Hey guys i need some help. I m currently getting ready to do a turbo/nitrous set up on my 4.8L. As i am new to tuning the Ls computer I am trying to learn the computer by doing a stock tune. I am logging on hp tuners witch i used before to tune my 3.8 camaro witch had a turbo on and had great results. I got my wide band installed and tonight i went out and did some pulls just to see were the factory tune is, looking for knock and basically some base logs. Here is the problem when i go WOT my wideband tells me i am between 16.5-17 AFR. At first i thought my wideband sensor was bad or a wire was crossed but after reviewing my logs my narowband o2 are showing between 25-30mv witch would show a super lean condition. When i had my camaro turboed the narowband o2 would be in the 800+mv range matching the wideband. Everything else in the logs were ok only had a little bit of burst knock ( 1.5* after shifting ) other than that no red flag except for this AFR thing. I am wondering if anyone else has ran into this or is the computer just running a way that i am unaware of. Any input would be great and thank you in advance.

 

Are you logging commanded AFR to see what the computer actually wants vs. what it is actually doing? Are the PE enable tables still stock? What year is the computer?

 

No I didn't log the command AFR ( i feel stupid ) Computer is a 2000 and all tables are bone stock.

I just looked at the stock tune and the tune should be commanding 11.8 at wide open throttle after 3600 RPM super rich but sounds right for a factory tune.

 

You might not be going into PE mode. (Power Enrichment) If I remember correctly, some truck have a long delay before PE actually kicks in.

Look in the PE tab in the Fuel tab and see if there is anything like that in there. Also, if your MAP sensor is not reading correctly, that can also cause you not to go into PE.

Post up your logs and tune so we can take a look too. Also, what wideband are you using?

 

Here is a full second gear pull and the tune. i didn't have my wideband hooked into the computer for the this run but it was showing between 16.5-17 AFR

 

You need to check your fuel pressure. My guess is the fuel pump is shot.

Only the HD trucks had the PE delay to my knowledge.

 

1500's had PE delay also, I can't say for sure if they all did but I know at least some of them have it.

Although looking in his tune it appears his only has a RPM delay.

 

Which models? Were they 6.0L tunes? Just asking because I've looked at a lot of stock 1500 tunes and none had PE delay.

 

PE delay doesn't explain AFR of 16.5 anyways. Weak fuel pump until proven otherwise.

 

pump is a racetonix 255 unit out of my camaro only 2 years old. Fuel pressure gauge is showing 72psi at wide open throttle according to my fuel pressure gauge. now maybe this has something to do with it. i looked up gm spec for factory fuel press. at idle i am seeing 68psi. gm spec is a max 62psi. Whats the best way to check the pump, i have no problem double checking the pump. i went over the motor looking for a vac leek but i couldn't find any leeks. A vacuum leek would enplane the lean condition but were would i find a leek that big?