Vaporworx / Rick's Tank Problem - dropping fuel pressure at high rpm?

[carbuff]

Tonight while running through some datalogs from my tuning runs this afternoon I noticed something strange. My fuel pressure at the fuel rails is dropping at mid-to-high RPM. I did not expect to see that, so I'm wondering if this would be considered 'normal' or not.

I have a Rick's Tank with the vaporworx setup, with the (I think) 5th Gen fuel pump / regulator as purchased from Rick's. I'm running a combination of -6AN and 3/8" hardline from the tank to my fuel rails, and my pressure sensor is at the dead-head end of the rail. I'm running a set of 39 lb/hr injectors on the engine.

You can see in the plot below that the AFR as measured is pretty stable, so perhaps my ECU has already 'tuned in' the drop in pressure. But I was surprised to see a 6# drop.

Has anyone else noticed this with the same pump / tank setup? Anyone else surprised by this?

BTW, I only noticed this because, of all things, my ignition timing dropped way down at this time, and I couldn't figure out why. I then realized that the Holley HP EFI setup I have was pulling timing (as I have it set up to do) when the fuel pressure dropped below 53psi. So at least I 'tested' out that functionality... ;)

[CarlC]

Sorry I missed this thread Bryan.

Any mechanical regulator that is not manifold referenced will lose fuel pressure as the fuel volume to the engine increases. That 6psi drop is about the maximum that will be seen before all of the fuel goes to the engine instead of being bypassed in the fuel module. The C5 Corvette fuel filter/regulator has the same performance properties as well.

In other words, what you are seeing is normal for that regulator setup. With your 39lb/hr injectors, theoretical 100% duty cycle means 312lb/hr of fuel. The LS3 pump @ 55psi can supply 313lbs/hr @ 13.5volts.

There is another regulator available that will not have as much pressure drop. It's a Delphi FP10075, but the initial fuel pressure will be a bit higher (61-62psi) but only drop about 3psi.

[carbuff]

Carl,

I appreciate the reply. I collected some more data on another set of runs yesterday, and I actually saw a scenario where the pressure dropped to 45 psi. I will try to post of a screenshot later, but I confirmed that the voltage in the system (at least as measured at the ECU) was steady, so it wasn't a voltage drop.

Currently I'm not running your pwm control module, although as I have re-read the threads about them, I'm thinking that may be what I want/need. I presume that system is more capable of stabilizing the pressure, given that is measures the pressure near the outlet of the pump? Obviously that's only true up to the limits of the pump's flow rate, but it seems like, while close, my HP levels should be sustainable with the Gen5 pump.

I'm getting educated on the capabilities of the pump and system, so I appreciate the help here! I didn't think I was that close to the 'edge' on the pump's performance, but it seems I am close. Interestingly, even with the drop in pressure, I've noted that my ECU is able to maintain the targetted AFR ratios. I likely have those a bit on the rich side at this point, since I'm still tuning, and that may be exasperating the problem. But it's not THAT rich.

Thanx!

[carbuff]

Carl,

Here is the run where I saw the drop to 44psi.



Hopefully you can read that. It was interesting to me on that run that the pressure starting to drop before I was even at 50% throttle. But also, as I said in the last post, you can see that the AFR actually holds where the ECU is targeting.

I'm definitely still new to tuning with the Holley ECU, but another thing I found interesting about this is that the Injector pulse width doesn't change much at all as the RPMs increase. It seems to go to max opening (however it determines that) and stays there. In 3rd gear, for example, on that chart, it was between 15 and 16 mSec.

[CarlC]

For that injector size the pump should be sufficient. I wonder if the regulator is partially dislodged and making an internal leak. How much horsepower is the engine making?

[WinMan]

Did you ever get this resolved? I had the same exact issue (non ricks tank). It was indeed voltage. You can not measure the voltage at the battery. If you do not have sufficient wire size to the fuel pump, the current through the small wire will cause a voltage drop at the pump itself. I had only 12.2v at the pump using a calibrated multimeter for industrial use. My battery was reading 13.5v. This seriously starved the walbro 255. Just FYI.

[carbuff]

Yes, I did. I installed the vaporworx fuel pump controller. I didn't have a way to actually measure the voltage at the pump during periods of high need, so I cannot be certain whether or not the voltage was stable. All I had to go on was the gauge on the fuel rail (as recorded by the HP EFI) and the in-dash pressure gauge.

What I see now is a constant pressure at the rail. It sits around 58psi at idle and cruise, but (going from memory) I seem to recall that when I got WOT, it may drop to 56 or 57psi. But it stays there consistently across the RPM range.

The engine was dynoed at 615HP before going in the car, but I have not had the chance to get the car on a chassis dyno to measure and tune it yet. I hope to do that soon.

The controller was a nice kit, and I had a close/convenient spot to mount and hide it, so it worked out well for me!

[CarlC]

1.3v voltage drop is huge. From a pump performance standpoint, going from 12v to 13.5v on an LS3 fuel module is worth a 24% performance increase.

[WinMan]

Yup. 100% agree. When I saw those numbers, I immediately knew what was wrong. I ran an 8 gauge wire to the rear of the car and put a relay mounted ontop of the DSE suspension cross beam. Pump has zero excuse now. I realize it is way overkill. Oh well.

[CarlC]

Del City has a handy wire gauge size chart in their catalog. I tore the page out and hung it on one of the cabinet doors in the garage.