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Discussion Starter #1 (Edited)
A while back I put a fuel pump in my red car.. And as I wanted to make room for future upgrades, I opted for a supra pump.

Now being as I was too smart (alternately read as stupid) to actually use the search function, my brilliant plan was to duplicate the stock system, and run the resistor at low speeds, and the hotwire at high load... (many of you will recognize this as the Erik Gross method, but in reference to the above search impairment, I had never heard of it..) So I basically got to find out the hard way that supra pumps don't like that... I had the predictable hesitation and flat spot before the transition. I went ahead and hotwired it full time to see if I could get away with it, but expected to have issues with overruning the FPR... I actually thought I got away with it for a while, but in the process of fixing some other issues with the car (bad O2s) It became clear that something else just wasn't right... So this weekend, I put a fuel pressure gauge on it, and discovered that it was in fact running right over the top of the FPR..

So what to do....? the obvious choice is an aftermarket FPR, but I want to fix it today. And spending that kind of money on this car is just money that I can't spend getting the white car running... I'm also kinda bent that my plan with the resistor didn't work. I want to know why...? So out comes the lab scope, we're going to find out whats going on here...

First test was hotwired full speed: The pump was pulling 15 amps and turning 7500rpm, and running right over the FPR.



Second test, through the resistor: the amperage dropped in half down to 7.5, and the pump was lumbering along at 3500rpm... At that speed, it couldn't muster 50psi deadheaded...(no wonder it had a hesitation, it couldn't feed a good running Hyundai at that rate..) I also had the added benefit of the resistor doing double duty as a shop heater at this point...



So I started to think that maybe the method isn't bad, but the stock resistor is just too much for that pump... My theory was that if I could cut the resistance in half, I could get the pump speed up around 5000 rpm, and life would be good again.. So how do you accomplish such a task....?




So on to test #3, through the new double resistor: 10amps, 5000 rpm, 80+ psi deadheaded, and no FPR overrun... :yay:



I still have some testing to do... When I left the shop tonight the fog was way to thick to even think about making any pulls, but so far it appears to be a complete success... No more blubbering, hesitations, or any other signs of poor fuel control. The couple times I did have room to get after it a little in lower gears it pulled hard and smooth... I'm extremely happy with the way the car runs now. :bigthumb:
 

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Signing on-----interesting thread, thanks for your time testing this theory. I plan to install a Denso pump in my 1996 VR-4 so it would be helpful to know if your idea works. Thanks again, Ray
 

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Re: You guys will love this one... (pump, fuel pressure)

Interesting ! Some short questions :

- Have you measured and maybe recorded the voltage at the pump vs engine rpm?
- by "running right over the top of the FPR" do you mean that with the Supra pump and hotwiring the FP rised over normal?
- Where exactly have you measured the current?
- How did you measure the pump speed (rpm) ? Is this the ripple-frequency in the measured signal?

I don't understand why the supra pumps aren't happy with the stock resistor. Many of us have installed a Supra pump without problems. In my cars I do not have the hotwiring methods as the voltages are still fine at the pump.
 

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Discussion Starter #4
Re: You guys will love this one... (pump, fuel pressure)

Interesting ! Some short questions :

- Have you measured and maybe recorded the voltage at the pump vs engine rpm?
- by "running right over the top of the FPR" do you mean that with the Supra pump and hotwiring the FP rised over normal?
- Where exactly have you measured the current?
- How did you measure the pump speed (rpm) ? Is this the ripple-frequency in the measured signal?

I don't understand why the supra pumps aren't happy with the stock resistor. Many of us have installed a Supra pump without problems. In my cars I do not have the hotwiring methods as the voltages are still fine at the pump.
1: no I haven't, I did measure the voltage at the output of the relay when I was doing my initial testing... (done with engine off, battery charger maintaining 13.6 volts) obviously I had battery voltage in hotwire mode, and IIRC, I was only dropping about 1/2 volt through my hotwire when I checked it a few months ago, so we can assume that I had real close to 13 at the pump. Through the resistor I was only getting a little over seven volts, so we can assume it was equally as dismal if not a little worse at the pump.

2: Yes, it was running 48+ psi at zero vacuum, and no amount of vacuum would get it under 44.

3: Current was measured with an inductive amp probe clamped around the fuel pump wire.

4:Yes, the ripples you see in the waveform is the current change as the armature passes the brushes. If you know the number of armature elements(in this case 12) you can look at the waveform to determine how many milliseconds it takes to make one revolution. Divide that number into one minute(60K milliseconds) and you get the RPM of the motor.

Have you done a resistor bypass on yours? Stories like yours confuse me as well, I have to wonder if some of these pumps are designed differently than others. I would love to have access to a few more to test, but I'm pretty secluded from most of the community. I do know that mine is a HUGE power hog... 15amps is a lot of power for a fuel pump, and it obviously wasn't going for the resistor. If I tried to run this thing off of the stock wiring, I'd half expect to have a new footwarmer for my passenger...

My fuel pump system currently is completely self contained, and does not use any power from the stock wiring even in resisted mode... It's all built from heavy gauge wire and 40 amp relays. (It was actually easier to do it that way without totally hacking the stock wiring) I'll try to build a better diagram when I have time, but here's a pic of my scribbles as I was building it:



And yes I do have a 30 amp inline fuse in the battery feed, it's just not in the scribble.... :D
 

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Thanks a alot for your great answers. Helps a lot for further problem analysis on others.

I've installed a Supra pump in my daily driver a few months ago and have not seen any different behaviour than with the stock pump on the stock fuel and stock wiring system. Nothing is bypassed so I did not expect any change at idle or rpms below 3000rpm. The most difference is that the power doesn't decrease above 6200 rpm anymore and that the new pump is more noisier than before.

Due to the diagrams from the Denso flow tests the Supra pumps flows 110 l/h more @43 psi FP than the stock pump (no resistor, full voltage to the pump). Now the question is, does FP rise or does the flow rise. 110 l/h are just 1.83 l/min what the stock FPR easily can handle to return to the tank. Having the resistor inline even lowers that figure to around 60l/h. Also this can easily be handled by the stock regulator.

But the regulator doesn't know anything about flow or pressure as it just changes the pressure linear to the vacuum/boost situation. Therefore pressure simply must rise. Therefore the ECU adapts the IDC to the new "richer" conditions while FP indeed is above the desired 43 psi. Am I wrong ?

Not any data like you have (I can't find the inductive clamp after the move ...) so far. The 285l/h pump I have from Denso is rated up to 21 Amp. This may be the max the pump is drawing if the fuel lines may be blocked.
 

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the 3S whisperer
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ive had a denso for years without issue i hope i have it hooked up right. ill have to compare . i think i did the rdr method, is that right?
 

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Discussion Starter #7
ive had a denso for years without issue i hope i have it hooked up right. ill have to compare . i think i did the rdr method, is that right?
If I'm not mistaken, you have an aftermarket fuel pressure regulator don't you? If that's the case, you don't have to worry about the fuel pump overpowering it, so you should just feed it as much power as possible and let it fly...
 

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I measured Fuel Pressure on the stock fuel and wiring system and nothing changed after the installation of a Supra pump. I mailed with the pros and we came to the conclution that a rising fuel pressure with another pump must be caused by a restriction in the return line. An example is the Supras that have a small restriction that always gonna be removed if a larger pump is installed.

In short: There is something different with RealMcCoys fuel system what caused the fuel pressure to rise after the pump upgrade. The mod of the resistors in parallel delivers about 10V instead of 7V below 3000rpm and under low load. This works on any car but is not necessary at all if everything is fine in the fuel system.
 

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This gets more interesting by the day. I hope this last post is correct and then installing a Supra pump will not affect our cars negatively. Although the high demand of the pump may still impact idle vs full throttle? Thanks to all of you who are actively checking these electrical problems.
 

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Discussion Starter #16
I measured Fuel Pressure on the stock fuel and wiring system and nothing changed after the installation of a Supra pump. I mailed with the pros and we came to the conclution that a rising fuel pressure with another pump must be caused by a restriction in the return line. An example is the Supras that have a small restriction that always gonna be removed if a larger pump is installed.

In short: There is something different with RealMcCoys fuel system what caused the fuel pressure to rise after the pump upgrade. The mod of the resistors in parallel delivers about 10V instead of 7V below 3000rpm and under low load. This works on any car but is not necessary at all if everything is fine in the fuel system.
I have to disagree... It's been pretty well documented that when the FPR gets overrun by a larger than stock pump, that the regulator itself is the restriction. The installation of an aftermarket unit fixes the problem... This would not be possible if the line were restricted.

The real difference between your car and mine is the voltage at the pump... The stock wiring cannot deliver over 13 volts to the pump even if the resistor is bypassed... You don't have to deal with the overrun problem because you don't have a 10 gauge wire running straight from your positive battery post to the fuel pump at idle.

The problem that inspired this fix was created when I tried to go BACK to the STOCK resistor to slow the pump down... So the real question is: Why does your supra pump work fine at lower voltages, and mine almost stalled out at 7volts..

I would really love to be able to check voltage, current, and pump speed on your car at slow speed...
 

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Skeptic
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Discussion Starter #19
I was looking through the above link, and found something I'd been previously been looking for... It's Erik's documentation of the issues he had with the supra pump using his now legendary method..

1995 3000GT VR-4: AEM Adjustable Fuel Pressure Regulator

The symptoms he described are exactly what I was experiencing... And his theory as to why it was happening? I proved him right... The supra pump could not deliver at the low voltage.

If you compare the numbers to the stock system, (which on my car was 11 volts non-resisted, 8.5 volts resisted) the resistor dropped the voltage about 30%... On my hotwire system, the resistor was dropping the voltage 50%, and obviously dropping the pump out of it's operating range, with a huge jolt to the system when the pump would suddenly double it's speed. My double resistor put me back closer to a 30% drop, With a 2500 rpm change in pump speed... Basically the same behavior as the stock system... (on steroids)
 

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Honestly, it is not possible that the resistor increased its resistance somehow to lower the current that much. With the resistor the current will be limited. If the voltage increases then also the current goes up (ohm's law).

If we draw a schematic wiring then we would get the motor (a resistor too), the wiring to the pump (another resistor) and the fuel pump resistor. With the stock system you measured 11V at the pump with 12A draw what results in an inductive resistance of 0.92 ohm for the pump. Therefore you loose 2.6V (with gen voltage of 13.6V) through the stock wiring. With 12A current this results in a wiring resistance of 0.22 Ohm. Now we assume that the pump resistor doesn't change the wirings resistance. With it in-line the voltage at the pump dropped to 8.5V what results in 9.2 Amps draw. With 9.2A the wiring loss drops to 2.0V what results in 4.1V drop through the pump resistor. This leads us to 0.45 Ohms for the pump resistor. Sorry if it sounds complicated but I never had it to expalin in another language ;)

With hotwiring, let's assume that we see 13V over the pump what results in 14A draw. The new wiring only drops 0.6V what results in 0.04 ohms. The pump resistor is still the same. If it is switched inline, the total resistance is 1.41 Ohm what results in 9.6A. With this you should measure 8.8V over the pump. This is more Voltage than you had with the stock wiring.

Therefore the Supra pump will not have any problem with that and the fact that you lost more voltage than before the hotwiring (with the resistor inline)there must be a problem somewhere with the installation and has nothing to do with the pump.

I've read many instructions of the rewiring including Eric's ones and do not find a problem in the principle at all. But the whole system may be very sensitive to connectors and corroded contacts too (especially the relais).

Good thread, hope we can solve any issue related to pumps and hotwiring.
 
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