Hi Guys,

As most of you know, I put a LT4 396 in my 96 corvette.

It is running "good" ( there is always something that needs more work...)

I have been trying to do some fine tuning while breaking it in. Hopefully, the first of next month I'll be ble to stick the supercharger back on it....

What is driving me crazy is the LTFT's are really whacked...

At idle Bank 1 I'm seeing 7.8% and bank 2 -15.6 % the STFT's are 0 % and - ~ -10% respectively

At 1200 rpms LTFT is 0 and -15.6%

At about 2000 rpms they run at about -3.1 (LTFT) and the STFT's at 4.7

Here's what I have tried thus far... :

Swapped injectors,
swapped throttle body,
checked headers and exhaust for exhaust leaks...
double checked AIR hoses and connections
Checked vacuum lines...
Checked EGR...
Swapped PCV valve,
new opti
New igniton wires
new plugs ( stock heat range)

I'm running through the stock accordian and MAF ( which is currently disconnected)

I have swapped around the o2's, but I'm wondering if they may be shot, they look ok on the logging software...

Right now if I connect the MAF it drives bank 1 further positive +25 / -13.8 and starts misfiring on the left bank.... and was causing the bank 1 cat to start glowing... fouling the left bank plugs.

Without the MAF connected it idles smooth and runs extremely good... (aside from the trim difference) The throttle response is very good...

I've sprayed around the intake but everything seems tight... no vacuum leaks that i can find...

I have LT1 edit... since I'm not running the MAF could it be that the VE's are off because of the cam? ( lunati 214 / 228 @551 lift) I reset the ECM to see the proper injectors and the proper displacement... ( wondering if it were raised or lowered if it would skew in one direction or the other)

I'm used to adjusting the MAF and PE side of things ( in the past) but I really never touched the VE settings before... they show the KPA and RPM settings with the percentage of efficiency... ( which I understand)

Can some one give me some insight as if i increasing or decreasing the efficiency will it drive the fuel trims up or down...?

If I were to increase or decrease the fuel either by injector offset or through the MAF settings is there a chance of anything getting the numbers closer? I have never seen them this far apart...

Is there something I am overlooking? Is there a chance I need to reinstall the intake?

At WOT the o2's ( which are along for the ride) are running like 880 / 860 which is not too bad about 2% difference...

Thanks in advance...

MO

 

Mo, this is just a thought, do you have anyone near you that has a four ofr five gas analizer? if so you should be able to use it to check for small exhaust leaks, it sounds like you have a intake manafoild leak or a exhaust leak that is makeing your O2 on that bank to read wrong.
my bet is on a intake leak, we had one (not a vette) in the shop not to long ago that had a intake leak under the intake that was closed up so that it was sucking air from the crank case and not from out side and all of the standard ways of checking it came back negitive.
Just a thought, Greg Nettles

 

Mo is there any chance that you have any exhaust leaks near the O2 sensors. Also try swaping the O2 sensors from bank to bank. That will let you know if you have a sensor issue. Something is telling the O2 sensor that the bank is lean and the PCM is reacting by adding fuel to the LT trims. The O2 sensor is the final control element, it has final say in how the PCM will adjust the long term fueling.

 

blown87,

Thanks that is what I'm wondering... I installed the intake while it was still in the engine stand... so I know the end silicone had plenty of time to "cure"...

Hey TJ, No, I haven't swapped bank to bank... I'm going to go out and buy new O2's today...

If there are any exhaust leaks they have to be really small .. I have this thing locked down like fort knox... I recall having worse leaks with the 350 and they were not that far skewed.

I should probably replace the O2's anyways... If this doesn't resolve it. Then I'm going to replace and reinstall the intake again maybe somehow it slid... the bolts all went in fine... "who knows" ... HEH

Thanks for you input!

MO

 

Mo, if you have a infrared temp gun you may be able to check the header pipes and see what the temps look like, i would think if you have a cylinder running lean it would be hotter than the rest. good luck with it

 

Mo,

where are your O2 sensors? are you running long tubes with them near the collector? if so I had this exact same issue.. could not get one of my collector flnages to seal just perfect and it ultimately caused the bank with the leak to go so rich it covere the bumber in soot and mileage went to ****.

I finally ended up using a temp probe to make sure that all cylinders were burning the same and had close EGT's and then moved the drivers side O2 sensor to the bung in the header primary of the hooker long tubes which was for the stock location of the TPI O2 sensor... reset the PCM.. and took it easy for a few miles and cleaned the rear bumber.. gave it a chance to settle on a steady fuel trim and voila everything went back to normal no more sooty humber.. mileage came back, changed the plugs and eveyrthing ran smooth as silk.. so even if the leak is after the O2 sensor.. it will still pull outside air in between pulses causing the O2 to reak havoc on your LTFT's

let me know if this may be a similar issue? if it is you may consider going to a V-band flange and couplers at the collector to exhaust.

Chris

 

Hi Blown,

Yes I have a IR temp gun , that is a good idea...

I've also wondered about the injector balance settings... but I don't have the thermocouple to chec the balance, I was thinking it could be possible to do it with the IR temp gun but I was concerned about the accuracy as well as add another potential varible to deal with.

Icevette,
I am running shorties, the O2's are in the stock area I'm using the Random Technology Cats, and Corsa exhaust... I'm not 100% sure that I'm not sucking some air in through the A.I.R. I'm going to plug them at least temporarily to eliminate that variable as well.

I just bought new O2's to eliminate the possiblity that they are "poisoned"...

Just for posterity sake I may pop off the intake as well if anything to be sure that it is sealing properly. OnceI put my supercharger on I want to be sure I have all of this stuff "wrung out"..

Thanks !
MO

 

Greg,
That's what it was... the intake was not fully seating for some reason, couple hours and a gasket I should be back in business

Thanks!

MO

 

i am glad you got it going, make some tire smoke for me
Greg Nettles

 

I have balanced trims now... they were showing -15.6 but that is cause I put my #36's in again and the ecm was set for #26's so HOPEFULLY I can start getting this thing dialed in....

Mo