Haratchi

Hi all,

We have a problem with a brand new Corvette C7 Z06:
-The fuel can't be completely cut off, while the engine decelerates in case of downshifting !
-That's mean, the car then goes on with only a little bit of gas...after the downshift.
Any idea to solve this problem ?

Thank's a lot in advance for you help !

Mike

davepl

Why do you think it's a problem? The injector can fire about 0.3ms after throttle reopens.

The engine doesn't decelerate while downshifting. In fact it blips the throttle anyway so if anything adds power. But ignoring that, when the throttle is closed and fuel is cut off you're not making any power without fuel cutoff anyway so there's no power to be lost, no deceleration to be had.

Remember this is a direct injection engine, not a carb. You're not sitting there waiting for the accelerator pump to stroke...

Haratchi

We have two same brand new Corvette C7 Z06 with about 1200 miles.
One is OK and the engine brakes well when your food goes away from the gas pedal, but the second has this strange issue and the engine doesn't brake correctly........

blackrockets

Yes the problem is on my car, this problem appears only just after rev matching, the engine does not cut off during 2-3 seconds.

Nitro Vette

We have two same brand new Corvette C7 Z06 with about 1200 miles.
One is OK and the engine brakes well when your food goes away from the gas pedal, but the second has this strange issue and the engine doesn't brake correctly........



Haratchi-

If I'm understanding you correctly - your experience is that the engine will NOT decelerate AFTER you lift your foot off the accelerator?

Haratchi

Yes exactly ! Fuel cut off, but only after 2-3 seconds......after Revmatching !

davepl

Do you find a lag in general with the pedal? I do, whereas I did not on the C6 (which was also drive by wire). I did once have it on a larger twin-turbo car, so at first I thought it was forced induction but there's a tip-in delay too, not just on lifting.

Haratchi

No pedal lag, at least on my car ! Mine is 100 % OK !
I let Blackrockets answer this question concerning his issued car.
There is a noticeable difference, driving alternatively both cars !

ChrisN123

I have an A8 and have the same (or similar) experience-- but I figured it was a shift logic glitch. When completely off throttle, the car does not engine brake steady, but instead seems to modulate between a bit more and a bit less engine braking. It feels a bit weird. Maybe it is fuel injection thing....

Haratchi

That's exactly the description of the issue:
When completely off throttle, the car does not engine brake steady, but instead seems to modulate between a bit more and a bit less engine braking.

blackrockets

I did not see problem during break in the car because the problem occurs only when you drive it faster. And when you accelerate and shift up hard this is really a bad feeling because the rev do not go down immediately between the gears and this is like automatic gear box!

Nitro Vette

Now the question is - who's willing to take it to the dealer and explain what’s going on only to be disappointed with the outcome?

I have a feeling the root cause is in the GM ECU (engine control unit) and is correlated with engine/drivetrain longevity to survive the 5yr 100k warranty.

davepl

How would you describe it to the dealer? Even I don't fully understand the complaint (and I have an A8). When I took mine in this morning I asked about an A8 update flash (heard it mentioned on the board here) but they didn't know about anything offhand.

But again, what would be a crisp description to a service advisor (if one existed who could grok it)? I mean they're not going to change the code there, but I'd still benefit from a concise description.

gonabite

The PCM is still adding fuel. Now the question is does GM want to update the calibration or is intended to be that way. All you need to tell the dealer is exactly what it's doing.

davepl

I would imagine, when the topic Decel Fuel Cutoff (DCFC) in the Powertrain Control Module (PCM) programming comes up you're get the Labrador tilted-head look of confusion.

So on decel coast-down you feel the engine cutting in and back out? That is weird. I can't say I've experienced that, and my daily commite includes a 2 mile hill I coast down, though usually after downshifting to 3rd or so.

EngKoe

Hello,

The same "issue" is also mentioned in the european EVO article. Corvette Z06 versus .....GT3

http://www.m3forum.net/m3forum/showthread.php?t=497408


Koen

bryanh99

I tested this yesterday a couple of times on my M7 Z06. I do not experience this problem, the engine breaks very smoothly on mine. I will try some more today.