Lean code and fuel trims... What do they mean?

[Waffleofdarkness]

Ive been fighting a LEan code for both banks pretty much since I bought this darn thing... Its a 2000 4.0 sohc automatic. I tried a new fuel filter and fixed a vacuum line that came off, and nothing. When its cold it idles at around 500 rpm and its shaking and it feels like it wants to die but it never does. This probably isnt related, but When I first start it in the morning theres a creaking sound that comes from the engine only while the starter is engaged, like cold metal on metal almost. The starter is a recent re man. Anyways I reset the light and then I had my scanner on the truck and I took a freeze frame when the codes triggered. Its been a couple years since my apprenticeship so I cant really remember what fuel trims represent, but Ill post them and maybe someone can point me in the right direction:

(In closed loop)

ECT = 73 (celcius)

STFT1 = -0.8%

LTFT1 = 5.5%

STFT2 = -2.3%

LTFT2 = 2.3%

RPM = 1547

VSS (kmh) = 48


Is that of any use to help point me in the right direction? For some reason Im thinking the fuel pump is getting weak but I could be wrong

 

[2000StreetRod]

fuel trims

Your fuel trims are not that far off at cruise. Why do you think you have a lean condition? With those trims no lean DTC should be set. The SOHC V6 is notorious for leaking intake manifold gaskets. They dry up with age and shrink allowing unmetered air to enter the cylinders. As the engine warms up the gaskets expand reducing the leakage. Also, a small air leak at idle may be significant but not at cruise when there is a much larger engine airflow. Have the upper and lower intake manifold gaskets ever been replaced?

 

[sgully67]

It's a good bet that 2000StreetRod is right about it being the intake gaskets. If you are getting lean exhaust codes look at the freeze frame data with a scan tool and you'll probably see that the code is setting at idle speed. Easiest way to know where the leak is is to use a smoke machine on the intake system to see where the leak is. You can also use carb cleaner. Spray around intake and the idle will increase when the leak is found. Be careful with this method as hot exhaust or any spark leak can cause the carb cleaner to ignite.

 

[Waffleofdarkness]

Ive got 2 DTCs for lean codes, bank 1 and 2. I actually sprayed some
Brake cleaner around where the upper intake meets the lower, its definetly leaking there and there is a noticeable gap between the parts. Im
Hoping that does it