Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 Ahh, you are forgetting a fundamental and necessary part of a supercharged fuel system. The fuel pressure must be referenced to plenum pressure. As boost is created above atmospheric pressure a means must be used to increase FUEL pressure the same amount, as the boost is causing a positive pressure for the injectors to "blow" against. That's the reference port connected (I hope...) by a thin hose to the engine side of the intake system, after the throttle body. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 I simplify slightly, the very modern return-less fuel systems work a bit differently, there is no separate fuel return to the tank, regulation is done *AT* the in tank fuel pump, and I *THINK* supercharged engines are catered for by PWM control of the pump speed. Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 (edited) Ahh, you are forgetting a fundamental and necessary part of a supercharged fuel system. The fuel pressure must be referenced to plenum pressure. As boost is created above atmospheric pressure a means must be used to increase FUEL pressure the same amount, as the boost is causing a positive pressure for the injectors to "blow" against. That's the reference port connected (I hope...) by a thin hose to the engine side of the intake system, after the throttle body. My fuel pressure is measured in the line via a mechanical gauge though? As far as the pump is concerned it should just be on and going for broke. Is that not the reason that modified turbo cars require a higher fuel line pressure than non-turbo cars. And also the reason why the big boys running 3+bar of boost need silly FPR levels? I was a calibrator for a few years and I worked with nothing but pressure transducers etc. This is why I really want to get my head around it as it's really going against my understanding of it all As a side note, we use large pumps for the aviation fuel. The pump motor is on and runs a constant voltage/draw regardless of whether 1 engine is running or 3 engines are running. Once 3 engines are running the second pump switches on to keep the flow rate up. No change in voltage or draw, there is a HUGE return pipe that is connected to the fuel regulators in each cell. In fact, I tell a lie. There is an increase in draw when no engines are running.... as I would expect due to the increased pressure flowing the fuel around the return circuit. Edited February 11, 2015 by Scott (see edit history) Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 The increased current draw under boost is because your rail pressure goes up in direct proportion to the boost the supercharging device is producing. More pressure needs more current to the pump, it has to work harder. You are not thinking about referencing fuel rail pressure to boost pressure.... Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 (edited) The increased current draw under boost is because your rail pressure goes up in direct proportion to the boost the supercharging device is producing. More pressure needs more current to the pump, it has to work harder. You are not thinking about referencing fuel rail pressure to boost pressure.... I understand that mate, as I said. I think we're going round in circles. The increased pressure comes from the FPR closing off the return, not from the pump increasing its rate. Edit: I'm not sure about the stock FPR, but my FPR works by keeping the pressure in the fuel rail at the set value according to atmospheric. If the boost pressure increases to 1bar, are you saying the pressure in the rail increases by 1 bar? Surely if that was the case the mechanical gauge would show an increase of 1bar to it's already set 3 bar? It's my understanding that the FPR works to a direct atmospheric comparison. If the FPR is set to 3 bar, then the pressure in the fuel rail is 3 bar. This is regardless of what back pressure is being created by the boost. If the boost is 1bar, then the FPR keeps the rail running at 3 bar total (2bar fuel, 1 bar boost). As I said earlier, this is the reason for my understanding regarding properly high performance cars needing much higher pressure feeds. They need to have 5bar+ in order to overcome the boost pressure from the intake and still keep the fuel flow pressure high enough to supply enough fuel. Edited February 11, 2015 by Scott (see edit history) Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 (edited) No, supercharged cars reference fuel pressure from the plenum. If you have an X PSI with no boost, then you make the engine create 10 PSI boost, the fuel pressure (should) go to X plus 10 PSI pressure. Before the realm of every car having EFI people used rising rate fuel pressure regulators, where the rail pressure went up more than boost pressure. A cheap and dirty way to get more fuel into the engine as boost increases, on cars that did not originally have a turbo engine and an ecu that would alter injector pulse width to suit boost levels. Bear in mind the plenum also sees a vacuum, so under idling, overrun etcetera the fuel rail pressure is reduced from the baseline pressure you will see if you pull the hose off the top of the regulator. Edited February 11, 2015 by Chris Wilson (see edit history) Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 No, supercharged cars reference fuel pressure from the plenum. If you have an X PSI with no boost, then you make the engine create 10 PSI boost, the fuel pressure (should) go to X plus 10 PSI pressure. Before the realm of every car havin EFI people used rising rate fuel pressure regulators, where the rail pressure went up more than boost pressure. A cheap and dirty way to get more fuel into the engine as boost increases, on cars that did not originally have a turbo engine and an ecu that would alter injector pulse width to suit boost levels. What about the Supra though. I have no reference to my FPR at all. It's adjustment is wholly based on the pressure in the rail on it's own with no reference to the manifold pressure. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 Well something is amiss there. What regulator is it? http://www.turbosmartusa.com/technical-articles/how-does-an-fpr-work/ Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 Well something is amiss there. What regulator is it? http://www.turbosmartusa.com/technical-articles/how-does-an-fpr-work/ And the penny drops. I don't have the reference line connected That explains why the fuel pump would be working harder. Ahhhhh, that's better Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 Here's a photo of my Bosch Motorsport FPR, I consider these the very best available, although it doesn't look trick, they are fabulous, ultra reliable regulators. The top nipple is for the vac /pressure reference line. The stock regulator has a reference line. I have never seen a FPR for a supercharged engine of the 2JZ era that DOESN'T have a reference port! Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 Here's a photo of my Bosch Motorsport FPR, I consider these the very best available, although it doesn't look trick, they are fabulous, ultra reliable regulators. The top nipple is for the vac /pressure reference line. The stock regulator has a reference line. I have never seen a FPR for a supercharged engine of the 2JZ era that DOESN'T have a reference port! Yeah I've just skipped the last step of fitting the bloody thing. Mine does have a reference port also, I completely overlooked it. I'll need to get that hooked up tomorrow. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 Ahhh, if nothing else this thread may well have saved an engine Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 Ahhh, if nothing else this thread may well have saved an engine Indeed, very glad I extended the discussion now. I absolutely hate not understanding something Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted February 11, 2015 Share Posted February 11, 2015 If the boost pressure increases to 1bar, are you saying the pressure in the rail increases by 1 bar? Surely if that was the case the mechanical gauge would show an increase of 1bar to it's already set 3 bar? Yes! What is key in EFI applications without fuel pressure feedback to the ECU is to have a constant *differential* pressure across the injectors to keep the average flow rate for a given injector pulsewidth constant. When we say we set the fuel pressure to 3 bar, we're saying that the pressure in the input end of the injector, minus the pressure at the output end of the injector is 3 bar. The fuel pressure is normally set with the engine not running, so the output side of the injector is at atmospheric pressure. 3 bars (input) - 0 bars (output) = 3 bars (differential). A pressure gauge is also giving a differential reading relative to atmospheric pressure so it will indicate 3 bars. When the engine is started it draws a vacuum in the intake (and therefore at the output of the injectors) of e.g. -0.5 bars, results may vary. In this case we still want a differential pressure of 3 bars, the FPR will drop the absolute rail pressure to 2.5 bars (gauge). 2.5 bars - (-0.5 bars) = 3 bars. You can verify this by watching a gauge connected to a fuel rail with the engine stopped (but pump running) and then with the engine idling. In exactly the same way, when boosting to e.g. 1.5 bars, the pressure at the output of the injectors is 1.5 bars (gauge) so the FPR will move the rail pressure to 4.5 bars to keep the differential pressure to 3 bars. 4 bars - 1.5 bars = 3 bars. Quote Link to comment Share on other sites More sharing options...
Scott Posted February 11, 2015 Share Posted February 11, 2015 Yes! What is key in EFI applications without fuel pressure feedback to the ECU is to have a constant *differential* pressure across the injectors to keep the average flow rate for a given injector pulsewidth constant. When we say we set the fuel pressure to 3 bar, we're saying that the pressure in the input end of the injector, minus the pressure at the output end of the injector is 3 bar. The fuel pressure is normally set with the engine not running, so the output side of the injector is at atmospheric pressure. 3 bars (input) - 0 bars (output) = 3 bars (differential). A pressure gauge is also giving a differential reading relative to atmospheric pressure so it will indicate 3 bars. When the engine is started it draws a vacuum in the intake (and therefore at the output of the injectors) of e.g. -0.5 bars, results may vary. In this case we still want a differential pressure of 3 bars, the FPR will drop the absolute rail pressure to 2.5 bars (gauge). 2.5 bars - (-0.5 bars) = 3 bars. You can verify this by watching a gauge connected to a fuel rail with the engine stopped (but pump running) and then with the engine idling. In exactly the same way, when boosting to e.g. 1.5 bars, the pressure at the output of the injectors is 1.5 bars (gauge) so the FPR will move the rail pressure to 4.5 bars to keep the differential pressure to 3 bars. 4 bars - 1.5 bars = 3 bars. All makes perfect sense now. I'm sure I'll now notice it when I attach the reference line Quote Link to comment Share on other sites More sharing options...
heckler Posted February 11, 2015 Share Posted February 11, 2015 when I fitted my 044 - i used all mil spec, plus aircraft grade cable rated at 60+ Amps - slightly overkill, but that what I had at the time! Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted February 11, 2015 Author Share Posted February 11, 2015 when I fitted my 044 - i used all mil spec, plus aircraft grade cable rated at 60+ Amps - slightly overkill, but that what I had at the time! If only I could get the taxpayer to fund my Supra build too Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 If only I could get the taxpayer to fund my Supra build too How's the new scratching post by the way, good? I have noted thet riposte, I like it..... Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted February 11, 2015 Author Share Posted February 11, 2015 My new fuel pump circuit should look like this, correct? Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 (edited) Looks OK to me, but I think a 15 amp fuse would be plenty. If you are binning the fuel pump ecu you could take the relay coil feed from the stock ecu side of the wires to it. I guess you are feeding it from a none stock ecu though? Edited February 11, 2015 by Chris Wilson (see edit history) Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted February 11, 2015 Author Share Posted February 11, 2015 Looks OK to me, but I think a 15 amp fuse would be plenty. If you are binning the fuel pump ecu you could take the relay coil feed from the stock ecu side of the wires to it. I guess you are feeding it from a none stock ecu though? It's BPU on a factory VVTi/Tiptronic management for now. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 Are you bypassing the stock fuel pump ecu in the LH rear 1/4 panel though? If not the relay solenoid coil will see varying voltages. Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted February 11, 2015 Author Share Posted February 11, 2015 (edited) As in running the fuel pump permanently on 12v rather than 9v on the low setting? Or the '12v fuel pump mod' as the Yanks call it? Edited February 11, 2015 by j_jza80 (see edit history) Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 11, 2015 Share Posted February 11, 2015 What I am saying is if you take the existing fuel pump feed wires at the tank top connector and use them to energise your relay, that relay coil will see whatever volts the stock fuel pump ecu in the rear quatr panel decides to output. Sometimes 12V, sometimes less, maybe little enough for the relay to stop closing its contacts. I am not convinced the stock pump ecu does just output 12V or 9V, I suspect it's more subtle than that and may have a sliding voltage, maybe pulse width modulated. there's a lot going on inside one, electrically, lots of components! I'd bypass the fuel ecu and run the wire to the new relay from the stock wire to the input side of the fuel pump ecu. I think that's possible. Where's Andy..... ? I am not sure the stock fuel pump ecu would be happy with the extra current draw of an 044. If it was, and you wanted to keep the multi voltage set up to the pump, you don't need that relay. Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted February 11, 2015 Author Share Posted February 11, 2015 I should be able to find the wire into the fuel pump ecu easily enough, as the permanent 12v mod (fuelpump ecu bypass) requires joining the two thickest wires together. So with the key in, one *should* read 12v, one lower (9v?) It seems a shame to undo all of Toyota's hard work, but I guess they didn't have Bosch 044 pumps in mind when designing the JZA80 Quote Link to comment Share on other sites More sharing options...
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