I returned from an 800 mile trip over 6 days and after my first fuel up away from home the engine and exhaust started acting strange. I have gone through that tank of gas and added a fuel system cleaner to the next tank, and have since went through that tank. At one point I had a check rear axel light, check stabilitrak light, and a check engine light on all at the same time. This came on twice after two separate restarts during a 15 min period and never came back on again. I did have luggage in the trunk when this happened.

The car is still experiencing the issues listed below. Any help would be appreciated.

My Car:
2015 C7 Z51 A8
Mods: Mamo Throttle Body and Borla Catless Pipe

Engine Symptom:
- Fuel Injectors could be heard from both sides of the car while standing next to it at idle and much louder then normal. It sounded like a typewriter.
- Hesitation and lack of power when accelerating between 25 and 40mph and 70 to 100 mph

Transmission :
- Hard shifts between 1st and 2nd

Exhaust:
-popping while accelerating through a gear. This was in addition to the normal popping when downshifting and slowing down, and shifting gears while accelerating. This popping sound, sounded like it was coming from under the car and not the exhaust. It’s not a sound I have heard before and I leave the car in track exhaust mode.

 

As for electronics, how old is your battery? Can certainly be a consideration if original.

 

It is the original battery. It’s one of my suspicions too. Probably a good place to start.

picked up a yellow top Optima battery today and the car is acting better. Still sight hesitation in 1st through 3rd gear but much better then before. Going to let this tank of gas get to empty then add another fuel treatment to burn off any water from the bad gas.

any other ideas are welcomed!

 

It may be a bad valve spring does it act like it could be. You will know if it drops one. Robert

 

The car runs "okay" when driving normally and not spirited. By no means is this okay, but I did drive 400 miles on it like this yesterday to get home. What kind of symptoms would occur if it was a bad valve spring?

 

If you have done this more than not it is just the bad gas I dont see you going on the interstate 400 miles at 70 plus & it being a broken valve spring. More than not from what you are saying bad gas.

Let me say this also about bad gas IF YOU GOT A FILL up at a station AND that pump that you got it at JUST HAD gas put into it's tank and if it was really low ALL THAT NEW gas going into that tank WILL put all that trash rust & what ever all in the tank & you may have to chg out your gas filter in your car. THIS happen to me one time in my c5 took me for ever to fig it out & how I did that was chg out & did every thing under the sun. I cut open the filter it had just a ton of crap in it plus it started just after I filled it up also.. I also only put 93 in my cars plus go to the two here in my town that doesn't have the bad stuff in it.. Robert

 

Thank you for the response. Reading through that makes a lot of sense. Especially the part about driving the car on the interstate.

I did replace the battery with an Optima yellow top since the car is a 2015 and has 18K miles. I took it out this afternoon and it seems to be getting better but still showing symptoms. I will pick up a new fuel filter tomorrow. Thanks.

 

Go pick up a fuel filter for a C7 and swap it out real quick? Hmm, good luck!

 

Did you bother checking the codes to actually see what was wrong with the car? The fact that you have the CEL lit means something is going on with the engine and you need to make sure what you are doing is addressing the issue Vs guessing. There are other things besides bad gas and an original battery that could cause those symptoms. Given the length of the drive you made unless the battery had failed and was drawing enough current to pull the system voltage generated by the alternator down below a certain voltage it is doubtful the symptoms were due to a bad battery. If the battery had been pulling system voltage that low you probably wouldn't have made it home.

Bad gas or low voltage won't make the injectors make more noise. The CEL as I said before indicates the engine is having a problem. Check rear axle and service stabilitrack messages are generated when the engine has an issue where it can't deliver proper torque such as a misfire. It doesn't mean there is anything wrong with the the axle or stabilitrack but when the codes are checked you will probably see a code for each of those features that says the problem is with the engine.

First thing I would suspect is a loose spark plug wire. A loud popping while accelerating or loud noises under the car are probably misfires. If a spark plug doesn't fire when it is supposed to you will feel a lack of power maybe followed by a pop as the unburnt fuel flows from the cylinder into the exhaust system and explodes there instead of inside the cylinder. Loose plug wires can cause those symptoms. If you are having a solid misfire the code can tell you which cylinder to look at.

Bill

 

Bill is spot on. There has been more one case posted on this forum with the symptoms you describe. I don't recall any of them which were not engine related. I know several of them were loose or disconnected spark plug wires.

 

Thanks for the information. The CEL came on twice when I was in park along with the other two messages, but never have come on again.

I just returned from a long drive and all the symptoms are gone except for one. There is a slight exhaust flutter sound when I’m pushing it between 5 - 25mph. Other then that the car is driving like it was before this happened. In fact other then that problem it may be driving better.
Spark plugs/wires were going to be next to check but I may finish this last half tank of gas and see what happens. Thanks again.