Low rail pressure 17500psi max
 

I did a rail pressure reading trying to figure out why my truck is pretty slow for what it is. I have good tunes, The truck has thrown one p1093 and it did it when was trying to figure out a baro sensor issue.

I was trying to log the actual vs commanded rail pressure but it kept saying invalid pid.

The point, I did four logs, all are at 4 - 5 psi at idle, max psi at 3200 rpm at 17500 psi. I watched the logs go through and it never appears to drop off it just gets to 17,500 ish and stays.

The truck other then being slow ish does not have any other symptoms, it idles smooth, no smoke, surged only when my map sensor was having crack for breakfast, starts easy.

Fuel Filter?

you may have a weak CP3

what PW are you running when it can't hold above 17,500?

a lift pump may help a weak CP3 or large PW

PSI looks ok at idle as long as you mean 4-5,000 PSI

Both fuel filters are new as of Saturday I logged on Sunday, I don't know what you mean by PW sorry. At idle is 4-5000 PSI yes.

sorry, PW = Pulse Width. the length of time the injectors stay open per each injection cycle. i saw that you had EFI Live in your signature. a tune that runs a large PW can drain the fuel rails under WOT and cause poor performance with a weak CP3 pump and even some strong ones.

did this truck run fine and then suddenly not? any changes made to shortly before it started running like this?

This is how the truck has ran since the twins went on (i was part of the install before I purchased the truck). I think this set of twins has been on the truck for about a year now.

I got the truck and started talking to other people and asking questions about what this set up should be like, then watching you tube of trucks with same basic set up or hp ratings (where mine should be) and noticing I was pretty slow.

Larry Jewell started helping me with my tunes to make sure I had a good one and told him what was going on as far as performance and he agreed i should be pulling harder then I am.

I think my PW are at 3200 ish. I cant confirm that without looking at them but i think that is about right.

i think 3200 is on the high side but probably where it needs to be to be able to make about 500+ HP on stock injectors. even a good CP3 will normally have a hard time maintaining 20K+ PSI unless it was opened up to improve flow. this is in the realm where a good lift pump should be invested in.

what could have happened is that the truck ran fine when the CP3 was relatively new but is now getting weak and cant maintain the pressure needed.

do some googling "CP3 mod" and "lift pumps" to learn how important it for the upper HP levels

thanks Jason

Thanks for your help I appreciate it. Is there a test I can do before I start throwing 600 for a lift pump or 1200 for a 40% cp3?

it depends, are you familiar at all with EFI Live tuning, i assume your still new to it. you can try dropping the PW down to 2800 or even lower until the CP3 can keep up. this can give you a rough estimate on the condition of the CP3. it may even run stronger with lower PW and higher rail pressure.

i found my new raptor 160 lift pump on ebay for about $150. results may vary

if you are mechanically inclined you could do the mods yourself for little to nothing, but this may not be worth it if the pump is worn.

try reducing the PW down some and test it first to see if it feels like it runs stronger

Add lift pump already to my sig.

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I will give the pw a shot, I am new to tuning yes but I have been getting some pretty good guidance and I am making progress. It is going to be a bit before I can use the butt dyno to see whats going on, weather has turned back to winter and the roads are in no condition for hammer down driving.

The closet real dyno is a 4 hour ferry trip and a 700 mile road trip after so all dyno runs are done with the highly accurate butt dyno.

I do all of my wrenching, If it turns out to be a cp3 I will be the one doing the install. Not by career I am a computer geek, I just hate paying people to do stuff I should be able to do my self.

wow that was fast! at that speed you should be able to install a couple hundred lift pumps a day:jump:

so if you already had one, then just do the PW test. let us know how it goes

i feel the same way

modded my own CP3, wow what a difference. there are great write ups floating around these and some other forums on how to do it. consider doing it to the one you may put in so you only have to do it once.

once again same here. dont know of any dynos near me so it is my butt for now. seem to have worked so far. have not lost to a stop light race so far. haven't challenged many other diesels though, mostly ricers and other gasser junk

I wish I had access to parts like that but I found out the original owner put the lift and diy fuel filter in. I was looking at the race valve in case my issue was my fprv and its 40and its 40 bucks in shipping to get a damn bolt here. If I knew more about it I would go to the hardware store.

Lowered pw to 28 no differance in butt gauge, no differance in max rail pressure 17500 @ 3200. At this point I am thinking either something in the program is limiting me to 17500 or my cp3 is not capable of producing any more than 17...., or my fprv is letting anything above that go back to the tank, it is shimmed but that doesnt mean its not broke.

try using the scan tool DVT (F12) tools to command max PSI during idle to see if you get the same or different results.

I found out last night I was using the wrong pid to record the fuel rail pressure and my readings may not be accurate (Thanks Josh H) Then I found out I didnt have the correct gm pids listed so I ended up doing a re-install of efi, got the gm pids (all though most of them had a X through them) I went to bed after that.

So in a nut shell I am going to try again tonight weather permitting.

2004lb7 I will try your suggestion tonight as well.

press "shift" & F2 to validate the PIDs. this should remove allot of the X's

Thank you, I came home for lunch and validated them in the truck and got an actual vs desired log. my actual is 17000 psi, my desired is 27000, battery on laptop died before I could do the test you suggested I will have to wait till after work for that one.

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I ran that dvt and nothing appeared to happen until i put a check in the box rail pressure relay i beleive it was and the truck shut off like i turned the key off. other than that nothing that i can tell

get off work yet?

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get off work yet? :chained::work::trapped:

I tried that dvt test and nothing happened. I did click on test relay and truck died like I had turned the key off.

I did bypass my lift pump and that also made no change in pressure. I am going to do a bottle test tomorrow.

I also think I may still have issues with my MAF at idle I am seeing .8 ft\lbs to 1.2 ft\pounds. I have modified the fueling tables to max just to see what is going on and its like I did nothing all the post i have seen say you will see lots of smoke (i dont want to see smoke just an example) and i have no smoke what so ever. So I dont think my changes to my maf setting or fuel limiting tables are doing jack.

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I figured out how to change maf rates, tested in drive way at idle now seeing 5-6 ft/lbs. I did cant leave for a test ride at moment but maybe it will help out.

be very carefull maxing out fueling tables. engine can rev like it's at WOT the moment you start the truck

if you are just maxing out the bottom right corner of the table then you will most likely never hit that point.

the bottle test could tell you allot, if the injectors are returning excessive fuel then the CP3 cant build pressure. this is what happened on my rig.

are you sure this is the reading? MAF should be grams/sec or lbs/min. mine at idle is around 2.8 grams/sec or about 0.38 lbs/min

I should have been a bit more clear by max I ment I copied my normal fuel rate and placed it in the table essentially replacing the 120 max to 170 same as the normal table when running correctly in theory.

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I used the sae.maf pid imperial and it listed it in ft\lbs.

ok, that make sense. have you tried your stock tune and seeing what the rail pressure does?

when you commanded max psi during idle did you log the {actual fuel rail regulator current}? did it match the [B1010 rail pressure valve current] in the tune? 0 or low amps

if the valve current zeroed out per the tune and your PSI is still low then i would believe that ether the CP3 is bad or the injectors are returning too much fuel. the bottle test should tell you if it is the injectors. being that it is an LB7 i would think that it is the injectors.

mine went out last November and i had similar symptoms. it drove around town fine with out smoking much but i didn't have much top end power and couldn't build rail pressure at idle. this eventually got so bad that it started dieing at intersections. then i couldn't even get it to start. thats when i replaced the injectors. runs like a champ now, same CP3.

while i was at it i pulled the CP3 and did the high flow mods to it. had to increase the valve current to pull the idle PSI down when done

I went into the dvt and said go. then nothing then I started putting check marks in boxes and it died on the relay one. I stopped after that when i realized i really didnt know what I was doing. I am going to hold off until I do more research about how to do one and what I am actually looking for.

I dont know that it makes any differance but its a LLY.

I have not returned it to the stock tune yet. I am defianlty feeling like this :argh: though.

try this out. see attachment

thats great, LLYs are easier to figure out what injector has a problem and to change them is 10x faster. LLYs dont have as many injector problems as the LB7 but it still happens. the best injectors are in the latest trucks. if i could only fit a set of those piezo injectors in mine

before you get too far into "fixing" anything do the ice pick trick on the injector harness. this is a problem the LLYs have.

We did the bottle test, it passed. We unpluged fpr and only got 17500. I think a fpr is in my future.

may just be stuck. do a google search for the regulator mod. it will show how to open the regulator. you could also try pushing on the plunger with a thin rod,needle it see it it is before taking it apart.

if the regulator is burned out then the PSI should go to max. right now it is somewhere in between max and min.

the plunger is pulled by a solenoid and pushed by a spring. if the solenoid stops working then the spring pushes it all of the way open

Wow I read your post last night late and tore into it first thing this morning, and got evertying out of the way and then the reality of the 3 torx bit set in I think I managed to get on one of them then I decided that the cluster f that was about to happen trying to get them out let alone in is going to happen only once with a known good one going back in. They obvously thought that part would never go bad.

those 3 torx screws are a pain. took me like 2 1/2 hours just to get out those three screws. later i ended up taking out the CP3 and it was not much more work. sure made putting the regulator back on much easier.

i have heard of people cutting down torx screwdrivers with the hex shank just to get them out.

I like the idea of just pulling the cp3, I think I will just do that next time and just not fight it.

so did you find out if anything is wrong with it?

LOL No, I got to the point of modifying tools to get to the bolts and decided that was it until i had a gaurenteed working replacment, but found out the pipe that was in the way the one that goes in to the block that sends pressurized air to both sides of the block comes out by giggling for lack of a better term.

like an upside down "Y"? got mine out pretty easy after taking a lot of junk off.

hardest bolt is the one on the back left bottom by the turbo. make sure you stuff rags in the holes as it's a short drop down to the intake valves from there. you would hate to have to pull the heads off to get a dropped bolt

i thought i did and had to buy a boro scope camera to verify nothing was down there:scare2:. found the bolt under the turbo with the camera instead. :jump:

Yes that would suck thanks for the heads up I will make sure all holes are plugged with something easy to remove.

I imagine you were sweating bullets for a bit, I know I would be.

for three days!!! even had help come over to look for it. couldn't sleep at night, kept running the scenario threw my head - where is that f#@$in bolt? should i just start the truck? :baby:

well with the boro scope i found it under the turbo. man it felt good. the engine went together so fast after that.

Glad it worked out for you, I do not envy that situation. I know I would have lost sleep to. :dang:

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Lets put it this way, I am loosing sleep over mine and it starts and runs good LOL. I have a grudge match coming up, Stock 2010 Hemi 1500 (should not be a problem but it is) vs 1997 F350 cc power stroke with intake, exhaust, dp tuner, ic, stage two sticks, super duty hpop, and a built trans ball park 450hp ish, it is quick, vs my truck. We are planning on a trip to the local drag strip in April / May (which is a 4 hour ferry ride plus a 700 mile drive after that) I have no intention of being 3 rd.

let us know when you get it out so we can help you get your truck running in top shape. would like to see you give em a wippen :bat:

Will do, it will probably be this weekend. My truck it to tall to go in the garage all the way and it makes for a cold time doing it at night. Even though its not much warmer during the day it is warmer non the less.

Will a LBZ regulator work in a lly?

it will fit but if it idles funny then you will have to rescale the current tables

Decided to wait until I had a spare fpr in my hand before messing with the old one since truck still runs to get me to work. But I have the patience of a two year old. Ugg part is should be here tomorrow.

Who ever decided to put the fpr there is a evil little person. Once I gave up and round down my 1/4 drive torx it went a little easier. But I do not think it resolved my problem. I didnt data log but butt dyno says its the same.