OrionRain

2014 Vert (auto). Anybody ever figure out a fix for this? I try to drive mostly in manual mode so no switching, but am still seeking solutions.

Bill Dearborn

Dieseling is gasoline engine run on after it is turned off. How do you equate dieseling to what happens when the engine switches from V8 to V4 and back? I have an M7 that I run in Eco Mode most of the time. When my engine switches back and forth all I hear is a slight change in exhaust tone. It is barely noticeable.

Bill

OrionRain

Okay, call it pinging! It happens when I accelerate causing engine to switch back to V8 from V4 (2014 Z51vert auto). Engine makes dieseling noise (okay pinging) as if I'm using cheap gas. Happens with 93 octane in Jersey and Virginia. Never a problem if I'm driving the auto tranny in manual mode cause it locks in V8. Happens at all (legal) highway speeds. I've added gas additives from Chevron and STP (not in same tank) with no joy!

lakemg

Have you taken it to a dealership service department? Mine does not ping when switching. Do you have any audio or video of the sound to share here?

RKCRLR

Mine made a similar noise. Turned out to be the belt tensioner. Sounded like pre-ignition/detonation.

Bill Dearborn

Not trying to diss you. The problem is you need to describe the problem in clear words that other people recognize. It is difficult enough to communicate clearly when talking to a mechanic face to face but it is even harder to communicate through the internet when you can't wave your hands, make a sound or show a facial expression.

Bill

OrionRain

Thanks RKCRLR I'll check that out.

OrionRain

Yup! Sounds very condescending! So I'll drop in some "clear words" and professional descriptions you (AKA, Other People) may recognize and perhaps we can leave it at that!

What Is Engine Pinging?

"Pinging" is the metallic rattling sound an engine can make when accelerating. It usually occurs when the vehicle pulls away from a stop and the engine is under a lot of load.

Common Reasons for Engine Pinging

Improper Combustion Process
An engine can ping (or knock) due to an improper combustion process. A "spark knock" is the result of combustion occurring too early. Early combustion can occur from carbon buildup inside the combustion chamber, a lean air/fuel mixture, and advanced ignition timing (spark plug firing too soon). In a properly-firing cylinder, the spark plug ignites the air/fuel mixture and a flame front starts on one side of the piston and burns across the top to the other side, which creates a rapid and evenly-expanding gas that pushes down on the top of the piston. When the air/fuel mixture is ignited prior to the spark plug firing, the two flame fronts collide, causing the pinging/knocking noise.

eboggs_jkvl

Well, I know exactly what dieseling is (engine run-on) after shutting off the engine. I also know what pinging is. If you can make the darn car do it every time, get it to a dealer, have the mechanic ride along and demonstrate the sound. He might even hook up his testing equipment for the ride and use the actual event to help locate and fix your problem.

So, my recommendation: Go to dealer and have them investigate the issue. I assure you that there is nothing that anyone on here can do to pinpoint a v8/v4 noise issue. Usually problems of that ilk for the 15s, if it is an automatic, were transmission related. I've not seen anything in here on the 14s having a similar transmission problem.

I have the 2014 A6 like you and I've not come up on anything that even vaguely comes close to the issue you are experiencing.

Could be timing or engine problem.

I'm sure someone appreciates that splendid explanation of ping. Relax! No one is trying to make you look foolish but terms matter when trouble shooting.



Elmer

NSC5

The noise might also be from one or both of the AFM "sound changing" valves in the exhaust which are designed to provide a normal exhaust note when in V4 mode. A rhythmic rattling from one or both of them during transition could propagate through the exhaust system and cause a sound like a light combustion knock.

Bill is one of the most knowledgeable guys on the board so I wouldn't sell his advice short... He is definitely being helpful.

Bill Dearborn

That is a good point. I have a Z06 M7 and don't have the two valves that seem to cause problems for some people. When my engine switches from 4 to 8 to 4 all I hear is a slight difference in tone. ZsZsZs vs ZuZuZu which tends to disappear a second or so after the switch.

Bill

LSX Camaro

I have seen/heard this many C7's. Under certain driving conditions when the engine switches from 4 to 8 a noise that sounds like a Jake Brake can be heard from the rear. I have found issues with sticking valves in the exhaust, broken springs in the exhaust valves and the screw holding the arm on the electric actuator had come loose. I will say some noise is totally normal during the switching process. I don't believe it's timing, dieseling or pinging.

OrionRain

Thanks Sir, I appreciate. I'll check it out for these indications. Whatever is probably more annoying than damaging. Lately I just drive in manual to prevent switching. Take care.

TEXHAWK0

I always called the noise from running octane too low "clattering". I associate dieseling with the noise from engine that continues to run when ignition is shut off.
Glad I have a manual so it does not go to 4 cylinder mode unless I put it in ECO.

joemosfet

Could be your AFM valves opening/closing as they do when going from 8cyl to 4cyl mode.

Sometimes the car cycles them on its own, sometimes even at idle. First time it happened, it scared the **** out of me, I thought something blew out my engine and down my exhaust.

OrionRain

Yup Clattering! That's one of the things we called that sound back in the day. I've seen other forums commenting on their similar experiences (so, not trying to justify, but I'm not the only one with this issue). Regardless what it's called it's annoying! Dealer I bought it from assured me a couple cans of Chevron should end the problem. I'm probably gonna take it to Chevy and see what's what. Of course my stubborn Jarhead side wants to find and fix it myself (always worked with F-4s, lol)!

OrionRain

Thanks much Joe, I've also dug up some earlier forum comments crediting fixes to the Torque Tube, others the Drive Belt Tensioner Replacement - bulletin PIP5185.

I'm waiting for a nice day to drive over to Chevy. I'll let ya'll know what up. Thanks again, Scotty.

davepl

Since I'm feeling pedantic this morning:

- Pre-ignition: mixture ignites too early due to hot spots in the combustion chamber
- Detonation: mixture ignites all at once, usually due to compression from the flame front
- Dieseling: Engine continues to run after shutoff without spark due to hot spots, etc.

At least that's how I keep them separate in my head, three different things.

All that said, I've never once noticed my A8 switch modes. I've seen it on the dash (very rarely) but never felt it. You certainly shouldn't hear it, and I think the dealer needs to be involved. Doesn't hurt to go in with a theory though!

Cosmo Kramer

Or buy one of these and disable the silly AFM altogether. AFM, by the way, does help the car get any better gas milage (IMHO.) Rather, its a gimmick the auto makers use to reduce emissions to meet EPA (aka: Tree Hugger) standards. My '09 Tahoe with 120k miles started burning oil (one liter / 1k miles.) I bought the disabler, and my oil burning decreased significantly.

https://www.corvetteforum.com/forums...-disabler.html

Before I traded in the 'Hoe, I unplugged it. My Z is an M7 so I have no need for the disabler.

NSC5

I believe the current Range version works fine on the 2014 but there have been issues with the 2016 (and presumably 2017). I have a 2016 Z06 and after a couple of months of using the Range (ver 7.7) it set a DTC at startup illuminating the CEL and putting the transmission only into range 4 in drive along with disabled manual/paddle shift mode. Ver 7.8 was supposed to be the cure but it appears the problem can still show up. It isn't a deal breaker since restarting takes the transmission out of "limp" mode (put there because of a loss of communications due to the Range module).

I have been waiting to send mine in for an update. My Z06 has been parked for winter since late December but prior to that I have been using it in manual mode to avoid the annoyances of AFM. A Z06 goes into AFM mode far less often than the regular C7 but still enough to annoy me thus the use of manual mode and hopefully a properly updated Range module shortly. The extra problematic AFM exhaust sound control valves aren't used on the Z06; probably because they would quickly suffer heat death which has been a problem for heavily tracked non-Z06 Corvettes.

And Dave we have the same understanding of those three terms; it is the way I use them. Thanks for clearly delineating what each means.

Also see dieseling under the fun facts about top fuel dragsters http://www.sccoia.org/articles/top-f...er-fast-facts/