I've been getting the codes for lean fuel for both banks. Usually throws the light after 60-100 miles. Using the torque app it seems, when highway driving, when I'm on the gas my ltft is good. When I let off the ltft goes up to 25 at times. I've checked the fuel pressure under different driving conditions and it is good at the rail. I also pulled all the injectors and they have good clean spray patterns. The MAF is new and clean, i cleaned the throttle body, what else would cause this? Another possibly related symptom is that sometimes when hit the gas from a stop, if i am light on the pedal, it will stall. Is this a tuning issue?
CK5
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LY6 lean fuel both banks
- Thread starter jdot2004
- Start date
Is this a swap? If so, who programmed the computer? whose harness? etc.
What is the fuel pressure? Does it have an original style airbox?
An exhaust leak upstream of the 02 sensors can cause this code.
08 6.0 swap. Psi harness and cpu. Had it dyno tuned thinking that may resolve this issue. Fuel pressure is 58. Cold air intake, not original airbox.
I did not find any leaks upstream of the 02 sensor.
Sounds like it needs some tuning for part throttle. Dyno tunes usually only address wide open throttle. A lot of the packaged harness/tunes have the wrong software programmed, they usually use whatever they have kicking around. I have fixed a few of them for my customers, the last one i did was a L99 swap and the computer that was sent had 6.0l suburban software on it.
Could be as simple as a fuel filter.
A vacuum leak in the intake can cause high fuel trims at idle/coast but good numbers under load. The computer fuels based on the MAF reading, so any unmetered air requires the trims to skew upward to reach stoich. Since you use so much more air under load and the vacuum is lower, the leak doesn't contribute as much. The LQ4s liked to munch intake gaskets and cause a leak underneath the intake. Don't know if the problem was fully fixed for LY6.
Fuel trims going lean when letting off the throttle sure sounds like a vacuum leak to me. The fact that both banks go lean at the same time tells me it isn't an individual injector or bank of injectors. You got to think what's common between both banks that would cause them to both go lean in high vacuum scenarios.
Could be intake gaskets. The plastic manifold could be cracked causing the leak also. One other often overlooked area we've come across is a leaking vacuum booster. Quick and easy way to check for the vacuum leak is to take carb cleaner and start fogging around the intake near the gaskets and under it with the engine running. When the RPM flares, you found the leak.
Could be intake gaskets. The plastic manifold could be cracked causing the leak also. One other often overlooked area we've come across is a leaking vacuum booster. Quick and easy way to check for the vacuum leak is to take carb cleaner and start fogging around the intake near the gaskets and under it with the engine running. When the RPM flares, you found the leak.
Thanks everyone. Had to put the truck aside for a minute due to news of having another kid. Appreciate the responses though. Going to try and spray for vacuum leaks again, hopefully this weekend. Will also try the filter/regulator since I have a spare. If neither, I guess I'll be having the tune checked.
Congrats on the new addition
Did not find any vacuum leaks and swapping the filter/regulator did nothing. Is there a way to check the brake booster to see if it is loosing vacuum. No hissing or anything but brakes are a little spongy. It is one of few original parts on the truck.
One simple way is to plug that vacuum port temporarily and see if the problem goes away
