWM 0-12v they should last a very long time. The controller is the key to it from what most electro folk tell me and to stay away from voltage control unless the motor can handle it.

Was testing a solid state relay the other day on a radiator cooling fan and at 100Hz it sounded like a jack hammer was hitting it, but at 20kHz it was dead quiet and smooth to ramp up/down which a lot of new cars use now too. Another thing to experiment with later I guess.

I still plan to use a return style regulator as a failsafe should anything go wrong but just set at 70psi but time will tell when I get the Deatschworks pumps setup in the new tank. The idea is more aimed around being able to run very large pumps in the realm of 300-450lph which are very big for a street car on pump gas, but are a good size for an ethanol/flex fuel car and not having to deal with 15-18A running into the fuel tank continuously when you only need 7-8A most of the time. Same thing with the injectors, I plan to upgrade to ID1000's later on as i'm nearly maxing out my 660cc's on ethanol, but to avoid idle issues I can run a lower fuel pressure to run a reasonable injector PW at idle/cruise.

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Last edited by krisr; 07-18-2019 at 07:30 PM.
  #8  
Old 07-18-2019, 09:05 PM
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A lot of good info here.

Tom V.

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Old 07-18-2019, 10:05 PM
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Good work Kris. Keep us updated on the performance improvements from E85.

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