25 mpg Silverado Z71

[Frank Lee]

"Does anyone know if Cylinder deactivation can be programmed into a computer program that does not have it??"

How would that work?

[bucknmusky]

I think, and I'm not completely sure, that GM's cylinder deactivation simply shuts off the pulse signal to the electronic fuel injection to certain cylinders to only fire 4 or 6 in a V8 depending on power requirements. the coils still fire a "waste spark" and the valves still open and close off the cam shaft lobes just like as if the cylinder was producing power with a fuel charge. I assume this is all computer controlled by the PCM (powertrain controll module) So if the computer can determine shift points, fuel injection pulse widths, fan on and off, etc. all based upon sensor outputs why is the power on demand cylinder deactivation not also able to be programmed ??
The pistons are still moving along with all other mechanical parts, there is no seperation so there is still a ton of wasted energy and inertia but for adding a few MPG on low load cruising it is worth it especially on trucks that are not always needed at full power.

[Frank Lee]

ya needz ta do more homework on that

[almightybmw]

I remember cylinder deactivation on my brothers old '89 bronco... lol idled great, revved great, but couldn't move the truck in 1st gear over a 3" bump on the dirt pad. Took us forever to figure it out, entire left bank was unplugged :P We were amazed it sounded so normal and ran at all.

I see no reason why you couldn't drop 4cyl on highway cruising. It only takes a micro second to fire up the down cyl's when the power is needed. I know my dad doesn't need all 496 ci for driving to work. Hell, that truck would drive fine with 6 cyl 90% of the time. It doesn't need all 320hp and 480ft-lbs on tap, only when pulling or climbing.

Someone should get aggressive with the cyl deactivation, and see if you can daily a 1/2T or 3/4T on 6 or even 4 cyl. That'd amaze me more than squeezing more hp/ci.

[taco]

u can hear the sound in dad's exhaust ,(it is an odd sound) before the displays says v4 mode. it also says at 65 on flat ground will go from 15-18mpg to 22-25 mpg( instant) on the display. i wish there was a ecco switch, where u could keep it off.
i have noticed it is not speed dependant but load. caus it iwll work from 20-80 mph(fast as i have had the gutless wonder)

[gascort]

Originally Posted by bucknmusky

I think,... GM's cylinder deactivation simply shuts off the pulse signal to the electronic fuel injection to certain cylinders to only fire 4 or 6 in a V8 depending on power requirements...

I don't think this is correct; pumping those "dead" cylinders with the valves still working would draw tremendous amounts of energy; I thought the reason we just now were seeing this cyl deac. technology was that valves can now be opened via solenoids to let dead cylinders "breathe", or something involving variable valve timing. Of course, I may be talking out of my arse...

[gascort]

Originally Posted by almightybmw

I remember cylinder deactivation on my brothers old '89 bronco... lol idled great, revved great, but couldn't move the truck in 1st gear over a 3" bump on the dirt pad. Took us forever to figure it out, entire left bank was unplugged :P We were amazed it sounded so normal and ran at all.

Sounds like my mustang - we ran out of cash when building it and I destroyed my oem camshaft so my buddy convinced me to put an F-150 cam in it. It runs pretty well, a good amount of power and torque, which I attribute to the truck specs, but last year (about a year and a half after fixing the car) I found out that two of the cylinders on the F-150 firing order are opposite what they are on the mustang, so I've got piston, ignition, and fuel events happening at one time, and valve events happening at another. I can't wait to see how much power and MPG I can get when I get a good cam for it.

[RH77]

I have never had much luck with cylinder deactivation in Full-Sized, V-6 cars: Impala, Monte Carlo. 3-cylinder mode (as indicated by the dash indicator) would hang on until the load built-up and cycled back into 6-cylinder mode. On the highway, this was quite cyclical at 65-70 mph and didn't show much gain at all in FE. Some engines were Flex-Fuel equipped, and allowed better performance of the AFM system with E85, but was entirely subtracted by the poor FE of E85.

(For the record, GM's "Active Fuel Management" is a mechanical process of manipulating valves -- it cannot be programmed if not equipped".

55-60 mph seemed to be ideal. The wind resistance was light enough to keep the load figures down and keep it locked-in as a 3-banger. Suburban-enviroment FE improved as well (~45 mph).

So, the trick with the pickup might be to monitor the load and figure out the parameters that it locks/unlocks. IIRC, the Imp factored a load of ~50-51% and full TC lockup. Reduce this through technique or mods could get you that elusive 30 mpg with the pickup.

-RH77

[Frank Lee]

I'm more than a little peeved with my F150. Went through the brakes so they don't drag, got new highway tires (slightly taller than stock) aired to 49 psi, mechanical fan delete, no idling- warm-up on the go, cruise at about 52 mph and what do I get? 14.6 mpg on tonight's fill.

[RH77]

Originally Posted by Frank Lee

I'm more than a little peeved with my F150. Went through the brakes so they don't drag, got new highway tires (slightly taller than stock) aired to 49 psi, mechanical fan delete, no idling- warm-up on the go, cruise at about 52 mph and what do I get? 14.6 mpg on tonight's fill.

Don't lose heart, Man. Are the temps, around the zero-mark or less? I've been getting really crummy mileage, as is usually around this time of year. With the winter fuel, crappy rolling resistance, longer warm-up times, lower IATs, etc. it's tough. Apply those techniques in warmer weather, and I'm positive that the results will be a heckuva lot better.

-Rick