Are you venting the tank as suggested in the instructions?

"All MagnaFuel high volume fuel pumps also require a -8 or ½” vent in the fuel tank. The venting on stock tanks is not adequate."

If your baseline is 58 psi at idle, then the FPR should reduce fuel pressure by about 8-10 psi if your vacuum is about 8-10 psi at idle to compensate for the vacuum at the tip of the injector (FPR reduces rail pressure to the injector down to 48 psi) .

If your baseline is 58 psi at idle, then the FPR should increase rail pressure equal to boost (14 psi) to overcome the pressure of 14 psi at the external tip of the fuel injector (58 + 14 = 72 psi - so you need 72 psi at the rail/FPR gauge when at 14 lbs of boost).

The FPR will react 1:1 throughout the entire range from idle (reduce/subtract) all the way to maximum boost (increase/add) and why the IFR table should be flatlined to whatever the baseline is.

Yep regulator seems to be working correctly and I have a -8 vent as well as the factory evap still in place. I can blow on the vent lightly and it blows out the bulkhead feeding the pump so it’s clear and flowing well. I’m really stumped.

aem wideband in the rear o2 bung on the drivers side reads good afr every where idle and drive ability are amazing. Afr in boost is 11.5 to 1 on the gas scale all the way up just maxed on duty cycle about 150 rwhp sooner than I think I should be.

If you can log the EGR pintle position then you can wire in a sensor to log fuel pressure. Are you running a boost referenced FPR? I always run 4 bar base pressure and a 1:1 rising FPR.

yes it’s the Magnafuel 2000 hp boost reference regulator. I’m at 55 psi base with 14” vacuum I idle at 48 psi. With some revs to hit boost it jumps right up to 58 psi, but I’m not setup to log fuel pressure in hptuners. I did check voltage at pump is 13.5 and log voltage at controller with hptuners is steady at 13.7 at wide open.

I agree - weird. My Racetronix 98 hotwire kit and upgraded Racetronix 255 lph pump handled 565 rwhp (Mustang dyno - 60 lb Mototron)) as was still at 75-80 percent duty cycle. Which BTW is what Racetronix states that it will support. I have since upgraded to their duel 450 lph kit which will easily support up to 850-900 rwhp (gasoline). IMO two pumps are better than one huge pump since one 255 lph will support 99 percent of my driving. When I need the additional volume and pressure from pump two it fires up.

Just can't see recyling 200 lph more per hour thru the tank when it's not needed (one 450).

You need to log the FPR. If you're base is 55 and you're adding 14 psi you should be close to 70 psi at max boost.

Agreed...I just started digging into this a couple days ago because I want too up the boost. Started with checking voltage and making sure the regulator was working at all. Magnafuel said check post pump 25 micron filter which the way I’m setup required me to empty the tank. I did that last night and filters were fine, but I’m going to put new filters in anyway to satisfy support. Filters should be here today and I’ll go from there.

Any chance the gauge on my fuel rail is way off? Seems unlikely with how easy it was to tune and how well it performs just maxing our idc way to soon.

Im on straight E85.

Now Magnafuel says I’m at the limit of the -10 and -8 line I’m running which isn’t what I was told when I talked extensively with them about planning the setup exactly the way I have it.

Im also going to try running the pump ground to a different location. I’m just going to put it back together and live at my current boost level for a while and rethink things I’m losing patience and need to step away from it.

BS.....people make 750whp on stock lines. I had a -6 and it was good for plenty. Magnafuel is jerking you around.

I've dealt with this kind of issue quite a bit and will throw in my $.02 from those experiences.

IMO, the problem is not the injectors. If they actually flowed 940cc, that's about 91lbs and using a BSFC of .76 for E70 (assuming the AFR is not fat), they should support about 700rwhp @ 85% DC.

If the injector DC is 95 0r 100%, it doesn't necessarily mean you are out of injector. If you are not getting proper fuel delivery, the fuel pressure is going to drop and the ECM will try to compensate by increasing INJ DC. As noted by others, the fuel delivery problem could be from pressure not rising with boost, incorrect micron/restriction pre-pump, low voltage at the pump, not what the ECM is reporting or the pump itself. As for the pump itself, I cringe every time I see someone quoting the Magnafuel marketing numbers. Those numbers are meaningless when it comes to forced induction and worse when using ethanol. Since Magnafuel does not publish flow charts, you need to call them and ask for the flow number at the pressure you run (base + Boost). They'll probably give to you in gal/min, so convert that to lb/hr, divide by .76 (BSFC for E70) to get FWHP. But wait, there's more. You need to convert that to RWHP and then reduce that number by approx. 10% to account for flow loss from friction in the hose, fittings, especially with bends (not all fittings are made equal), and the filter. Only then will you know what the pump will actually flow and you might be surprised. If the final number is enough to support 700rwhp, then focus on the other things mentioned, like voltage at the pump, fuel pressure, etc. You absolutely have to find a way know fuel pressure under boost for more than a quick flash and voltage at the pump.

Like I said, I've dealt with these issues and anything I say is from my experiences. I am one of those who did not have luck with the 4303, switched to dual AEM380s and haven't looked back. So, in summary, if the INJs can flow enough and the pump flow is enough (I think it should be), then you need to determine what is causing the fuel delivery problems. Don't spend anymore money until you make that determination. FYI, Wallace calculator says about 1100rwhp for me and I am using AUS 1400cc injs @ 50psi, with 2 AEM380s running E55 and 2 10gph alky nozzles. You should have enough to support what you're trying to do. You just need to do a little detective work. If the problem is the same going from a 4301 to a 4303, that's a clue.

Good luck.

Thank you for the reply. When I went from the 4301 to 4303 I also added about 3 psi of boost. So I gained from the 4303 just not as much as I should have in my opinion.

The filters looked good and passed the test Magnafuel recommended. I went ahead and put new filters in anyway. 74 micron pre and 25 post just as Magnafuel suggested. I also ran a new ground from the pump to the subframe since I was only grounded to the body previously.

Same 55 psi base and I was rich every where except idle. In boost I was mid 10’s afr so something definitely changed. I made some adjustments and have all my afr’s back in line. I just went out again and was 73 percent idc at 6000 rpm with an 11.2 afr on the gas scale. Things escalate quickly above 6000 with a procharger, but I definitely think it’s an improvement. Traffic didn’t allow my to get above 6000.

Im going to enjoy the car for a bit and run it in the local 1/8th before the end of the month. I’m also going to get setup to start logging fuel pressure to see what is going on and make for easier trouble shooting in the future.

I still dont think my fuel system is performing up to my expectations, but definitely an improvement.