TheGreat4.8

picked up a ls1 style piece at the dealer today and got it wired and fixed in the intake pipe but still have a lean knock,missing,surging,and a foul burnt smell at all rpm and load. but i could tell when i connected it the rpm would raise so that's good right?

I don't even have the turbo plumbed to the intake pipe just for safetys sake,
my fuel pressure is holding 40psi firm and i can't find any vacuum leaks at all around intake gaskets or hoses, nothing.

my 02's have less then 5000 miles on them and besides every time i burn them up the motor goes rich not lean, i experiment with my MAP sensor by pulling the wire off and the motor goes dead rich and stalls out.

do these MAPS go bad often and what are the symptoms of a bad MAP? I have the 2 bar gm 12580698 and its only a year old.

Oh and i had my codes checked with only one showing it was Code P0102 low mass air input or something, but that seems kind of irrelevant considering i have a SD tune...

KHester84

When the O2 sensors fail (assuming 0mV output) the pcm reads this as lean and adjusts the fuel trim to add more fuel, kind-of a "failsafe" operation. If you have modified the intake tract by removing the turbo, your VE table is no longer accurate, so your tune will have some error. I'm no expert, just started reading Greg Banish's book so let the pro's chime in

Has the weather changed recently? How long have you had this tune for?

Nuclear Endless

iTrader: (4)

SDs are meant for fairly stable weather, and they're picky with ANY changes to how the intake is set up, be it turbo, s/c, colder iat, warmer iat, altitude, anything can set a SD off to not work as well as it used to

TheGreat4.8

As far as the weather is concerned it was tuned last fall in cool pa air (its cool out now) and had a checkup/adjustment a few months ago, only reason i have the charge pipe unhooked is because i am waiting for a new wastegate and riding around NA like that is fine.

it drove fine like that for awhile but this problem has came all at once in a parking lot idling then just died, were talking about a serious lean problem across the board (barely drivable) not a small change.

The lean knock is strange to me, i can tell it's not a mechanical knock because you can feel that kinda knock. Isn't fuel injection suppose to correct errors and drive on?

Also i bought and tested a new MAF just in case but not any change at all, i think tomorrow i will try a new MAP

KHester84

Did you ever get this figured out? If you did have a bad MAP sensor, wouldn't you get a cel?

TheGreat4.8

I've narrowed it down to a set of collapsed lifters, i guess they are so bad they are making the knock sensors pull timing and also giving me this incredible miss and surge.

Ill be pulling the heads shortly to swap the lifters out with extras from another 4.8, i can only hope that my cam isn't down a lobe or two