Eleventh Vette

Picked up our 2015 non Z51, 7-speed, standard exhaust last week. Have 500 easy miles on it and noticed an obvious stumble or misfire during light acceleration such as a slight hill in 6th gear below about 1600-1800 RPM. No check engine light. As a result really can't use 6th gear below about 70-75 MPH. 7th would be completely useless. Our 2000 and 2009 Corvettes pulled smoothly in 6th gear from 1000 RPM up. So far consuming about 20% more fuel than our 2009 used. Getting 23 MPG on easy country road driving versus 28 for same run with 2009. Best 50 mi average reported has been 27 MPG.

Tried both touring and sport mode, so AFM is not engaged. Checked all the plug wires. Anyone have this problem? Surely this cannot be normal.

Tried the eco mode on a 70 MPH level road and the switch back to 8 cylinders was so harsh, that I don't think I will be using it.

-CM-

Sounds like something is amiss with your car; what you describe is not normal.

Daemek

Have a 2015 7 speed as well, when going up a hill at all in 6th or 7th gear in low RPMS I do feel a hesitation which I assumed is normal so I don't press down on the gas at all in high gear, low RPM. Long as I don't push the pedal down very much in top gear I've never felt it. Far as gas goes, getting over 30 miles per gallon on highway and low 20's driving back and forth to work(stop and go).

Woodson

Those are really low revs. Sounds to me like you're lugging the engine.

WelderGuy

You've gotta be kidding.

Woodson

No. Granted I'm coming from high revving engines, and high torque cars are new to me, but 1600rpm in 6th going uphill seems like lugging to me.

KenHorse

1600 isn't lugging by any means. 1000, *maybe* depending on load but 1600? No way

Woodson

That has to be. No? Right from idle?

mracer14

Nothing is wrong with the car.

Woodson

I just tried accelerating from 1600 in 6th gear on level ground. Nothing. I didn't even try it from 1000.

z51vett

There is a fix out for skipping and it involves un bolting motor mounts and moving it with pry bar do one side at a time. The skip does not set a code this is the strangest thing I ever heard of have written copy and photos showing how.
z51vett
Doug

WelderGuy

Does the "fix"have an official GM name and number? It's hard to imagine how changing the stress on the engine mounts (or whatever that fix does) would affect the OP's problem with the engine misfiring.

lastcowboy

try checking your inj. conections there was a post on here they found
one to be loose and out of the conector . hope its that simple for you.
they have also found loose s.p. wires . good luck

z51vett

Here is all that I have right now.
Rough Idle or Vibration
October 8, 2014
On some 2014-2015 Corvette, Silverado, Sierra and 2015 Tahoe, Suburban, Yukon, Yukon XL and Escalade models equipped with the 4.3L, 5.3L or 6.2L engine (RPOs L83, L86, LT1, LV3), there may be a condition of a rough idle or a vibration at idle in gear. There will not be any DTCs with this condition.



To correct the vibration, perform the following motor mount alignment procedure.



1. Loosen the engine mount bolts at the frame attachment points. (Fig. 15)



F15 3955251 mount bolts

Fig 15



2. Lift the engine slightly to take the load off the mounts.



3. Use a pry bar to push the mount outboard as far as possible (about 1–1.5 mm) (Fig. 16, left engine mount; Fig. 17, right engine mount); torque the bolts while pushing the mount outboard.



F16 3940842 left side

Fig 16



F17 3940843 right side

Fig 17



4. Tighten the center/upper bolt first, then front, then rear (Fig. 18). Complete this procedure for both left and right mounts.



F18 3955249 bolt 2

Fig 18



5. Lower the engine.



The vehicle may need to be driven for some time to confirm the condition has been eliminated.
z51vett
Doug

WelderGuy

Ahh. The fix doesn't do anything to the engine itself. It just keeps the vibration from being transferred to the car's body through the engine mounts.

It doesn't sound like that's the OP's problem, since the fix only applies to vibration when the engine is idling.

lastcowboy

Boy....you have to be kidding .😨 guess we would have been better
Off ordering the car un
built and put together ourselves .
Good luck hope you don't have to replace the mounts.

stevedun

Mine does the same on hills. I think it is just a little low RPM to not lug a little in the higher gears going up hill. I think I only needed a 5 speed.

bob guzzy

I checked everything, I could think of, I had it back to the dealer because I had a check engine light on from screwing with the exhaust flaps, I was hoping they would find the miss, no way.

I went through the trouble of putting a new set of NGK's in along with a cheaper set of plug wires just to make sure it wasn't wires, (they did ohm out right but I wanted to see for myself if the wires made any difference.)

Since installing the Diablo ITune's, Diablo tune and eliminating DOD my car is much improved.

Don't bother changing the fuel you use, don't change the plugs or wires, I did all of it including running it in all modes, my guess is I put on 1500 useless miles looking for this problem.

Here is what I think is happening, when you step into it for power, the computer is shutting down cylinders.

When you gain mph you overcome the miss just like any car would with a dead wire or plug.

WelderGuy

That makes no sense at all. Why would the computer shut down cylinders when you're calling for power. That just puts more load on the remaining cylinders.

The only reason to shut down cylinders when you're calling for more power would be detonation, but they can control that by retarding the timing or adjusting the mixture.

Maybe they just need to add a "downshift-needed" alarm so you'll be forced to keep the engine well up in rpms to keep the engine happy.

You gotta admire their response...anything they can't figure out and fix is "normal".