Low side fuel pressure

[18silv5.3]

Hey guys, I’m having an issue with my 2018 5.3 where sometimes it will randomly hiccup and for a second lose all power(like half a second). I did a data log with hptuners and noticed around that same power drop my low side fuel pressure dropped to 23psi. Will these trucks drop that low with the new fpcm controlled fuel system? My old trucks stayed 48psi ish and up at all times. Or do I have a failing low side pump? I’ve noticed that sometimes as it builds pressure before starting it sounds like it’s grinding gravel in the tank. But drives perfect otherwise. 

[anthonymason59223051]

on 5/02/25 i got the p2635 code and i am having some of the same symptoms as you are describing and have been for a while (maybe 3 or 4 months)... under moderate accel from a stop it will hiccup or cough, the only way i can describe it is it sounds like the truck is making the sound "puh". then it immediately acts like traction control engages and it falls on its face. looking at commanded versus actual high side pressures with no load in park is see a commanded of 881.8psi and actual of around 750-770psi. low side pressures, my scanner does not show commanded low-side but i can see actual pressures bouncing from 40-60 give or take a couple psi, verified with a mechanical gauge. while driving, the high-side stays CLOSE to commanded but always under by 50-100psi. but low-side? the graphing feature has the low-side looking like a seismograph during an earthquake, 24-64 min-max. i do NOT have the gravel sound you are describing though. it only threw the p2635 one time on 5/02 and has not come back after clearing, but the fuel pressures remain all over the place. my truck is a 2018 Silverado CCSB 4x4 LT TexasEdition with 109k. i figure it is probably about time for a low-pressure pump anyways... they are cheap enough through RockAuto. i will let you know how it acts after. when i pull the heads for a cam/lifter swap, i plan on doing the HPFP since i will be right there. going to throw an L86 intake and throttle body while there as well since it will need tuned anyways HAHA!

[anthonymason59223051]

finally got the time to do the low-side fuel pump yesterday... was starting to get to the point i was having extended crank times on start-up, a felt miss-fire at idle (not a dead hole miss but noticeable) and mild surging at cruising speeds when you increased load (like press/hold the accel button on cruise.) went for a drive before with the scanner to see where i was at on pressures and it was showing even lower erratic readings than before. before it was 24-64 min-max, now it was down to low teens to 51psi and had to feather the throttle for any kind of moderate acceleration. after replacing the pump, it is now reading upper 30s to low 70s and acceleration back to normal, no more coughing or stumbling, smoother idle, faster start up than it has ever been since i have owned the truck starting in February of 2021. it may not be your problem, but it is certainly something to look into!