Road trippin in the CRD

Sir Sam · **Posted:** Tue Jun 01, 2010 10:38 pm

dieseldoesit wrote:

Sir Sam wrote:

Yes.

Just because its at a higher RPM doesn't mean its burning more fuel.

It's very easy to rev the engine at idle, not easy to rev the engine when in drive(IE load attached).

Don't you have your own thread?? :goink:

I do, and if I was updating my mileage on my trip I would post it there.

mustang_gt_350 · **Joined:** Tue Jun 01, 2010 8:47 am **Posts:** 191

To comment on the High Revs while in neutral. My 98 mustang v6 auto will do the exact same thing. It's like as if its keeping the RPMs matching what it would be if it was in that gear.

As for putting it in neutral to save fuel while coasting, that i'm not sure about.

My powerstroke will shut off the injectors when the peddle is let off when you are coasting. You can hear them shut off and it changes with how fast you are going and what gear it is in as to how much peddle it takes to get the firing again.And i have heard that the VW tdi's also do this. So I'm wondering if the CRD's also do it? The only benefit i could see in doing the nuetral coast is if it was a very slight grade and the compression resistance was slowing the jeep down and putting it in N would keep that from happening, i just don't like the idea of being in N while going 50mph.

Also to the OP thats some great MPG

geordi · **Posted:** Wed Jun 02, 2010 1:46 am

mustang_gt_350 wrote:

i just don't like the idea of being in N while going 50mph.

Genuinely curious here - Why not? The engine is still running, all the accessories and safety systems are still running... You just aren't dragging down the speed of the vehicle with the weight of the motor and you have removed the loading from both the transmission and engine so they are equally getting lubed in an "idle" kind of load situation. Yea, the transmission is rotating faster, but it also is not generating any heat when receiving rotational force from the axle, b/c it is doing no work. So the fluid temps will drop like a rock.

mustang_gt_350 · **Joined:** Tue Jun 01, 2010 8:47 am **Posts:** 191

geordi wrote:

mustang_gt_350 wrote:

i just don't like the idea of being in N while going 50mph.

Genuinely curious here - Why not? The engine is still running, all the accessories and safety systems are still running... You just aren't dragging down the speed of the vehicle with the weight of the motor and you have removed the loading from both the transmission and engine so they are equally getting lubed in an "idle" kind of load situation. Yea, the transmission is rotating faster, but it also is not generating any heat when receiving rotational force from the axle, b/c it is doing no work. So the fluid temps will drop like a rock.

Just to start off i wasn't trying to be a smart booty when i said what you quoted and i apologize if it came off that way.

As long as the trans pump is still pumping while in N it won't hurt anything. I'm just kinda nervous when it comes to taking chances with AUTO's. That is the one thing i have never dug into when it comes to cars. Now i will have too when the time comes with my truck and i blow it out at the track. I guess its just the old school part of me where I have always been told its not a good idea to do.

You could have a few sides on this idea. 1. The money saved in fuel might go back in brake pad replacement and could even out. 2. If the hill is steep enough by letting it in gear you are burning no fuel by coasting as most cars/trucks shut off the injectors inlcuding gas cars/trucks while in a coasting state. I would guess that either way if you did test this out over a few tanks of fuel it would probably be insignificant to even be able to tell if it was just standard deviation in testing. This being said i have never driven a CRD. I Joined just a few days ago to do some research on one as i have always been interested in them and i'm going to look at one/test drive it tomorrow. SO i have no idea really how much drag being in gear creates vs in neutral.

danoid · **Posted:** Wed Jun 02, 2010 12:22 pm

Many gasser powertrains will continue to attempt to keep positive torque on the driveline with zero pedal input while coasting at high speeds. This is done to reduce clunks and bumps and keep the exhaust airflow at the stoichiometric air:gas ratio to keep the catalytic converters happy.

A diesel, however, usually does not need to keep anything at stoich, it is a lean burn (less than the stoichiometric air:fuel ratio) by definition. They therefore usually completely turn off the injectors if they are not needed. One common driving circumstance where no torque is needed is when the driver lets off the pedal and the car is coasting, and the transmission is holding the engine rpm above the low idle limit.

At this point the vehicle is moving forward and using absolutely no fuel. INFINITE MPG. If, however, you shift to neutral, then the engine rpm drops to idle and the engine controller has to add fuel to avoid stalling the engine. Less than infinite mpg.

Please don't consider turning off the engine while coasting either. The transmission lubrication pump is driven directly by the engine crankshaft. No crankshaft rpm, no lubrication in transmission, sooner or later a burnt transmission. This usually happens when a vehicle is being towed, ask any motorhome RV'er about flat towing, they will know.

Keep it in gear as long as the torque converter is locked up. Yes the coasting drag is higher than shifting into neutral. That's because you are using vehicle momentum instead of fuel to keep the engine rotating.

geordi · **Posted:** Wed Jun 02, 2010 12:42 pm

Ah, well welcome to the board. As a Ford guy, have you heard about FordVsChevy.com? One of the best forums on the intertubez.

Anyway, if your CRD (I'm being hopeful, you should buy it if it is a good deal - They rock) SO.... If YOUR CRD is still in stock form, then there is a HUGE difference in the coasting performance between in-gear and neutral.

The reasons for this are mostly in the exhaust system and the electronic tune however. The stock system has a VERY restrictive exhaust system (whether or not you choose to deal with the cat is a separate issue, but that contributes a fair amount of back pressure) and the stock muffler is ridiculously heavy and also restrictive. It needs to be the first thing to go - Get a Flowmaster for about $80 that weighs only about 20 lbs and will do its job without causing any backpressure. Second, there is a restrictive internal flange after the cat that takes the 2.5" exhaust down to about 2"... Cut that crap off of there.

That will instantly make the CRD feel like it will coast for miles in gear. What you basically have is a factory-installed Jake Brake that is always active. Yuck. (Although I have noodled with the thought of installing my own Jake on my CRD...)

Electronically - The only real fix is from Green Diesel Engineering. That is the best $500 you will EVER SPEND and it will pay itself back many times over. I don't know if I believe that the engine completely shuts off the injectors... The Vulcan in me says that isn't logical. The rotating mass is still developing compression, which is acting to retard the forward speed. A Jake Brake does the same thing but at a much larger level, not allowing the cylinders to exhaust that pressure anywhere... So they HAVE to reduce speed, which then drags down the vehicle speed. Our engines develop something north of 15:1 compression (Can't recall exactly) but the TDI is 19:1.

That is an impressive amount of air movement to do without fuel. Perhaps it is only injecting "just enough" which seems like the injectors are off? This is where I really am not sure what is going on internally. I know I can measure the fuel usage at idle, and whether the wheels are spinning in neutral or not, if the engine is running, so is the transmission pump. So lubrication is happening. At the same time, idle consumption on our engine is only one quart per HOUR of fuel. (confirmed b/c I use my CRD as a portable hotel on long trips) I can live with it using that tiny amount while floating downhill, over an unknown-but-infinitesimally-smaller savings from being in gear. Whatever floats your boat. To me, it just feels like it will coast longer and easier when it isn't in gear.

mustang_gt_350 · **Joined:** Tue Jun 01, 2010 8:47 am **Posts:** 191

geordi wrote:

Ah, well welcome to the board. As a Ford guy, have you heard about FordVsChevy.com? One of the best forums on the intertubez.

Anyway, if your CRD (I'm being hopeful, you should buy it if it is a good deal - They rock) SO.... If YOUR CRD is still in stock form, then there is a HUGE difference in the coasting performance between in-gear and neutral.

The reasons for this are mostly in the exhaust system and the electronic tune however. The stock system has a VERY restrictive exhaust system (whether or not you choose to deal with the cat is a separate issue, but that contributes a fair amount of back pressure) and the stock muffler is ridiculously heavy and also restrictive. It needs to be the first thing to go - Get a Flowmaster for about $80 that weighs only about 20 lbs and will do its job without causing any backpressure. Second, there is a restrictive internal flange after the cat that takes the 2.5" exhaust down to about 2"... Cut that crap off of there.

That will instantly make the CRD feel like it will coast for miles in gear. What you basically have is a factory-installed Jake Brake that is always active. Yuck. (Although I have noodled with the thought of installing my own Jake on my CRD...)

Electronically - The only real fix is from Green Diesel Engineering. That is the best $500 you will EVER SPEND and it will pay itself back many times over. I don't know if I believe that the engine completely shuts off the injectors... The Vulcan in me says that isn't logical. The rotating mass is still developing compression, which is acting to retard the forward speed. A Jake Brake does the same thing but at a much larger level, not allowing the cylinders to exhaust that pressure anywhere... So they HAVE to reduce speed, which then drags down the vehicle speed. Our engines develop something north of 15:1 compression (Can't recall exactly) but the TDI is 19:1.

That is an impressive amount of air movement to do without fuel. Perhaps it is only injecting "just enough" which seems like the injectors are off? This is where I really am not sure what is going on internally. I know I can measure the fuel usage at idle, and whether the wheels are spinning in neutral or not, if the engine is running, so is the transmission pump. So lubrication is happening. At the same time, idle consumption on our engine is only one quart per HOUR of fuel. (confirmed b/c I use my CRD as a portable hotel on long trips) I can live with it using that tiny amount while floating downhill, over an unknown-but-infinitesimally-smaller savings from being in gear. Whatever floats your boat. To me, it just feels like it will coast longer and easier when it isn't in gear.

Nice post. I'm more of a straight pipe or glassplack type muffler guy. The less baffles in the way the better, especially for a turbo. So that would be the first thing i would probably do along with a different intake.

Wow a quart of fuel at idle is very meager. Thats some good info to know, i bet these take FOREVER to warm at idle. Do they have any built in programming in the ECU that auto increases the idle RPM at idle when its cold?

Also the exhaust brake would add some cool factor. You should go for it

Has anyone ever hooked up a scope while driving to monitor Injector pulse width to see if they do indeed shut them down completely when coasting. Kinda like this vid of some of my tinkering a while back. http://www.youtube.com/watch?v=lWU2R1IyouQ

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

The CRD will completely shut off the fuel injection if coasting with the engine rpm above roughly 1200. Danoid's information is accurate. Below this rpm the fuel starts injecting as the low idle governor turns on. It generally injects 8-10 mm^3 of fuel at idle (760rpm) in neutral and around 20 mm^3 in drive per cylinder. Add 3-5mm^3 of fuel injected at idle if the AC is on. This info comes from a fully warmed up engine.

Knowing if it is better to let the vehicle coast in neutral or stay locked up in gear depends on several factors including speed, load, hills, gear, etc. Not to mention it is difficult to complete/analyze A to B testing that shows any significant difference between fuel used and distance covered since the timeframe is usually short.

mustang_gt_350 · **Joined:** Tue Jun 01, 2010 8:47 am **Posts:** 191

GreenDieselEngineering wrote:

The CRD will completely shut off the fuel injection if coasting with the engine rpm above roughly 1200. Danoid's information is accurate. Below this rpm the fuel starts injecting as the low idle governor turns on. It generally injects 8-10 mm^3 of fuel at idle (760rpm) in neutral and around 20 mm^3 in drive per cylinder. Add 3-5mm^3 of fuel injected at idle if the AC is on. This info comes from a fully warmed up engine.

Knowing if it is better to let the vehicle coast in neutral or stay locked up in gear depends on several factors including speed, load, hills, gear, etc. Not to mention it is difficult to complete/analyze A to B testing that shows any significant difference between fuel used and distance covered since the timeframe is usually short.

Nice data.

If/when i do get a CRD I will be coming your way GDE.

So that means at idle injecting 10mm^3 is .01cc of fuel per injection

So 760 rpm is 1520 injection events per min
91200 per hour
=912cc per hour which = 30.84 ounces per hour of idle. So that comment about the quart per hour at idle is very very close.

boilermaker2 · **Posted:** Thu Jun 03, 2010 11:09 pm

Interesting conversation guys. To see the difference in a stock unit is easy in flatlands. Got to a set speed on a route you travel each day and coast from a given telephone pole to full stop. Then flip it into neutral at the same post.
Neutral beats it hands down.

Road trippin in the CRD

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