For reference: 2014 C7 Z51 A6 with an A&A centri kit, and test pipes.

For the past year I have been having an intermittent issue where the car will randomly stumble, start to misfire slightly and demand more fuel to stay running. Initially the car would die and I could restart it and all would be ok again. When it was analyzed more, the car was dying because the tuner had Long Term Fuel Trim shut off and the Sort Term would max at +20% but it was not enough. Since then the tuner turned LTFT back on and the car will not die but will take +50% fuel to stay running. This happens on both banks evenly. If this issue is occurring I can go full throttle and all will be ok at full throttle. I was initially reviewing the problem myself but took it to my tuner about a month ago and he was not able to fix it and he does not know anything. He even mentioned that he talked to the speed shops in Texas and no one had any idea what to do.

Here is what has been tried in order:
New O2 rear (initially had a cat and was getting a code aka a lean issue)
New Front O2
New Battery
Cat Delete
New Front O2 again
New MAF
Checked for air leaks and cleaned all engine grounds and frame ground points in the engine bay
Checked related fuses
Checked Spark Plugs, no signs of an issue, rechecked gap
100PSI Leakdown Check, All cylinders about 3% loss which is great
New HPFP (LT1)
Cleaned intake valves
Took it to the tuner and he rechecked all the basics
Ran the car in open loop mode, still had the issue
Reflashed the Car
New Computer
New High Pressure fuel sensor
New Injectors (LT1)

There are no codes other than related to being lean when the issue occurs. It is not believed to be a fueling issue as the pressures look good, no drop in low pressure or high. Due to running the car in open loop mode, it is not believed to be an air leak. My only thing left on the list is a random electrical issue of either shorting or broken circuit but again no codes to guide me where to look. The problem got more common as time went on and would happen on average about 20 min. Since the injectors, the issue has only happened once in about 2 hours of driving. I am open to any and all suggestions other than going back to stock, haha. Please help!

 

Sounds like you need a new tuner

 

How about posting some HP Tuners (or similar) data logs which include the event?

 

Gotta be a an issue with the tune. I would look for a reputable shop nearby and have them take a look at it. Preferably not the same ones who tuned it the first time.

 

lol...Ya think so?

 

The car was free and clear of the issue for the first 5 months of the tune which makes me think it is not in the tune. It is also so random and intermittent. I can only log at a 1hz rate but I can post the files later. I'm not sure there is any other tuner in the northeast. I think the next closest is ECS and they are 5 hours away.

 

Take a day or two and just get it handled. This brings back nightmares for me as I had very similar issues on a boosted S550 Mustang a few years ago. It stumbled and rough idled randomly. New tune cleaned it up.

 

This is the log from when an event happened. This was from when LTFT was still turned off. The event happens around line 375.

 

sounds like a grounding issue. I have seen random problems on computers from ad ground connections.it will have to be doing the problem for the tech to find it. Good luck!

 

The mass air flow sensor seems to have little relationship with the throttle position. Since you have already changed the sensor, I'd be looking at the sensor wiring or may be the sensor reference voltage. Is the MAF signal stable with the engine off?

 

Thanks for the replies so far guys. I have fully cleaned ground G100 previously, which is on the engine for the MAF, fuel system, O2 and basically everything else engine based. I cleaned a few other grounds previously as well. Today I cleaned the one in the trunk which I doubt is related but why not. I investigated the MAF and found a bent pin on the MAF extension that I got from A&A. I straightened it and reconnected it. I used silver sharpie to make sure it did not push the wire out again. This has happened once before and I had fixed it to no change in the car. I guess the tuner bent it again when they were checking things. Same story today with no change in the car despite fixing the pin. The weird thing is the bent pin was the Lt Green/White wire which is the MAF signal wire so I am not sure how it even functioned with a bent pin. After fixing it, the car still had issues. I will probably try to replace the MAF extension. I checked the MAF to Throttle relationship today and it looks ok. Part of the issue as to why the relationship is weak is that the recording speed for the logging is so slow. I will try and get a faster logger or remove some log variables to increase sample time. I have attached the log from when it went bad again today. The last two columns are calculated columns of the short and long term fuel trim and you can see it hits +60%.

 

So today I finally got another code which was AFM valve failures. Upon inspection I blew a fuse. Reading up on it, it seems like the valves fail open but I am wondering if the valves were closing when they were not supposed to, would it have caused this issue. I will leave the fuse out and keep driving it to see if the issue happens again. If it does not fix it I am wondering if there is something else related to the AFM or DoD causing this issue. Something weird like that makes sense as most of it is controlled by sensors and actuators and intermittency could exist. Does anyone think there could be an issue causing the valves to randomly close or the cam to be activating the DoD when it is not supposed to? My car has DoD disabled in HP Tuners.