Factory fuel pump
That's why we sell the correct one for the early hemis and a different one for later model ones.....FYI 06 FSM says 58 +/- 2 psi not +/- 5 psi. Anyway, I was thinking we were talking early Hemi and I have to look pressure up in FSM for the specific year the cust has as they changed at least once...which is why we carry two different filter/reg units.
Funny thing, LOTS of jeep customers running Hemi with stock TJ pump and never a problem, I must not know mopar very well, only been screwing with them and building harnesses for last 18 years, only have about 30 years as a FI tech. Sorry for being so ignorant.
The only Hemis
earlier than the 2004 is the debut platform 2003 Ram 1500,,,,and I'm pretty certain the 2003s run 58psi as well. So ALL Hemis should be running a regulator delivering 58psi +/-5psi and NOT 48psi, sorry that's just incorrect. All OTHER gas engines that used the JTEC PCM(magnum, 4.7, 3.7) ran lower fuel pressure,,but NOT Hemis(NGC PCM).
The factory NGC PCM's fuel trims can account for a misinformed owner running the wrong(lower) fuel pressure at idle, cruise, ie closed loop so the error
might go unnoticed. Once headers up the VE and transport delay to the O2 sensors, drivability should improve with the
CORRECT fuel pressure the PCM was calibrated for.
Unwittingly running a lower fuel pressure becomes the biggest issue at WOT obviously, since its open loop and there's no active feedback. Luckily the saving grace for an underperforming fuel system is that most stock tunes run fairly rich at WOT,,,,but again it's certainly
NOT advised.
Now with that said if the engine has an
aftermarket EFI(holley, fast, ect) and it's been tuned to account for a lower fuel pressure, then it's all good.