Discuss! cylinder deactivation & GM's "skip shift" system

[Fummins]

Admin edit!

This thread split from...
Thread: Is it OK to skip the 4th gear to 5th for MPG?

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My Firebird came factory with a skip-shift "feature" that would force you to shift from 1st to 4th by locking out 2nd and 3rd. It was deleted before I got the car though. https://skipshifteliminator.com/p/wh...one%20normally. The more you know....


Shift blocking or “skip shift” is a feature of six-speed manual transmissions added to improve fuel economy ratings in the Corporate Average Fuel Economy (CAFE) system by preventing a driver from switching from first gear to second or third as would be done normally. A solenoid prevents the shifter from engaging these gears, forcing the driver to shift from first to fourth gear. The solenoid is computer controlled, and will deactivate if the throttle is opened wide enough, or the car reaches speeds above those typical in city driving.

[7milesout]

That may have been the dumbest feature GM has created.

[MetroMPG]

Au contraire! It was very crafty.

It was designed specifically to get the cars that used it a higher EPA rating than they would have otherwise had.

I don't think it qualifies as "cheating" either, because the EPA test methodology for manuals handicaps them somewhat. This probably just got the skip shift numbers closer to reality.

[7milesout]

Did you ever drive one?

[Mark]

That may have been the dumbest feature GM has created.

It would surely give cylinder deactivation some competition for stupid GM engineering.

I hate GM vehicles that have the auto stop & go feature that can't be turned off easily, too!

Most brands have lost my respect in the auto industry. On a positive note - If someone buys a new vehicle these days, I no longer suffer from any new vehicle envy!

[MetroMPG]

Did you ever drive one?

Yes! Skip shift had already been disabled.

I'd do the same.

But I still think it was a clever idea... that was meant to benefit the corporation, not the customer.

[Top_Fuel]

Yeah...CAGS (Computer Aided Gear Selection) was a pain on GM cars back then...but at least the customer could defeat it with a $10 part. Is there an F-body out there with a 6-speed and no skip-shift eliminator gizmo?

My 2003 Cobra had a T-56 and no CAGS. But I had to pay a $1,000 Gas Guzzler Tax on that car!?!

[AtomicPunk]

It would surely give cylinder deactivation some competition for stupid GM engineering.

I hate GM vehicles that have the auto stop & go feature that can't be turned off easily, too!

I actually think cylinder deactivation makes good sense in having the displacement available, but only using what you need situationaly. I was surprised to learn GM didn't invent it, and it dates back as far as1905.

Total agreement with you on start/stop tech, though. That is an obtrusive tech for trying to meet overly stringent CAFE requirements

[Pimp_Daddy_Patty]

A lot of these technologies seem to be a necessary evil due to CAFE and emissions. I do feel that they are good ideas at least on paper, but were executed poorly in some cases.

The most recent fuel saving method is to keep these engines at 1200rpm at all times because of automatics with anywhere from 6 speeds to 11 speeds. Good luck with passing or driving uphill though. That thing does not want to give you more torque to the wheels. This is part of the reason you see Hemis wiping out camshaft lobes and lifters, and why certain GM 4 cylinders seem to release the smoke prematurely.

As for cylinder deactivation. I'm skeptical about how well it works in real life. You still have parts moving and creating parasitic losses. I guess it helps keep the engine in a more efficient load range. That being said, my 94 Ranger had a 2.3L 4 cylinder, a 4.0 V6, and now a 5.0L Turbocharged V8. Most of these combinations have been used with 3.08 and 3.73 gears out back and each engine had a different version of the same transmission behind it. Highway fuel mileage has been 28mph for all engines. I guess you still need a certain amount of energy to keep the vehicle moving regardless of the engine setup.

[Mark]

I actually think cylinder deactivation makes good sense in having the displacement available, but only using what you need situationaly. I was surprised to learn GM didn't invent it, and it dates back as far as1905.

Total agreement with you on start/stop tech, though. That is an obtrusive tech for trying to meet overly stringent CAFE requirements

I have a number of relatives that drive larger GM vehicles, & cylinder deactivation has caused engine failure for a few. You have hot active cylinders running next to cooler deactivated cylinders and that just causes havoc within. In theory it sounds great. If it means early engine failure, that sucks!