Curiousity Question (Chris)

I have heard multiple times that the injectors shut off when no throttle is applied but the truck is left in gear, until the engine winds down to about 1k rpms.

My question is how can the rpms remain high with no fuel being delivered?

This question is not about driving habits, just my curiosity to how the engine works. Thanks!

 

I think it has to do wit the trucks momentum. It keeps the engine spinning at speed.

 

Ok, so the engine is still pumping due to the momentum of the truck? I guess I don't understand how the truck can continue running with no fuel, much less at higher RPMs.

I guess this is how we start up old tractors when they stall.

 

Gotcha, so when I am on a moderate hill where I could either coast in neutral and maintain speed, or coast in gear and maintain speed, I would rather leave it in gear. Correct?

I don't have the pre-reqs done to take internal combustion engines so thanks for the lessons!

 

Imagine lifting the truck off of the ground with all four wheels off of the ground with a car lift. Then imagine grabbing the rear wheels at the same time and spinning them forward real fast with the truck in gear. If you did the same thing with the truck in N gear, than the engine would not spin and only the trans would spin and the rear diff,.

When it's in gear or D gear (drive gear), than it will grab onto the engine and spin or turn over the engine.

 

Leave it in gear. If you put it in N too much, you'll burn the tranny fluid out cause it's pumped to the cooling via the truck being in gear and moving.

Or something to that effect.

Either way moving + N too much = truck

 

Ok thanks for the explanations!

 

Wait... the injectors shut off? That actually might explain why there's a lag sometimes in kicking in... almost like it was dropping out of OD but it's not. Now how to shut that off :/

 

Got it! So it is (simplified) much like when we hook one tractor up to a dead one and get the engine to start by towing it and poping the clutch?

Alright. I asked this question with my manual tranny in mind but that is good info for the others reading this!

 

My bad. I looked and saw the 4x4 and the 4 cyl but totally missed the manual.

My bad.

 

No problem at all, I love learning about anything to do with our trucks, even if it doesn't pertain to mine.

SJ-do you think cruising in neutral has the same affects on the manual tranny oil? The reason I ask is on interstates, no matter the grade around here, if you coast in gear, you will lose speed. Sometime on interstates (especially leaving my school in the mountains) I coast in neutral since I cant afford to lose my momentum in gear. Sometime I can get up to 3 miles coasting in neutral with the engine at idle, as opposed to 5th gear around 2300 rpms

 

i've never heard of this before.i'm realy curious of how that system works or why they did it.if anyone has a link of where this is exsplained let me know.this is something i would like to know more about.

 

Looks like we are in the same boat. I understand much better now after the responses in this thread. Basically (in engineering terms) the work done by the spinning tires travels through the drive train and provides enough work on the engine that it can continue to run without the added energy of fuel combusting

 

It kinda sounds as if you already knew all of this lol.

 

Nope I just never put two and two together until you all provided enough of an explanation to make it click in my head!