Ross R

2007.5 Silverado LTZ Crew Cab 5.3 NNBS (GMT900) Lean both banks, no external air leaks found and averaging 25% fuel trim on each bank.



I’m Ross and I’m a parts changer. (Hi Ross!!!) I’m ashamed for not figuring this out but I’m stuck really needing some help. This started about 6 months after a black bear tune and AFM delete. I love the tune and realize this not the problem, but nonetheless spent several weeks trying to teach myself how to diagnose fuel trims, tried several things like cleaning MAF and throttle body, spraying starter fluid around joints to look for leaks, etc. . Next I found a local reputable shop and let them spend two weeks smoking the intake system multiple times while trying to figure it out, (and me renting a truck) they changed a couple of exhaust o2 sensors, and gave it back to me, not fixed. I spent more at another spot that couldn’t figure it out either. I try to not be an idiot, these were both shops with great diagnostic reviews, I have not gone to the dealer for this but only because I can’t afford for them to lie to me too.

This leads me to deciding, well I love the truck, it’s paid off, it runs like a top, clean, no visible smoke, no leaks, I’ll start methodically going through each system if I have to and replace things that I have learned are usually the problem in order. I can do it myself, I’m a contractor and a struggling family man with no dough, so my daily driver needs to be ready if I need anything. Next, the part replacement started and now that I have replaced (and correctly torqued in pattern when necessary) everything, the numbers are slightly better, but still ridiculous, setting lean codes and I’m sure it’s tripping the brake/traction control system as well.

No other problems, no misfires known of, etc. . Now I bought the truck with 100k, started a mobile1 synthetic oil regimen, have changed all serviceable fluids, blah blah blah. I’m going to attach a list of most things that I have done/changed. Everything I have bought has been stock, mainly ACdelco. Some of these things were not for lean issue but I try to keep a list so I can remember what and when I changed something. I’ve decided the problem must be internal but I have the AFM deleted so it shouldn’t be lifters right?

Well here’s the list, please help.



Silverado parts replaced



97,xxx

A. Bought truck, started 5k oil changes with Mobil1 full synthetic

150,xxx

A. Front wheel hubs, suspension joints and brake switch attached to

pedal arm.

B. Fluids (tranny 4 qt pumped from top, coolant, rear end, brake fluid,

and power steering.

C. Reengineered Dorman valve cover due to excessive oil

consumption

D. Kenwood touchscreen head unit with Nav, HD radio, Apple CarPlay,

Android, full Bluetooth with OEM steering wheel functionality, rear

seat controls and OnStar still working like new.

E. Dash cam (matched Kenwood) for fighting traffic tickets and

dumb-*** drivers.

F. Rear view full capability camera (matched Kenwood) mounted

inside square steel tube located directly above receiver tube for

trailer hitch. (Makes hooking up trailers by yourself easier than

EVER!)

G. Sport tune by Black Bear (California) w/ AFM delete

165,xxx

A. Fuel pump

B. Carbon filter

C. Vapor canister solenoid

D. Throttle body

E. Fuel cap

F. MAP sensor

G. MAF sensor

H. Master cylinder

I. Injectors professionally bench cleaned

J. Pre and post cat o2 sensors

K. AGM battery

L. Serpentine belt and tensioner pulley

M. PCV hose

N. Intake manifold gasket

185,xxx

A. Professional through fuel rail carbon clean

B. Power brake vacuum booster

C. Fuel vapor purge valve

D. Active brake control sensor

E. Big alternator (I think it’s the 160 amp)

F. Active brake control valve (pump) assembly and module

193,xxx

A. Intake manifold

tech2

what is the fuel trim at idle and when held at 2500 rpm?
you changed the fuel pump...but has fuel pressure been measured?
flex fuel vehicle?

Ross R

Its running about 23% on each bank at idle (650 rpm), and It’s running right at 28% on each bank at 2500 rpm.
I borrowed a pressure gauge to check pressure before swapping the fuel pump, and it was weaker than it should’ve been, so I replaced with a new but stock Delphi unit. I have not rechecked pressure but can go get a gauge tomorrow and let you know.

Ross R

Oh and it’s not flex fuel, just regular gas.

Ross R

Okay, the fuel pump is pushing 60 psi . I was told they should be between 55-65 psi and the old was 44psi if I remember correctly.