High Rail Pressure While Cruising

Six_Sloww · Sep 20, 2016

Been battling issues with hot fuel, way hotter than what people with similar modifications are seeing also noticed my injectors are really loud lately... Took me a while to notice but my Rail pressure is way too high. Going 40mph down the street just maintaining speed I'm around 25k. Highway at 80 I'm damn near maxed out around 30k (max for me is 31.5)

What happens is while I'm accelerating everything is normal, somewhere in the 15k range. When I get up to speed after about 15-30 seconds of maintained pedal position my Rail pressure will jump up 5-7k. If I let out it drops back down for 15-30 seconds then jumps back up

The tuning didn't change, but I did try to swap over to an h&s canned tune to see if it went away and it didn't.

Any ideas?

Six_Sloww · Sep 20, 2016

https://vimeo.com/183576455

Sent from my SAMSUNG-SM-G935A using Tapatalk

MrMike2010 · Sep 20, 2016

Complete shot in the dark here but maybe you have a bad fuel temp sensor? Possibly it ramps up pressure to heat the fuel up.

Six_Sloww · Sep 20, 2016

MrMike2010 said:
Complete shot in the dark here but maybe you have a bad fuel temp sensor? Possibly it ramps up pressure to heat the fuel up.

I think the fuel pump is in charge of getting the fuel up to temp, it has a valve inside of it that will recirculate fuel through the high pressure system until the fuel is up to temp then it lets it flow back to the tank. The fuel temp sensor is used for fuel calculations, but I could be wrong.

CATDiezel · Sep 20, 2016

I asked that question awhile back. With Spartacus tuning I saw very high rail pressure in the 600hp tune. At cruising as well.

Six_Sloww · Sep 20, 2016

Just found a p228f - related to the pressure control valve

powerstroked08 · Sep 20, 2016

CATDiezel said:
I asked that question awhile back. With Spartacus tuning I saw very high rail pressure in the 600hp tune. At cruising as well.

Was it commanded rail pressure? Or just creeping like sixslow?

Six_Sloww · Sep 20, 2016

No creep, just jumps up and will hold until I let off the pedal and get back in it. Then the pressures are normal for a short time until they jump back up.

CATDiezel · Sep 20, 2016

powerstroked08 said:
Was it commanded rail pressure? Or just creeping like sixslow?

Well I cannot say for sure but it's obviously commanded being it drops back down if I run the 400hp tune.

I thought it was oDD seeing 25k rail at Super light throttle taking off. I was NOT used to that with my 11 and HS tuning.

powerstroked08 · Sep 21, 2016

Weird. I guess its weird because there are 2 separate trucks having similar issues. While one is running H&S and the other is running Spartacus.

sideactiondiesel · Sep 21, 2016

Weird. I guess its weird because there are 2 separate trucks having similar issues. While one is running H&S and the other is running Spartacus.

Or maybe someone knows but no saying LOL

Six_Sloww · Sep 22, 2016

Good news! No rust!

Only clean metal

Vader's Fury · Sep 22, 2016

That's not good. Hpfp eat itself?

Six_Sloww · Sep 22, 2016

Dunno for sure. Going to start with cutting filters open and go from there.

I put a sump in it and had half the tank in buckets and the fuel was clean. So there's not much if any making it down the return side.

I mean the truck runs fine, holds 31.5k no problem and made 976 hp two weeks ago lol.

maxxedout · Sep 23, 2016

I don't know if there's any way to find this out, but it would be interesting to know what started the failure. What would put more strain on the HPFP(s)? Hot fuel or running higher-than-ideal rail pressure while cruising? Maybe a little bit of both?

Six_Sloww · Sep 23, 2016

maxxedout said:
I don't know if there's any way to find this out, but it would be interesting to know what started the failure. What would put more strain on the HPFP(s)? Hot fuel or running higher-than-ideal rail pressure while cruising? Maybe a little bit of both?

Yeah I'd have to take the hpfp apart to see if it is actually failing.

I'm going to go through my pre pump strainer and frame mounted filter tomorrow. If I find any more metal it's all coming apart and I'll pinpoint the failure.

I don't think hot fuel has anything to do with it.

Six_Sloww · Sep 23, 2016

High Rail pressure was likely due to a sticking pcv valve, which is sticking because of the contamination.

maxxedout · Sep 24, 2016

It definitely makes sense that the metal debris on/in the PCV was causing it to stick and thus creating the higher-than-commanded rail pressure situation. I just wonder what started the sequence of events that caused your issues. The high rail pressure could be the reason why your fuel was getting so hot, right? If your HPFP was starting to go, I'm sure hot fuel wouldn't help matters. I'm very curious to find out where the metal came from. Also, it would be interesting to see if your fuel temps come way down once the fuel system is cleaned up. The sucky part is that I've never heard of anyone having luck flushing the high pressure system on a 6.7. I work for a dealer, and I know our shop only handles contamination issues one way: every single component gets replaced. That's bad enough news on a stock truck without dual fuelers, hot injectors, etc. Like I said, I'm just curious to see where this all started. Best of luck to you with getting it resolved.

Six_Sloww · Sep 24, 2016

Higher than commanded Rail pressure didn't help, but it's also my fuel pump setup that contributes to the hot fuel.

If I find anymore contamination all the high pressure lines and rails will be replaced, I'll sending the injectors out to asses the damage and replace the cp4 with a stock cp4.2. The cp3 should be fine.