Rail Pressure Oddity

[Black AOD]

So my truck has been seeing a small and odd fluctuation here and there in rail pressure recently. I noticed it about 2-3 weeks ago, after idling for about 10 minutes and then leaving to go to work, I'd get out on the road and get into the throttle and it would go and then for a few seconds it didn't really want to fuel and rail dropped to 2.2k psi for about a tenth of a second and then the pressure spiked and it was fine and then a second or two later it did it again. Then the rest of the day it was fine.

Exact same thing next morning except it only dropped to a low of 4.4k PSI then it was fine all day. It had a really small drop during throttle going over a bump later that day but cleared right up. Nothing else after that.

My truck uses an Aeromotive lift pump so I changed the CAT filter about a week ago since it had about 8k miles on it and they do fuel filtration/water separation all in one and since then no issues at all until today.

I hit a bump this morning kind of hard on my way into work and when i was coming out of a stop sign it didn't want to fuel as hard down low and rail wouldn't maintain, then again a few seconds later, then it returned to normal. Then I was driving home from work and going up a slight incline on the highway it started to not want to fuel as hard and rail dropped from about 10.5k psi to 9.0k PSI and then it spiked back up. Did it again a few seconds later and the the rest of the drive home it was fine. I'm at a loss.

I spoke to Morgan @ Midwest a bit ago and he agreed it's weird. I have zero fuel leaks. The truck on the big tune which makes 850+ holds 24.5-25k PSI in WOT pulls and even did a few 4wd boosted launches to test it. RP holds steady at 24.5+ consistently. It makes 6k rail pressure @ Idle, doesnt smoke out the tail pipe any more than normal, RP graph on the H&S doesnt show anything out of the ordinary.

My personal thoughts/consensus is a rail pressure sensor is going bad, a regulator is sticking, a PCV on one of the k16's is malfunctioning, or one of the k16's is going bye bye.

Any thoughts or input would be appreciated.

For those who don't know my setup, basic list is below.

Motor is almost fully built minus it doesnt have billet rods.
Midwest Diesel 5R Billet Comp Trans
Midwest Diesel Dual Fueler K16 Kit
Elite Diesel 2.0 High Power Compounds
Elite Diesel Stage 3 Low Pressure Fuel System
RCD 60% Injectors
Both K16's are used OEM pumps. NOT REMANS. They have fairly low miles on them.

 

[djr4x4]

Tuning?

Sent from my SM-G935T using Tapatalk

 

[Black AOD]

Tuning?

Sent from my SM-G935T using Tapatalk

Idk how I forgot to post that. MCC tuning by Ghead on a Mini Maxx

Sent from my VS990 using Tapatalk

 

[78f100]

I had one at the shop a few weeks ago that would idle great cold, after 30+minutes it would get a lope. Rp was surging from 5.2 to 2.2, checked low pressure all was fine. Did the hpfp test on ids, passed just fine. I decided to try the rp sensor first and no more issues, I would give that a shot if all else tests good.

 

[6.0 Tech]

Sounds like frp sensor. Change the uvc harness while youre at it, ive seen the sensors leak internally and soak the connector, plus its cheap insurance while youre under the valve cover.

 

[Black AOD]

I had one at the shop a few weeks ago that would idle great cold, after 30+minutes it would get a lope. Rp was surging from 5.2 to 2.2, checked low pressure all was fine. Did the hpfp test on ids, passed just fine. I decided to try the rp sensor first and no more issues, I would give that a shot if all else tests good.

Mine doesn't surge anything like that and it certainly doesn't lope at all like the one you messed with but based off that and my thoughts already I honestly do think its an FRP sensor. Ill find out.

Sounds like frp sensor. Change the uvc harness while youre at it, ive seen the sensors leak internally and soak the connector, plus its cheap insurance while youre under the valve cover.

Was replaced not long ago....Ill check though.

 

[djr4x4]

When the frp drop while driving. What speed r u at? My s.p.a.r.t.a.n tuner got glitchy on me after coming back from the shop and when accelerating my frp would climb and approx 20 mph my frp would start to drop to around 2-3 k and out of the blue jump back up and run fine. Wiped all of my tunes and Reinstalled fresh and all was fine after that.

Sent from my SM-G935T using Tapatalk

 

[Black AOD]

When the frp drop while driving. What speed r u at? My s.p.a.r.t.a.n tuner got glitchy on me after coming back from the shop and when accelerating my frp would climb and approx 20 mph my frp would start to drop to around 2-3 k and out of the blue jump back up and run fine. Wiped all of my tunes and Reinstalled fresh and all was fine after that.

Sent from my SM-G935T using Tapatalk

Speed is different. It did it at 65 mph on the highway then another time when only going 15 mph getting into the throttle. It varies. I may try the re uploading tunes though. I dont think it will help but it's worth a try.

 

[djr4x4]

I tried it as a last ditch effort before going back to the shop.

Sent from my SM-G935T using Tapatalk

 

[78f100]

Mine doesn't surge anything like that and it certainly doesn't lope at all like the one you messed with but based off that and my thoughts already I honestly do think its an FRP sensor. Ill find out.



Was replaced not long ago....Ill check though.

My customer brought the truck back last week for brakes and I asked how it was doing, he said it was fine but felt weaker than before. He has a old mini maxx and it was freakishly strong and smokey with the old sensor, I tested it again and rp was exactly what was desired. I think the old sensor was reading wrong all the time causing the pump to work really hard, who knows what rp actually was. My point was the sensor can cause all sorts of issues, maybe that's all that's wrong with yours and it's the cheapest and easy to replace. Hope you get it figured out.

 

[Black AOD]

My customer brought the truck back last week for brakes and I asked how it was doing, he said it was fine but felt weaker than before. He has a old mini maxx and it was freakishly strong and smokey with the old sensor, I tested it again and rp was exactly what was desired. I think the old sensor was reading wrong all the time causing the pump to work really hard, who knows what rp actually was. My point was the sensor can cause all sorts of issues, maybe that's all that's wrong with yours and it's the cheapest and easy to replace. Hope you get it figured out.

Me too, thanks man!