LB7: low rail pressure when hot

[deway2go]

Hi all,
2002 cc/sb actual fuel rail pressure is good when it is cool but as it warms up it is more inconsistent. I have rebuilt the filter head and replaced the filter less than 200 mile ago. when I first start up the desired and actual FRP is pretty close +/- .2Kpsi but wont go over 10Kpsi when commanded . once the truck is warm the desired and actual are out of range and the Actual FRP wont go over about 8.5Kpsi . throwing 1093 and 1094 codes. I have cleaned the MAF, checked the air filter( still clean). Is this a weak CP3 or FPRV, or could it be a crack in the filter head. i received my CTS2 about a month ago and that is when i noticed the issue. before that when i ran the Bullydog on Performance tune it would fall on its face once in a while if i held WOT for more than about 10 secs. i have taken the BD out and am running the stock ECM until i get this figured out. thanks in advance for all your guidance

 

[skintback]

Any fuel in the oil?

I would start with a brand new filter housing from the dealer there about 125 bucks and come with a filter. The first thing that comes to my mind is a very weak cp3 pump bad regulator or the pickup in the fuel tank is clogged or a restriction somewhere down the line. the injectors could be returning to much fuel as well

 

[Bustedknuckles]

Probably bad injectors returning too much fuel when they get hot.

 

[Brent@LDS]

Hi all,
2002 cc/sb actual fuel rail pressure is good when it is cool but as it warms up it is more inconsistent. I have rebuilt the filter head and replaced the filter less than 200 mile ago. when I first start up the desired and actual FRP is pretty close +/- .2Kpsi but wont go over 10Kpsi when commanded . once the truck is warm the desired and actual are out of range and the Actual FRP wont go over about 8.5Kpsi . throwing 1093 and 1094 codes. I have cleaned the MAF, checked the air filter( still clean). Is this a weak CP3 or FPRV, or could it be a crack in the filter head. i received my CTS2 about a month ago and that is when i noticed the issue. before that when i ran the Bullydog on Performance tune it would fall on its face once in a while if i held WOT for more than about 10 secs. i have taken the BD out and am running the stock ECM until i get this figured out. thanks in advance for all your guidance

How many miles are on your injectors and CP3?

 

[THEFERMANATOR]

Most likely injectors or CP3, only way to know is a return rate test. And LB7 filter heads are over $500 list, but many get longer hoses and say they can make the LLY+ filter head work.

 

[deway2go]

Brent, looks like the stock CP3, the injectors were done at 265k according to PO by dealership.

thefermanator, DMAX store has one with out heater unit for $110. hope to be able to do the inj return and the fprv bottle test this weekend.

PS: it did get better after the filter head rebuild. i think i have multiple problems here

been doing a lot of research on here. great site love the support given. :thumb:
OBTW called about a filter head from stealership- $677

 

[THEFERMANATOR]

The without a heater is an lml. Its the same as the 04.5-10 filter head, just no fuel heater. It still requires new longer hoses to make it fit.

 

[Brent@LDS]

I'm thinking the same, injectors or CP3. Time for a return rate test.

 

[Brian Hynes]

I have a little different problem. 2003 LB7, all injectors done at 175.000 Kms, it now has 241.000, getting smoke at idle and surge at idle. Took it to GM, they put it on the scanner, injector readings as follows;
Injector 1. 0.50 ms
Injector 2. 0.12 ms
# 3. 0.34 ms
#4. 0.29 ms
# 5. 0.34 ms
# 6. 0.32 ms
#7. 0.32 ms
#8. 0.34 ms
Rate Cyl. 1 5.0 mm3
When the engine make that surge, you can hear it and see a little drop on the RPM tach, then Injector # 2 drops of to 0. GM said the number 2 injector is bad. This was the only test they did, would you want a second opinion before you did the injectors again or does these reading clearly indicate that # 2 injector is in fact bad. He said that surge would be caused by the injector, my understanding from on here the surge would be caused by the FPR. HELP....

 

[THEFERMANATOR]

I have a little different problem. 2003 LB7, all injectors done at 175.000 Kms, it now has 241.000, getting smoke at idle and surge at idle. Took it to GM, they put it on the scanner, injector readings as follows;
Injector 1. 0.50 ms
Injector 2. 0.12 ms
# 3. 0.34 ms
#4. 0.29 ms
# 5. 0.34 ms
# 6. 0.32 ms
#7. 0.32 ms
#8. 0.34 ms
Rate Cyl. 1 5.0 mm3
When the engine make that surge, you can hear it and see a little drop on the RPM tach, then Injector # 2 drops of to 0. GM said the number 2 injector is bad. This was the only test they did, would you want a second opinion before you did the injectors again or does these reading clearly indicate that # 2 injector is in fact bad. He said that surge would be caused by the injector, my understanding from on here the surge would be caused by the FPR. HELP....

Those numbers are worthless, they aren't even balance rates. Without knowing the rail pressure, you can't even convert them into a useable number.

 

[deway2go]

OK might as well start collecting prices for CP3 and injectors.
Brent can you get me prices so i can start preparing my Bank Account for the trauma (Read Wife). I would really like to go with the SAC nozzles. but finances may dictate otherwise. I may do the CP3 first and see if it helps. hoping i don't need injectors just yet.

I am actually just down the street from dieselogic . but have heard very few good reviews from their injectors. So not even going to bother with them . need quality stuff that will last.

 

[Brent@LDS]

PM sent!

 

[Davidz28man]

Bye any chance when it's hot do you smell even a hint of diesel?
I only ask because mine was throwing them codes. When I changed my fprv I noticed
The soft lines going into the cp3 were cracked and fuel soaked changed them and problem went away. But it could have been the fprv too. Lines needed changed any way lol

 

[deway2go]

I plan on changing the filter head and all soft lines on top of the engine at the same time. this way i know they are all good. i can hold rail pressure up to about 9-9.5k consistently, and when i let off after it demands 15+ it will spike to 13.5-14k. running at 65 demand is about 12.5 and actual is running 9-9.5. I have never seen it go above 15 in the short time i have had my CTS2