So I've recently put a fuel pressure gauge in and a Walbro 485 pump in a while ago. The readings from the gauge are about 49ish psi idle and 61ish psi at full boost (9 psi). This is much higher than what the service manual says it should be (around 36 psi idle). Is this an issue? Does it matter that it's so high? Also, I'm pretty sure that it's the pump causing it but I'm not 100% sure. Is this something an aftermarket pump would cause?
Regualtor and returnline overrun. Pump pumps more fuel than the regualtor and returnline can bleed off. So the pressure rises. Running the stock fuelpump controller or straight battery power to the pump?
I'm fairly sure it's using the stock pump controller. I used the same wires going to the stock pump and just soldered on the new connector. No. Should I be? I suppose it's kinda what I'm trying to find out.
The fuel pump doesn't create fuel pressure. It's the resistance to fuel flow that creates fuel pressure. Are you sure the pressure gauge is reading correctly?
If you're running a higher spec pump yes you should be. You can then adjust fuel pressure accordingly.
Honestly? Unsure. I'll grab a friends and whack it in and see what it all says. Any recommendations for a good aftermarket fuel reg?
Something from theese guys should do http://fuelab.com/products/performance/fuel-pressure-regulators/
Should be able to do you a good deal on a Turbosmart -shoot me a PM with the specs on your fuel system if you'd like a quote
I wouldn't expect pressure to keep climbing as it makes boost if the reg was the issue, I could be wrong though and you should have a larger reg with the 485. What does it do at idle if you disconnect the vac line? Is the pump still running off the fuel computer?
Actually the DIFFERENTIAL fuelpressure (relation between railpressure and manifold pressure. Should stay as close to the set pressure (43.5 psi) all the time) will first drop down until the injectors are able to bleed of enough fuel so that the regulator can do its job again. And not be overrun by the pump. From here on the DFP will stay at its set value. Until you get into the zone where your feedlines are to thin or your pump looses omph. Then the DFP will drop under the base setting.
Yeah, that's basically what I was thinking, if it [gauge pressure] rises as manifold pressure increases then the reg is control of fuel pressure right? Unless the pump is speeding up.
Im back... This is a log of my own car. I have an Aeromotive a1000 regulator on it. 300* rail, Nismo 740`s. Stock feed line up to the stock fuelfilter and stock returnline from the regulator. I have one 485 pump regualate via PWM and a 255 pump coming on via a regular relay. My base fuelpressure as set at idle, Vacuumline disconnected and 485 pump running at 35% dutycycle is 310 kpa. That should cover it i think.. Now, as pr graph before i mash the throttle my DFP (differential fuel pressure) sits at 310 kpa. I am cruising at this point Fuel pressure is at 270 kpa. Boost is representated as "efficiency calculation" in my setup. Its boosting up to 260 kpa in this log. When i mash the throttle you can see that the fuelpressure is climbing. However the DPF is dropping all the way to 280 when i let go of the throttle. This is because of my stock feedlines. They cant flow enough to keep the pressure up. This is something i know of and it is consistent and possible to tune around. Also sinse i have a propper ecu it is compensating for my fuelpressure as can be seen at the white bottom graph. You can also see where my second pump comes on and off in that section. Now this grapf is what is should look like (exept the dropping DFP) and you can see that fuelpressure can still climb even though DFP drops! Whe i let go of the throttle my DFP climbes to 320kpa instead of 310 because pump is still running but my injectors are closed... Next graph! Here i have the 485 pump at full tilt at the marker. You can also see where pump 2 comes in. This is a log i made a while ago for demonstration. This run in my low power map and it was only at 180kpa (0.8 bar) boost so not completly comparable to the other graph. At the marker DFP is 331 kpa. it have rised 20 kpa compared to the other log. This is because pump is overrunning my returnlines and possibly my aeromotive regulator. Where i let go of the throttle DFP is 300 kpa and fuel pressure is 379. Also at this log you can see that raw fuelpressure does NOT drop of at all. But my DFP is. DFP should really stay a flat line when all is up to par. And again my FP compensation is here to save the day so my afr`s stay where they should. Ignore my lambda values. Both my sensors were stuffed at those logs. All this is with my Aeromotive regulator. Imagine it with the stock regulator instead.
So I think I followed that. The fuel pressure is rising because the line is too small for the extra fuel being pumped by the aftermarket pump and the stock reg can't cope? So to fix it I just need an aftermarket fuel reg to replace the stock one?
So I replace the reg and then use that to adjust fuel pressure back to what it should be stock? Besides from the pump my fuel system is completely stock at the moment. Could nistune be used to regulate pump speed?
Yeah, reg will be a straight swap. Make sure when you set it you do it with the vacuum line disconnected from the reg and set it to the stock 43.5psi under those conditions, then just make sure it drops once the line is connected and it's idling. I'm pretty sure the 485 pumps aren't variable speed, some pumps can be controlled by the ECU but those walbros don't work properly without full voltage.
Can that be done through nistune or do I need to construct a pump speed controller that runs pwm to the pump? I'm assuming as well that if I used pwm I'd need to upgrade the fuel damper as well?
