sounds reasonable if voltages not stable weird stuff is going to happen.

I'm having the same two codes pop up, I'm completely stock aside from a cat-back. I noticed my LTFT is in the high 30s at idle as well. I'm taking her into my buddy's shop tomorrow so he can take a look. My question; Has this problem showed up anymore since you've replaced the battery?

Wow how creepy that you asked. Just a few hours ago popped P0171 for the first time since my original post. Looks like (and sounds) like a leak at the headers. Going to tighten them down and pray I don't need to swap the gasket :(

Fuel trims are high at idle and engine braking (20%) and the O2 sensor reads super high voltages when engine braking (dunno if that's normal but doubt it). Everything is normal when cruising and accelerating. Also, the car sounds really loud when you're sitting inside. I feel like this is all pointing to an exhaust leak that has been getting worse over time. I think that if the o2 sensor was dirty/bad I'd see high trims while cruising too, right?

I'll let u know what happens.

What are the trims while cruising and accelerating from low rpms?

LTFT appears to be between 30% and 40%. From what I can tell, during moderate acceleration, It barely dips. I didn't go WOT, but when I went slightly above 50% throttle, it dropped down around 10%.

Sorry to hear about that. I'm still trying to wrap my head around this whole concept. ECU programing has always seemed to confuse me.

if your seeing 30%-40% ltft something is definitly wrong\broken\leaking ect that level of trim is the limit of the ecu ability to try to correct afr imbalance between what the ecu is asking for and what its seeing from the 02 sensor.

get it sorted asap before it causes other issues.

That is the plan. I've arranged for rides until I can get my car to the dealer.

Someone I've spoken with suggested the fuel I filled up with last week (which isn't my normal fueling station) could be the culprit, or at least exaggerating the problem. In your opinion, how likely is this to be the case?

Bad batch of fuel or low octane fuel usually results in knock and some hesitation as ecu pulls timing to manage knock.

but unless yo fueled up with E85 by mistake you should not see fuel trims ltft of 30% plus

There's definitely hesitation and I'll admit that's it's been some time since I've really listened under the hood carefully, but it does seem louder and almost a muffled type of knocking that didn't sound like anything I've experienced. I know it's not unheard of that a tanker is filled with the wrong product and nobody catches it until after the fact. Lots of variables in that theory and I realize it's a bit of a stretch. Tuesday I'll be dropping the car off at the dealership.

Steve, around what voltage should the o2 sensor be reading when there's 0% throttle and in gear (engine braking)? Mine is over 4.2v, which doesn't make sense so that's why I'm thinking my headers are leaking now.

Try putting it in neutral and holding it at 1500, 2000, 2500, and 3000 rpm. I read that if your positive fuel trim starts going down closer to 0 then it's a vacuum leak on the intake side. Mine would go down from 20% to about 15% so I figure it's not a leak.

http://www.easterncatalytic.com/educ...agnostic-tool/

look at the front O2 sensor scaling in your tune you should be seeing about 0v at idle as this corresponds to afr of 14.7, it may vary around slightly especially on cold start.

http://www.ft86club.com/forums/attac...1&d=1424688932

look at the front O2 sensor scaling in your tune you should be seeing about at idle as this corresponds to afr of 14.7, it may vary around slightly especially on cold start.

you be better just looking at the AFR

http://www.ft86club.com/forums/attac...1&d=1424688932