C7 cylinder deactivation

[RussTeens]

Keith at Eurovettes carried out a re-programme of my 2017 GS Auto at the nationals specifically to disable the cylinder deactivation. This was due to the constant swapping to 4 cylinders even at low speed, really annoying. I also have little confidence that driving a car on 4 cylinders in the long term is good for the engine. Lets not forget the only reason this technology was developed was to fudge the MPG and emissions figures to increase GM's overall MPG average across the whole range.
My car is a US import so the deactivation was aggressive. Since the alteration the car feels smoother during acceleration through all gears, pulls better from low speed as there is not the momentary heistancy whilst 8 Cyl's come back on line, and the fuel consumption has only decreased by approx 1 mpg, which I can live with.

The remap is reversible, Keith kept a copy of the original programme/tune.

Can see how that would be annoying. When in 4th at 30 to 40 mph on smaller roads, mine would swap to 4 cylinders so I tend to swap into touring mode most of the time which on my car deactivates the cylinder shut down. It didn't feel right to me it cutting in out out all the time. I can see how on an auto or US spec car that would be really annoying. As you say 1 mpg is not really worth worrying about. I'll have a play next time I'm on a motorway and see what difference it makes.

 

[Roscobbc]

That's interesting. Keith has been a long term Corvette "good guy". Given he's been selling one or two US market C7s in UK it's interesting that he's not advertising AFM delete on the forum as a service. I guess if it's done as a paid service that can open up a whole Pandora's Box of potential liability issues, given some engines appear to have failed in this way after AFM delete. (That's also my guess of why Ian Allan don't do it.)

If it ain't broke (or at least 'partly' broke) as a 're-programmer 'don't fix it and potentially land yourself other unreleated issues?

 

[teamzr1]

Since I started keeping records via my custom tuning process, saved just about 10,000 OBD2 scanner recordings I analyzed

Not one going back to late 1990s GM vehicles, most of them F & Y body has had engine problems when I turned off DoD/AFM
Very simply, the PCM (engine controller) believes the engine does not have DOD so is not commanding any of its functions
thus the engine valve train functions as they always have pre DOD/AFM

 

[UKBeancounter]

Ian Allen are official GM / Chevrolet Europe sellers. Given that any ECU alteration usually invalidates the warranty I am not surprised they don't want to touch things.
Not read anything about engine failures after AFM delete, only the GM service/recall notices on what dealers should do when lifters seize in the head due to AFM malfunctioning. If its going to blow up, its going to blow up !

 

[Rich]

Not a Corvette, but I have had an AFM disabler on my Camaro for 3 years. Same engine as the C7 but different gearbox. Wouldn't be without it. The vibration through the transmission is noticeable when it is unplugged. Fuel economy is irrelevant and minimal anyway

 

[teamzr1]

GM even does not want 4/8 cyl crap
Notice on Z06 and ZR1 engines do not have DOD/AFM as already have to pay a gas guzzler tax
so it is clear it is all about games as to federal MPG mandates and politics

If you drove through areas where the elevation changes up/down are or at higher elevations where engine performance output is less
would you want to do that with one 1 or 2 legs
Same thing with DoD/AFM changing loads onto auto tranny
where Hp/Tq is half, but the mass going up hill is worse as load

 

[Digger John]

In my euro spec C7 Grand Sport the AFM only operates in Ecco mode so i run in touring mode all the time for general driving so never switches to V4 mode.

 

[mickn]

In my euro spec C7 Grand Sport the AFM only operates in Ecco mode so i run in touring mode all the time for general driving so never switches to V4 mode.

This is exactly what I do in my '18 Grand Sport

 

[Rob59C1]

I can see this issue has been well covered but I'd just like to be sure about something. I have a 2014 Z51 manual euro spec which as has already been said, only allows cylinder deactivation in Eco mode, so is easily avoided. However, I'm now considering a US spec Auto. So my question - is cylinder deactivation always on in every mode for 2019 Stingrays, Z51s, & Grand sports unless modified?

 

[Chevrolet]

I can see this issue has been well covered but I'd just like to be sure about something. I have a 2014 Z51 manual euro spec which as has already been said, only allows cylinder deactivation in Eco mode, so is easily avoided. However, I'm now considering a US spec Auto. So my question - is cylinder deactivation always on in every mode for 2019 Stingrays, Z51s, & Grand sports unless modified?

Not sure why you asked the question Rob? Per "Stingray" above, US cars can go into AFM 4 cylinder running in all drive modes, including "Track". I'm not aware that was changed on 2019 or later cars? So options to get rid off that look like the Range Technologies plug in device, or a remap like the one Keith did for UKBeancounter above?

 

[Rob59C1]

Not sure why you asked the question Rob? Per "Stingray" above, US cars can go into AFM 4 cylinder running in all drive modes, including "Track". I'm not aware that was changed on 2019 or later cars? So options to get rid off that look like the Range Technologies plug in device, or a remap like the one Keith did for UKBeancounter above?

Just checking that it applied to 2019 models as the experience of the contributors to this thread don't or didn't have 2019 C7s that's all. If I'm going to splash out on a 2919 I need to understand & be sure of all the implications. Due diligence & all that! BTW does it really apply to Grand Sports with auto transmission too, as per my question?

 

[Chevrolet]

BTW does it really apply to Grand Sports with auto transmission too, as per my question?

Yes, UKBeancounter's car above is a US spec Grand Sport.

 

[Rob59C1]

Yes, UKBeancounter's car above is a US spec Grand Sport.

Thanks, although his is 2017 so still not totally sure it applies to 2019. which is why I asked for confirmation. Just hoping GM came to their senses. Especially with a GS & a Z51, which are aimed at track use. I guess their rational was, on the track use the paddles, hence no deactivation with manual selected?

 

[UKBeancounter]

Rob, I am not aware there were any significant alterations to the Grand Sport between release in 2017 and 2019, other than the Diff Oil being altered which reduces the issues caused by the AFM. I have not had my oil flushed and replaced with the later spec oil but will have this done at the next service. I have not had any issues since the ECU reprogramming, the C7 definitely runs smother and is more responsive when running in V8 mode only.
Jason

 

[Rob59C1]

Rob, I am not aware there were any significant alterations to the Grand Sport between release in 2017 and 2019, other than the Diff Oil being altered which reduces the issues caused by the AFM. I have not had my oil flushed and replaced with the later spec oil but will have this done at the next service. I have not had any issues since the ECU reprogramming, the C7 definitely runs smother and is more responsive when running in V8 mode only.
Jason

My Z51 being manual & EU spec only cuts in in Eco mode. I have tried it a couple of times on flat stretches of motorway with virtually no load on and it's fine but wouldn't consider running it for normal driving which is, as I now realise, the case with a US auto. Seems crazy they don't restrict it to Eco. Who the hell wants to run on 4cylinders on a track?

 

[teamzr1]

I am the one that tuned DOD on that 2017 GS in July 2023, ending VIN # of 3802

FYI
Here is how a 2014 C7 with manual tranny is set by GM within the PCM Calibration

CALIBRATION PARAMETER REPORT By : JR - Team ZR-1
Source File: C:\CS6\14C7M7\AHMED.cal
Print Date: 10/4/2025

Displacement on Demand

DoD Enable ERT 45 Sec.
DoD Disable Vehicle Speed 5 MPH
DoD Disable Vehicle Speed Hysteresis 1 MPH
DoD Enable Vehicle Speed - in P/N 5 MPH
DoD Enable ECT 36 Deg. C
DoD Enable ECT Hysteresis 4 Deg. C
DoD Disable_RPM 3200 RPM
DoD Disable TPS 50 %TPS
DoD Disable TPS Hysteresis 2.5 %TPS
DoD Disable Brake Vacuum 0 kPa
DoD Enable Brake Vacuum 0 kPa
DoD Disable Low Oil Pressure 25 psi
DoD Disable High Oil Pressure 68.2 psi
DoD Disable Low Oil Temp 18 Deg. C
DoD Disable High Oil Temp 130 Deg. C
DoD Disable Low Ignition Voltage 1 11 volts
DoD Disable Low Ignition Voltage 2 11 volts
DoD Disable Low Ignition Voltage Hyst. 0 volts
DoD Re-enable RPM 3100 RPM
DoD Low RPM Limit Hysteresis 475 RPM
DoD High RPM Limit Hysteresis 200 RPM
Min. DoD Off Time 3 Sec.
DoD Fuel Cutoff Enable Delay 3 Sec.
DoD Delta Vacuum Test Enable Time 480 Sec.
DoD Max. Time 600 Sec.
DoD Disable Pos. Delta Vacuum 5 kPa
DoD Disable Neg. Delta Vacuum -5 kPa
DoD Min. Re-enable Time 60 Sec.
DoD Disable Oil Aeration RPM 3100 RPM
DoD Disable Oil Aeration Time 5 Sec.
DoD Disable Oil Aeration Reset RPM 3000 RPM
DoD Disable Oil Aeration Reset Time 50 Sec.

DoD Enable ERT Vs. Engine Off Time

Off Time (Sec.) ERT (Sec.)
0 20
5 20
10 20
30 20
60 20
100 20
120 20
140 20
160 20
180 20
240 20
300 20
360 20
420 20
600 20
700 20
800 20

DoD Disable Vs. Selected Gear

Gear
D1 1
D2 1
D3 1
D4 1
D5 1
D6 1
D7 1
D8 1
Neut. 1
Rev. 1
Park 1
T1 1
T2 1
T4 1
T7 1
T8 1
T11 1
T13 1
Illegal 1
Transistion 1

DoD Disable Vs. Gear

Gear
1st 1
2nd 1
3rd 1
4th 0
5th 0
6th 0
EVT 1 1
EVT 2 1
Neutral 1
Reverse 1
Park 1
Reserved 0
Reserved 1

DoD Low RPM Limit Vs. Gear

Gear RPM
1st 900
2nd 900
3rd 900
4th 900
5th 900
6th 900
EVT 1 900
EVT 2 900
Neutral 900
Reverse 900
Park 900
Reserved 900
Reserved 900

DoD High RPM Limit Vs. Gear

Gear RPM
1st 2900
2nd 2900
3rd 2900
4th 2900
5th 2900
6th 2900
EVT 1 2900
EVT 2 2900
Neutral 2900
Reverse 2900
Park 2900
Reserved 2900
Reserved 2900