Running on all 4!!

[wireguysny]

ok so gas up here in ny is like 5 bucks so lately ive been experimenting a lot with the way the cylinder de-activation works, ive got a good indication of how to muster out my best gas mileage...but heres my question..when its just me in the car and im not pulling the truck seems to run just fine on 4... so i started thinking... is there a way to program a chip or something that would keep the car in 4cyl mode. This would be awesome for city driving and when the car is empty on the morning commute. Since its in the software and automatic I assume this wouldnt be hard. I understand performance will be lost but I really dont care. I had an 83 bronco and after 100k miles it took 15 minutes to get up to speed..lol..so this doesnt seem to bother my...screw the overpriced hybrid, I think this would be the solution???

Anyone have any idea?

 

[Nnaboy]

I once thought about that, I don't think its possible but who knows?

 

[emann_01]

Ive said it before and i will say it again the edge evolution in economy mode gives about 2-3 more mpg

 

[Black Dog]

I do not think it could hanndle running on 1/2 the motor while under load. Just maintaining speed not a problem, but you're asking to break something with this idea. Also think about it if you were trying to get up to speed with a 4 cyl. it takes longer so you're on the gas longer and more throttle position, so it's still gonna burn a lot of fuel because it's not efficient. You still gotta have power to match the weight you're pushing. Same reason small blocks are not necessarily more fuel saving than big blocks under certain acceleration conditions, for example have a 300 hp 350 and a 400 hp 454 both pull the same truck to 65 mph in exactly 15 seconds each and you'll see the smaller one is working harder and burning more to do it.

 

[Gambler]

It may be possible, but it wouldn't save you any economy. The 4cyl mode would have to work so hard to accelerate the Tahoe that it would suck way more gas than the 8 would.

 

[kpanza]

You'll kill the motor in no time... one of the reasons it can't run on 4 cylinders for extended amounts of time is the heat problem...even though the engine is technically running on 4 cyls., the pistons and rotating assembly are still all cranking away...with no fuel being introduced into the cylinders, they still generate big amounts of heat...the motor will "cool" itself by running on 8 cyls more efficiently. Perhaps one of our tech savvy engine gurus can explain it better than I did? But I believe that to be the crux of the issue...not to mention that a powerful V8 under light load can cruise more efficiently than a 4 cyl under a heavier load at same speed...

Like was said, you'd likely use just as much fuel getting up to speed on 4 cyls as 8, if not more, due to the load...

About the only thing I think might be remotely possible would be for an electronics guy to somehow alter the "minimum throttle input" (for lack of a better term) settings to allow the motor to stay in 4 cyl mode for a little longer. What I mean is if you could cruise on the highway at slightly higher throttle inputs without it going into V8 mode? But let's be realistic, if it could be done to get significantly higher MPG, GM would have done this for us already...they know how strong a sales tool higher MPG is, so they would have tried to eke out every last bit of efficiency...but they also have to balance that against long term engine life...it would kill them if they achieved a 5% greater efficiency at the cost of engines blowing up in short order!

I guess bottom line is we all knew what kind of mileage to expect going in, and you just need to try to maximize efficiency by driving smartly...make sure your tires are properly inflated, you don't carry around any more weight than is necessary, you accelerate smoothly, you cruise at a constant speed in the sweet spot, trying for V4 mode as much as possible, etc...

 

[Gambler]

When I had my custom tune done he modified the v4 mode to take more throttle before switching to v8 mode. I think he said it was set at 12% throttle before...

 

[73shark]

You'll kill the motor in no time... one of the reasons it can't run on 4 cylinders for extended amounts of time is the heat problem...even though the engine is technically running on 4 cyls., the pistons and rotating assembly are still all cranking away...with no fuel being introduced into the cylinders, they still generate big amounts of heat...the motor will "cool" itself by running on 8 cyls more efficiently.

Although I've never witnessed it, a GM engr on another forum stated that the engine will only run in V4 mode for a ten minute cycle max and then go back to V8 to cool the cylinders. So I think kpanza got it right.

The only way I've been able to induce V4 mode in city driving is to use tow/haul mode when going up slight grades.

 

[wireguysny]

Well if it makes anyone proud ive been able to get an average of about 26 miles on my commute now setting the cruise control on 67 miles per hour here on the nys thruway. I didnt realize that the engine actually got hotter in 4cyl mode, its amazing the amount of technology involved. I guess I should have just paid more attention to my driving habits..its funny to see the difference on the needle from cruising to work at a good pace then to driving around queens last week stop and go...the needle looked like it was falling each time i stopped...lol... over all i love this truck, just going to buy a banger for the normal commute and treat myself to the Tahoe on weekends and special meetings.

 

[Gambler]

Well if it makes anyone proud ive been able to get an average of about 26 miles on my commute now setting the cruise control on 67 miles per hour here on the nys thruway...

This reminds me of a story my grandpa used to tell me. No wait, that was uphill both ways, sorry...

 

[ZX1100F1]

A couple of things on this issue that some people have hit around:
When in 4 cylinder mode the engine doesn't generate more heat, what happens is that the dead cylinders cool down after a few moments creating a thermal imbalance that can cause engine damage if left unchecked, this is why the 10 minute cycle.

The other thing is that the ECM has been painstakingly calibrated specifically to command 4-cylinder mode any time that engine loads allow and fuel efficiency would benefit from 4-cylinder operation.
In other words: If the engine is operating in V8 mode it is because the computer has determined that 4-cylinder operation will either adversely effect fuel economy or harm the powerplant.

 

[73shark]

Welcome to the Tahoe forum, Dave.

Saw it mentioned on another forum that factory programming is set at a 12% throttle increase to switch out of V4. Is that even close?

 

[AZSCTACO]

Welcome to the Tahoe forum, Dave.

Saw it mentioned on another forum that factory programming is set at a 12% throttle increase to switch out of V4. Is that even close?

I'm glad to see Dave came over from that "other" Chevrolet site He brings a ton of knowledge to us....glad to have him.

 

[Gambler]

12% is what Justin told me when I had my tune done.

 

[LAP TOP GAMER]

If you ran in 4 cylinder mode all of the time, you wouldn't really save gas as it takes a lot to move 5500LBS of mass, so I would just let the computer handle it as GM spent millions trying to prefect this technology.

 

[ZX1100F1]

Welcome to the Tahoe forum, Dave.

Saw it mentioned on another forum that factory programming is set at a 12% throttle increase to switch out of V4. Is that even close?

Thanks for the welcome.

As far as the throttle position to deactivate 4-cylinder mode goes: it is different based on each vehicle build but 12% throttle position is roughly in the range.

 

[73shark]

Then if mine shifts out of V4 mode going downhill or on level if I just barely move the throttle, does that mean it's not operating correctly?

As you know from our previous discussions, I've never thought mine worked right.

 

[Gambler]

12% throttle isn't much at all, are you sure you aren't pushing the pedal more than 1/10th the way down?

 

[ZX1100F1]

Keep in mind that there are many parameters that the ECM takes into account to determine which mode to select, if you are going downhill and you push on the gas pedal (even slightly) the computer interprets this as a call for more power and readies the system to provide an increase in available power by first returning the engine to V8 mode.


You are not alone in thinking the your Tahoe’s AFM system is not functioning correctly but I can (with almost 100% certainty) tell you that it is; the AFM system is designed to remain in V8 mode if it detects any fault.


The truth is that AFM will activate V4 mode less than 10% of the time on average, some people that drive with a light foot may experience better then 10% activation and some people may see worse, the system is intended to improve fuel economy roughly by 5%.