Attention! Alternatorless modders. Get your voltage up - Page 4 - Fuel Economy, Hypermiling, EcoModding News and Forum

Christ · 06-18-2009, 05:44 PM

Pressure regulation on most cars is mechanical, but when running at lower voltages, the speed of the pump isn't correct, and thus it can't produce the normal range of pressures that it should be.

Daox · 06-18-2009, 05:49 PM

True, but you only need max pump flow at peak rpms & peak loads. An ecodriver shouldn't have any problems. Plus, pumps are oversized to begin with.

Christ · 06-18-2009, 05:58 PM

I wasn't talking about pump flow. You need a constant pressure, regardless of flow rates.

If you can't keep the correct voltage to the pump, you won't get the correct pressure, and you'll have less vaporization and your injectors will have to run longer to get the right amount of fuel into the engine.

To test this, Run your fuel pump at 6VDC, then 8VDC, then 10VDC, then 12VDC, then 14.4VDC, and record the pressure at the fuel rail for each voltage. As you increase voltage, rail pressure will increase as well.

The pump runs on variable timing, not variable electrical input. This means that it may click on and off 100 times a minute (on a non-return system) to supply the correct amount of fuel at the correct pressure. On a return system, it runs constantly at the specified voltage (100% duty cycle) and the regulator/return valve keeps the pressure and flow rates under control.

A simple mod when you're getting too much fuel is just to turn down the rail pressure. You normally do this by modding the pressure regulator, but on non-return vehicles, you hotwire the pump and control the voltage with an electrical circuit.

Daox · 06-18-2009, 06:06 PM

I'll have to take your word for it. I thought that non-return vehicles used the same sort of pressure regulator (except in the tank) as return type vehicles do. Testing pressures at different voltages would be interesting, but I don't have a fuel pressure gauge I can just plug in.

I'd be very interested in any info anyone has on how much power the ignition coil and fuel pump require. I suspect its not a tiny amount.

Christ · 06-18-2009, 07:30 PM

Quote:

Originally Posted by Daox

I'll have to take your word for it. I thought that non-return vehicles used the same sort of pressure regulator (except in the tank) as return type vehicles do. Testing pressures at different voltages would be interesting, but I don't have a fuel pressure gauge I can just plug in.

I'd be very interested in any info anyone has on how much power the ignition coil and fuel pump require. I suspect its not a tiny amount.

Actually, you may be correct on the in-tank regulator thing... I've only seen mention of varied voltage controlling pressure, never seen it in practice... but I've also never had to really work on a returnless fuel system, either.

I'll do some research for a few mins, and see what I come up with.

Christ · 06-18-2009, 07:34 PM

Quote:

A returnless fuel injection system, by comparison, manages fuel pressure a little differently. Instead of using a spring-loaded vacuum diaphragm in the regulator to change fuel delivery when throttle opening and intake vacuum change, the regulator in a returnless system operates at a constant pressure. The older return-type systems need to vary fuel pressure to maintain the same pressure differential across the injectors when intake vacuum drops. When vacuum drops, the regulator increases pressure to compensate. But in a returnless system, this isn't necessary because the line pressure is always the same.

So how does the system compensate for changes in engine load and vacuum? A returnless system uses the Powertrain Control Module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted on the supply rail allows the PCM to monitor fuel pressure. When pressure in the supply rail drops as engine load or speed increase, the PCM compensates by increasing injector duration (on time) and/or the operating speed of the fuel pump.

Some systems (Ford, for example), vary the fuel pump's output by changing the voltage supply to the fuel pump module. When more fuel is needed, pump speed is increased by increasing the pulse-width (on-time) of the pump's voltage signal (pulse-width modulation).

From Diagnosing Returnless Fuel Injection Systems

So it could be done both ways, actually. One way is to keep constant pressure, but vary pulse-width of the injectors, the other way is to use variable voltage supply.

orange4boy · 06-19-2009, 04:34 PM

Thank Christ!

I was wondering about the fuel pressure situation. So depending on the vehicle, low voltage could cause problems or not, but most likely will.

If the injectors are open longer to compensate for lower pressure this would throw off the mpguino because the micro gallons per second would be different than at higher pressure right? This would explain my sudden high mileage numbers when I went from 12V to 18V. Not so much the injector delay.

I wonder how much vaporization is improved at higher pressure? Seems to me a lot from my experience with spray finishing. HVLP - big, slow droplets, conventional 40psi - light fast fog.

Thanks for the info.

Daox, on my van, 2.4L 4cyl the running amp draw is about 15 with everything else off but I noticed it goes up to 20 under hard acceleration (probably the fuel pump). Some of the total is running lights though. I think a 25A dc-dc would do the job.

I just set up mine with one 12V series 27 deep cycle and one 6V Trojan in series to get 18V. They have to be charged separately though. That is one way to save pounds and space. You could tap the 12v to run the stuff that does not care and tap the 18 for the fuel pump and coil. I may just do this at some point since the 18v fries my headlights instantly. I suppose you could find a small 6 volt battery used for certain classic cars somewhere which would match the capacity of your current battery.

Daox · 06-19-2009, 04:49 PM

Great info Christ. So, I guess now we just have to find a DC to DC converter for the fuel pump and ignition coil. This might be a bit trickier. I've looked around for higher amperage DC to DC converters, and I haven't found anything.