Engine/Transmission (1998.5 - 2002) 3 cylinder cold idle

[Smokewagon359]

Someone tell me what is the advantage of the 3 cylinder cold idle? If I'm not mistaken, the smarty provides this feature. I may be wrong. My buddy pulled up behind me at the pump the other day, and his truck was hitting on three. I almost moved out of his way, because I thought something was wrong with it. I started talking to him, and I didn't even want to mention it, but then he told me it was supposed to do that when it was cold. When he left the station and got on it, it sounded almost as good as mine :-laf . Somebody tell me something, cause I'm curious now.

 

[ToolManTimTaylor]

3 cyl should not have been active if he pulled up behind you. It will defeat once the brake pedal is depressed , Gear selector moved , or if engine is above 16*F

 

[Smokewagon359]

3 cyl should not have been active if he pulled up behind you. It will defeat once the brake pedal is depressed , Gear selector moved , or if engine is above 16*F

I'm not sure what was going on. Talking to him made me think he really didn't either.

 

[Smokewagon359]

It really wasn't that cold either. All I saw was an EZ under the hood and he had changed to another injector pump, but couldn't even remember what kind it was.

 

[ToolManTimTaylor]

If it was a "Hot rod" style VP44 then I am willing to bet you heard a "Lopey Idle" that some trucks exhibit especially with larger lines and crossover tubes.

 

[JCyrbok]

The advantage is that running on three cylinders while idling when cold puts a load on the engine (moving three dead cylinders) and thus warms up/keeps engine warm to prevent fuel washdown in the cylinder and sticking of valves. Plus is sounds REALLY COOL!!!!LOL



As stated above just touching the brake would have cut out the high idle/3 cylinder cut out, so that you can not drive down the road in that condition. Mine will kick high idle back in if I drive down the road to get fuel and it is really cold out, but anything more that a couple of mile gets "enough" heat into the engine that it meets the criteria for it not to kick in.



J-

 

[Devan Manis]

Mine did the 3 cylinder idle a couple of weeks ago because I forgot to plug it in, and I started it up and went inside. Then i heard it and thought something was wrong, so i went out and checked all of my gauges and all was well, then i looked at the temp gauge in our tdi and it said 8 degrees and I remembered that we had the three cylinder idle on it.

 

[cojhl2]

The advantage is that running on three cylinders while idling when cold puts a load on the engine (moving three dead cylinders)

If this is true and I assume it is,, then why is it more efficient to shut down some cylinders (on engines that do so) while cruising down the road.



This has always bothered me.



I've posted this question before but have not received an answer. .

 

[SnoKing]

If this is true and I assume it is,, then why is it more efficient to shut down some cylinders (on engines that do so) while cruising down the road.



This has always bothered me.



I've posted this question before but have not received an answer. .

Displacement of demand works differently. It holds a valve open, so the cylinder does not add a load. SNOKING

 

[cojhl2]

Displacement of demand works differently. It holds a valve open, so the cylinder does not add a load. SNOKING

Okay, that makes sense. I did not realize the valve train was involved. That must mean the work done to overcome the throttle vacum on a gas engine is considerable.



On a non throttled engine like a diesel since the work taken to compress is returned(theoretically) it would not work during cruise I guess.



It still seems though to be confusing on this startup however,, It takes a given amount of energy to rotate the engine regardless how many cylinders fire. So the heat produced and wasted(to warm the engine) is the same?



Must be because when 3 cyls fire instead of 6 the temp is higher??.



My brain is busted I gotta go lest I ramble some more!!!!!



edit: changed wording

 

[isb360]

Another thing that happens during 3-cylinder operation is that in order to maintain idle speed, extra fuel is being squirted into the three live cylinders and between extra fuel and extra load, it drives EGT's up which help warm the engine.



On a cold morning with all 6 cylinders firing, my truck will idle (when not warmed up) at under 200F EGT (about 190-ish... ), but when it cuts to three, the EGT's climb and steady out at 500F. I can't make it hit 500F on 6-cylinders regardless of the RPM, so from the standpoint of trying to generate heat and get it into the block (and coolant for you!), it is very effective.



On another note: I didn't realize the DoD systems manipulated valves, I thought they purely shut down injectors. Interesting. I didn't think the 5. 7Hemi had any kind of intelligent cam system (yet!)... . although one is coming with variable valve timing.



Tim

 

[cojhl2]

On another note: I didn't realize the DoD systems manipulated valves, I thought they purely shut down injectors. Interesting. I didn't think the 5. 7Hemi had any kind of intelligent cam system (yet!)... . although one is coming with variable valve timing.



Tim

Whoops,, I did not mean to imply that I thought valves were manipulated on a diesel.



I am discussing two different scenerios here. 1) Cold start 3 cyl, 2) Crusising with cylinders shut down like Cadillac used to do. From what I get out of this thread,, the Hemi does also??



I was using one situation to understand the other.



On a diesel, a "Jake" would do the valve manipulation if you chose to do so. But you obviously would not do this to cruise.



I have seen mechanics warm an engine up by taking it to 2000, let off the pedal and force the Jake to shut the engine down to almost idle then pedal down to take the engine back to 2000. . Do this repeatedly and the engine gets to operating temp.

 

[johncameron]

I just recorded my truck going through it's normal cycle from start to 3-cyl high idle. It was recorded with a Shure KSM27 micophone through a ART tube MP preamp. No processing was done.



Have a listed to the racket !! 3. 5MEGS



http://www.wikiupload.com/download_page.php?id=58360



John