Actual rail pressure not keeping up to desired. 02 LB7

[john_we1der]

Hello everyone. I am hoping that someone can help to point me in the right direction on this issue I am having with my 02 LB7 with 350k on the clock. I am having trouble with the actual rail pressure not keeping up to desired under heavy pedal application, particularly when stabbing the accelerator while already running down the road; i.e accelerating at speed increases passing through towns. The truck is mostly in stock configuration, with an addition of a Fass 100gph lift pump, S&S SAC00 injectors replaced about 60k ago, fuel pressure relief valve replaced over this last weekend. It is a federal emissions with no EGR and stock 3.5" exhaust straight pipe.
I am new to EFI Live tuning and have done quite a bit of research before jumping into attempting to build my own tune for this truck. I am wondering if I am asking too much out of a stock configuration LB7 or if I have something off on the timing or fuel calls. Can someone please take a look at my tune file and log and see if you can help me to get this figured out? I would prefer if someone could give me some information on what I am overlooking and/or have dead wrong and give me some guidance on how to get to where I want to be. Overall, I would like to end up with a tune that provides a decent fuel economy (current MPG of 16 +/- 1) with a decent amount of pep in the step. I have set the timing table for my tune based off of the timing calculators v3 and v3.1 found posted on this forum (thank you to all who have made those valuable resources available for FNG's like myself).
Thank you in advance for your time and trouble in attempting to help me get this figured out!

 

[TheBac]

Original CP3? At that mileage, it could be tired.

 

[john_we1der]

That's what I'm hoping is not the problem. It seems to do alright holding rail pressure when the motor is below operating temp and when I'm not on the pedal too much, but the thought that the pump may be at the end of its life has crossed my mind. I'm just really not looking forward to the cost of replacing the pump and the amount of time to get it done.

 

[Bdsankey]

Does it have the same issue on a stock file?

 

[john_we1der]

I was going to switch back to the stock file to compare. I will do that this evening and run a log on it tomorrow on my way to work.

 

[JoshH]

From what I'm seeing in the log, it looks like either a supply issue or a bad injection pump. Have you verified the FASS is working properly and supplying good pressure under load? If that checks out, I would start looking at the CP3. You should be able to use the DVT function of the scan tool to control rail pressure at idle. See how much pressure it will build.

 

[john_we1der]

I haven't checked the pressure coming off of the fass. I did replace the filters last week and the pump sounds healthy, though I need to get a pressure gauge hooked up and verify. What would be a good pressure to see coming from the fass? I thought I had read somewhere before that the ficm on the lb7 does not like to see really any pressure coming into it since it's stock setup is to see vacuum, but I could very well be wrong. I guess I'm really just grasping at straws and hoping and praying it's not the cp3 itself lol

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[Bdsankey]

I haven't checked the pressure coming off of the fass. I did replace the filters last week and the pump sounds healthy, though I need to get a pressure gauge hooked up and verify. What would be a good pressure to see coming from the fass? I thought I had read somewhere before that the ficm on the lb7 does not like to see really any pressure coming into it since it's stock setup is to see vacuum, but I could very well be wrong. I guess I'm really just grasping at straws and hoping and praying it's not the cp3 itself lol

Sent from my motorola edge 5G UW (2021) using Tapatalk

At your mileage I wouldn't be surprised if it was a CP3.

The FICM has no problem with the 8-10psi that an aftermarket lift pump is typically set at. I do agree with Josh, based on the log you either have a supply problem (IE fuel volume/pressure to the CP3) or a weak CP3. It could be something else but all the signs point to those two main issues.

 

[2004LB7]

The FICM can probably take 100 psi, possibly more before it has issues.

Have you ran a return rate test yet to see if anything is returning more fuel then it should? If it's too much that can put a strain on the CP3's ability to keep up. If the returns are good then it's either a restriction in the supply or a weak CP3 (assuming stock tune)