3 cylinder idle

[Crunch]

Can anyone explain what this is, what it does and how it works? It sounds cheesy to me, but what I've never heard of it before I bought my truck.

 

[Scrappy]

3 cyl idle

I have been told that the 3rd gens. have a high idle but no 3 cyl. mode.

 

[Peter Campbell]

With electronic injectors the ECM can just "turn off" some cylinders. If the engine is very cold and you have incomplete combustion then the unburnt fuel will tend to wash the lubricant off the cylinder walls- a bad thing. Given that it takes a certain amount of fuel to turn the engine at idle- if you have that fuel delivered to three cylinders instead of 6 then the fuel delivered per active cylinder is higher. Higer combustion temps, higher EGT for those cylinders. warmer piston in those cylinders. The idle cylinders are doing nothing but pumping air. So it is to save wear and tear on the engines- and emissions. Emmissions is what made the manufacturers finally put the feature on. Otherwise they would just say no extended idling in the owners manual and be done with it.

 

[Scrappy]

3cyl.

Diesels only warm up under load, by turning off 3 cylinders, the remaining 3 are "loaded" by pumping air in the other three so the truck will warm up. only enough fuel is given to each cylinder to maintain the engine's rpms under "load".

 

[ImagesThatSing]

So does the 3rd Generation engine have this feature or no?



Seems to be a difference of opinion maybe.

 

[gsbrockman]

I don't believe the 3rd Generation trucks have the 3 cylinder mode. I have, however, experienced the high idle mode first hand on my truck. After about two minutes of idling (and heaters cycling on and off) the engine automatically increases idle to 1,000 rpm's or so. Can't tell you how long it lasted, as I went back in to finish breakfast the one time I've experienced it. The outside temperature was 31* F according to the overhead console. The truck was cranking out decent heat for the time it had been running... . much more heat than my 2000 Dodge 2500 CTD.

Greg

 

[Rosco]

One more thing to note about the high idle feature for recent 3rd gen graduates. Under certain conditions (like very cold temperatures) the truck will skip the two minute rule and jump right to the high idle at start up so don't be alarmed.

 

[TBrennan]

Definately will jump to high idle on start up, mine did this morning and it was about 30 deg. F.

 

[DBVZ]

It seems to me any fuel injection engine will have an optimum fuel mixture and fuel volumn / cylinder when running. The ECM (or equivalent) should be able to turn them on and off as needed depending on power needs. For our trucks, perhaps 6 for pulling, 4 for cruising, and just 2 for a long downgrade or idle. I sent a suggestion like this in to DC some time ago. No royalties yet. It could be done on a cycle basis, going more turns between power strokes. With optimum volumn and mixture, it ought to improve fuel economy as well as emission numbers.

 

[DPKetchum]

Had high idle this A. M. Overhead said about 40 degrees. dropped to about 32/33 degrees last night.

 

[gsbrockman]

Originally posted by DBVZ

It seems to me any fuel injection engine will have an optimum fuel mixture and fuel volumn / cylinder when running. The ECM (or equivalent) should be able to turn them on and off as needed depending on power needs. For our trucks, perhaps 6 for pulling, 4 for cruising, and just 2 for a long downgrade or idle. I sent a suggestion like this in to DC some time ago. No royalties yet. It could be done on a cycle basis, going more turns between power strokes. With optimum volumn and mixture, it ought to improve fuel economy as well as emission numbers.

I think GM tried this once on a Cadillac and failed miserably.

Greg

 

[E7mack96]

Yes they did - It was something like the 4-6-8.



Big bomb (not in the good sense)

 

[DPKetchum]

Actually it worked preety good. Was only one year. It didn't give really any trouble and they got great fuel mileage. I've driven them and handled repairs on 4/6/8 caddys. I thought they would be a pain to handle/work on but were ok. Techs thought they were kinda cool. Not hard to trouble shoot or make run good.

 

[Blakers]

Originally posted by DBVZ

It seems to me any fuel injection engine will have an optimum fuel mixture and fuel volumn / cylinder when running. The ECM (or equivalent) should be able to turn them on and off as needed depending on power needs. For our trucks, perhaps 6 for pulling, 4 for cruising, and just 2 for a long downgrade or idle. I sent a suggestion like this in to DC some time ago. No royalties yet. It could be done on a cycle basis, going more turns between power strokes. With optimum volumn and mixture, it ought to improve fuel economy as well as emission numbers.

Kinda like a hit and miss engine... Just fires when it needs to. Late 1800's technology, only with a computer!