High LTFT and Misfire
 

My car has a problem with misfiring when it starts cold, always cylinder 4. HPtuners shows it misfires around 80 times, and then once the idle dies down it mostly stops. However, anytime I let off the gas from light acceleration, cylinder 4 misfires twice. I have a few other cylinders that misfire a few times but I understand that is mostly normal.

I also noticed that my LTFT reads pretty high, anywhere between 15-25%. I got P0171 and P0174 codes while driving the other day, about 20 miles after I used the CRC intake cleaner. I have a log from a few months ago where it showed my LTFT being between 0-5%.

I have tried the following to fix it:
Cleaning the intake with CRC intake cleaner
Swapping the coil packs and wires between cylinder 2 and 4
Bottle of techron fuel cleaner in the tank.
Spraying small amounts of ether around every vacuum line I can find, but no surges or changes on idle when I do it
Cleaning the MAF sensor with CRC MAF cleaner

At this point I'm not sure what the problem is. Someone said it could be an 02 sensor that got dirty after using the CRC/techron, but the o2 sensors still read as normal when I compare recent logs to past logs. Could it be a bad injector?

Mods: E85, GM CAI, Borla Axleback

List your mods-it may help to troubleshoot.
Try a fresh set of plugs.
It could be an injector-if you don't have any vacuum leaks, that could be the cause of your misfire and your high fuel trims.

I knew I forgot something. I edited my post with the mods.

So even if I have 1 injector that is bad/failing, it would cause high fuel trims on the other bank?

Also, when looking at the car from the front (cooling reservoir on the left), it goes 2, 4, 6, 8 with 2 being the closest to me, right?

Firing order/cylinder layout. Except that the firing order is : 1 – 8 – 7 – 2 – 6 – 5 – 4 – 3

Perfect, that is what I thought it was but I figured I'd ask just to be 100% sure.

So on the injectors, if 1 is bad it can cause both banks to read as lean?

Unmetered air entering the system can cause false positive fuel trims. Check all your connections between TB and Maf.

What’s your alcohol content reading currently? If your flex sensor is not working correctly it would dump around that much fuel.

My fuel trims were about 17% high when I took my car to the dyno. I thought that maybe my wideband or O2 sensor was bad. After talking to my tuner and sending him my dyno logs he informed me that I needed to go to a 95mm TB as my current TB (Solar 87/91 ported) was causing it to pull vacuum and running rich. I have currently swapped out the TB for the 95mm and working on the new tune. Hopefully that takes care of my rich condition at WOT.

Did you ever figure out the issue? My car is also misfiring on cylinder 2 only when I’m on E85. Have headers, manifold, X pipe, intake, tune. Just ordered a 95mm TB. During logs, my TB only opens to around 56% during WOT.

I retuned it and all is well.