What is "rattle mode"?

 

I am able to hold the rattle for an extended time by holding the throttle lightly between 1350 and 1500 RPM.

 

Ah, okay, I got it.

 

Sounds like it could be AFM.

"For Corvette Stingrays equipped with the six-speed automatic, Active Fuel Management is active in all drive modes until the driver engages the manual-shift mode using the steering-wheel paddles."

 

Möbius, you might be right. It sounds like it is coming from the engine bay, not from the rear of the car. I think it is time for a trip to the dealer.

 

I hope this does not sound like what you are hearing, but I thought I would give you the link just to cover the base. See video in post #123.
http://www.stingrayforums.com/forum/stingray-corvette-problems-issues/1950-some-issues-i-am-seeing-13.html

 

I have the same configuration (A6 non-Z51) and my AFM operation does not cause a "significant rattle" (or minor rattle) at any time. However, I do believe at the point and driving scenario you are hearing the sound is when the AFM is doing its thing. Coupled with the fact that you don't hear it when in manual shift mode when AFM is disabled, lends credence to it being something to do with the AFM function. Program your DIC to show when you are going between V4 and V8 to see if it coincides with the rattle noise.

As it is "consistent and repeatable", a trip to the dealer may be in order.

 

FWIW mine does the same thing, can only hear it when the top is off or the windows down and its not too windy. Sounds just like a header leak or cracked exhaust manifold. Only when its in V4 mode and you give it a little throttle where it wont kick back into V8 mode. Mine also does it any speed in that RPM range when in V4 under light load, if you are next to another car in traffic or a high curb you can really hear it.

I'm on my 3rd tensioner, it has done it since day one. The first tensioner leaked out all its oil it could around 1200 miles, then it would chirp when SWITCHING between V4 and V8. Replaced that one and the new one started leaking, third one hast leaked in 1000 miles so I guess its OK. But the ticking under light acceration in V4 mode hasnt changed a bit. Its a bit annoying at times, been up and down looking for exhaust leaks, since it only happens in V4 cant check it by just brake torquing it, maybe can lock it in V4 with the tech II or whatever they are using on these but so far I'm not that worried about it. Sounds like a 72 Ford van with a cracked exhaust manifold when it does it, but its still getting great mileage and sounds/runs fine in V8 mode.

GM has 4.5 years and 95,000 miles to worry about it, for now I'm not letting them fool with it. When it starts annoying me I just manual shift it, I'll probably pick up one of the Range technology things to stop it from going into V4 eventually once I find out they work OK on C7s.

 

I'm on my 3rd tensioner, it has done it since day one. The first tensioner leaked out all its oil it could around 1200 miles, then it would chirp when SWITCHING between V4 and V8. Replaced that one and the new one started leaking, third one hast leaked in 1000 miles so I guess its OK.

kp; Do you by chance happen to have on your repair ticket the part numbers for the tensioners that have been replaced on your car? You are the 2nd or 3rd person I've read about that have had multiple tensioner failures. I am trying to determine if GM has a new part for this problem, or if they are still using the original part for the fix.

 

It sounds exactly like a part I had replaced under warranty recently - a failed drive belt tensioner. It's a known issue and GM notice PIP5185A can be pulled up by the dealer and it's on a thread on this forum.

 

Rattle turned out to be the tensioner, SWO info attached with bulletin number and part replaced.

Sent from my iPad using Corvette Stingray Forum

 

Hi guys,

I had the same problem but now I have solved the problem with the noise in my Corvette!

It all has to do with AFM. (Active Fuel Management)

The sound occurs when the engine lies between V4 and V8 mode during normal and smooth driving
around 1350 and 1500 rpm. Then a self-resonance occurs in the drive belt that sounds like a clatter
in the engine compartment.

This is completely eliminated by deactivating "V4-mode" on the car. By connecting a software
(RANGE Technology "Active Fuel Management Disable Device") to OBD II
which blocks "V4 mode" and lets the engine run in "V8 mode" all the time, the problem disappears completely.

The car now runs more quietly, shifts more smoothly without beeping/ noises and provides a more evenly strong V8 power throughout the rev range.
I also took the opportunity to change the drive belt plus tensioner (Delco original see below) just in case,
for both have definitely taken a beating from these unnecessary vibrations that have arisen thus far.

Tensioner: ACDelco 12668977
Belt: ACDelco 6DK650

The fuel consumption then?
I'm completely screwed.
If I had wanted a car with a V4 engine, I would have definitely chosen another car!

 

You don't indicate the year of your C7, but noise from the tensioner was a common issue and replaced in early model years under warranty. The noise you experienced was more likely from the tensioner than the AFM system.