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Unread 08-15-2010, 07:22 PM   #46
Sweeney
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Quote:
Originally Posted by nitecop View Post
You will use more fuel if you shift to neutral and let the engine idle.
Most ALL EFI engines Shut off fuel completly IF the vehicle is above 20 mph, throttle is closed completly and the engine is above 1000 rpm. So as you can see you will save the most fuel if you just let off throttle completly going downhill.
You missed the point. The coasting is done to prevent a scenario where you are in the highest gear traveling down hill yet need to open the throttle to prevent compression braking so to maintain speed. The engine is running at 2000rpm or so burning more fuel than if it were just idling.

I have observed the injector duty cycle roughly double that of idling in these situations. My average mpg for the days I observed this (during my commute) was 1.7 mpg higher when I allow the Jeep to coast where appropriate. This was a sample size of 20 days, 10 coasting, 10 leaving it in gear, alternating days.

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Unread 08-15-2010, 08:41 PM   #47
nitecop
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Quote:
Originally Posted by Knuckelhead View Post
Do you have an accredited source to back that up for the 4.0L, TJ engine/PCM function?...
Well all I can say about my TJ is that I feel it kick idle fuel back in when caosting across the 1000 RPM threshold.

I worked at Crane Cams 20 years ago as a techical consultant when we developed the Interceptor piggyback ECM for Ford 5.0 stangs (My 88 GT was the main test car) I learned quite a bit about EFI operation in Ford, GM and most others.

I can also say this about my TJ while on vacation last year in colorado I was coasting for miles downhill in gear when I noticed my temp gauge had dropped to allmost 160. In other words the thermostate had closed.
If the vehicle was getting idle fuel it would have stayed at the normal operating temp.
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Unread 08-15-2010, 09:30 PM   #48
PA_LJ
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This thread seems silly. I skimmed through the last two pages.

I used to ride the clutch and coast all over the place when I learned how to drive a manual transmission. (93 Ford Escort)

When transitioning into my old YJ i started to focus on downshifting through gears and letting the engine do the work. With 33's and a 4 cyl you need all the momentum you can get to keep rolling, no sense in taking all the power away by laying the clutch down and coasting.

Now I consistently use engine braking in my LJ.

I can tell a difference between my driving style and my wife who still coasts with the clutch in. I find myself consistently in the proper gear where she struggles to find the right one. I also find that I can time traffic lights with ease.
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Unread 08-16-2010, 12:50 AM   #49
bruteboy
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Quote:
Originally Posted by wushaw View Post
What is likely to hurt a Eaton clutch coasting with tranny in neutral?, the engine will be at idle.
I said clutches can be damaged from "coasting" under certain conditions.if you are coasting in "neutral" with the clutch engaged it wont be damaged.
if you are coasting with the clutch disengaged and the transmission in a low enough gear,the clutch disc can be overdriven and may cause the disc to be damaged.
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Unread 08-16-2010, 06:50 AM   #50
Sweeney
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Quote:
Originally Posted by PA_LJ View Post
With 33's and a 4 cyl you need all the momentum you can get to keep rolling, no sense in taking all the power away by laying the clutch down and coasting.
This makes zero sense relative to this thread. The thread is not about compression braking. It's not about braking at all. It's about letting the Jeep roll freely to avoid the need to open the throttle while in gear to maintain speed while descending a slope.

Here's a scenario; You wish to maintain 50mph while descending a slope. With the clutch engaged and the transmission in its highest gear, compression braking (throttle closed) only allows the Jeep to reach 35mph. To reach 50mph you need to open the throttle essentially revving the engine freely (no load involved except internal engine load). The ECU is now no longer in a 'decell' or fuel cut off mode. With the transmission in neutral and clutch engaged (unless you like killing your throwout bearing) the Jeep will freely roll at the desired 50mph. You will burn less fuel.

Think of it this way; you allow the engine to idle for 15 minutes or you hold the throttle open at 2000rpm 15 minutes... which burns more fuel?
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Unread 08-16-2010, 06:53 AM   #51
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Quote:
Originally Posted by bruteboy View Post
I said clutches can be damaged from "coasting" under certain conditions.if you are coasting in "neutral" with the clutch engaged it wont be damaged.
if you are coasting with the clutch disengaged and the transmission in a low enough gear,the clutch disc can be overdriven and may cause the disc to be damaged.
If you coast in a low gear while holding the clutch disengaged you deserve to have the clutch fragment, severing both feet and suffer a prolonged, painfully slow bleed out. It's how Darwin would want it.
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Unread 08-16-2010, 10:02 AM   #52
PA_LJ
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Quote:
Originally Posted by Sweeney View Post
This makes zero sense relative to this thread. The thread is not about compression braking. It's not about braking at all. It's about letting the Jeep roll freely to avoid the need to open the throttle while in gear to maintain speed while descending a slope.

Here's a scenario; You wish to maintain 50mph while descending a slope. With the clutch engaged and the transmission in its highest gear, compression braking (throttle closed) only allows the Jeep to reach 35mph. To reach 50mph you need to open the throttle essentially revving the engine freely (no load involved except internal engine load). The ECU is now no longer in a 'decell' or fuel cut off mode. With the transmission in neutral and clutch engaged (unless you like killing your throwout bearing) the Jeep will freely roll at the desired 50mph. You will burn less fuel.

Think of it this way; you allow the engine to idle for 15 minutes or you hold the throttle open at 2000rpm 15 minutes... which burns more fuel?
I still like compression braking.
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Unread 08-16-2010, 10:36 AM   #53
Sweeney
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Quote:
Originally Posted by PA_LJ View Post
I still like compression braking.
I like compression braking too and use it all the time... when I want to brake.
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Unread 08-16-2010, 12:44 PM   #54
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I can't believe there is 53 (54) reply's to this. x100 no damage to engine to be out of gear while moving. I have never "hunted" for a gear. I look forward to reading the other 2 pages when I get home from work LOL
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Unread 08-16-2010, 12:58 PM   #55
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Quote:
Originally Posted by bruteboy View Post
if you are coasting with the clutch disengaged and the transmission in a low enough gear,the clutch disc can be overdriven and may cause the disc to be damaged.
You wouldn't be coasting anymore and yes that's a good way to destroy any clutch.
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Unread 08-16-2010, 10:10 PM   #56
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You can teach some one to drive stick, but you can't tell some one how to drive stick.

Quote:
Originally Posted by BlueFlame View Post
Just like with any manual trans shifting/operation question - it's situation dependant...

... coasting in gear using engine braking is good when you're needing to slow down soon ...
Quote:
Originally Posted by BlueFlame View Post
coasting either out of gear or with clutch depressed is clearly better when you Don't need to slow down...
.
Never hold the clutch in longer then to shift.
If you press the clutch to slam on the brakes you can usually take it out gear.



And again, to stay on topic ...
Coasting in neutral with a manual transmission will not harm your engine
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Unread 08-17-2010, 12:12 AM   #57
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Quote:
Originally Posted by nitecop View Post
Well all I can say about my TJ is that I feel it kick idle fuel back in when caosting across the 1000 RPM threshold.

I worked at Crane Cams 20 years ago as a techical consultant when we developed the Interceptor piggyback ECM for Ford 5.0 stangs (My 88 GT was the main test car) I learned quite a bit about EFI operation in Ford, GM and most others.

I can also say this about my TJ while on vacation last year in colorado I was coasting for miles downhill in gear when I noticed my temp gauge had dropped to allmost 160. In other words the thermostate had closed.
If the vehicle was getting idle fuel it would have stayed at the normal operating temp.
Care to clarify this part?

So you were coasting in gear down hill and your jeep got cooler?
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Unread 08-17-2010, 12:34 AM   #58
phillies4752
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I coast down hills with my transition in neutral....I hold the clutch in (while in neutral) .... is that bad????
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Unread 08-17-2010, 01:20 AM   #59
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Quote:
Originally Posted by OlllllllllO View Post
I coast down hills with my transition in neutral....I hold the clutch in (while in neutral) .... is that bad????
Yea, your putting unnecessary wear on your throw out bearing.
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Unread 08-17-2010, 06:51 AM   #60
mikevsgeek
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Compression braking is supposed to be used to help maintain vehicle speed down long grades vs constantly applying the brakes and possibility getting into a overheating brake situation.

By coasting down a hill in neutral, you risk putting your jeep in an over speed condition. Lets say you are doing 70mph down hill, which for me with the 4.0 w/ NV3550, 4:10s and 33s, is about 2000 rpms. All of my engine accessories are running at the correct speed to maintain the proper engine environment (water pump, oil pump) and the input shaft on my transmission is also spinning at the correct rate so that proper lubrication can occur. Now lets say I coast down the hill in neutral, my engine is idling at 800rpm give or take so now my engine may not be getting the correct cooling or oil lubrication that it needs and my input shaft into the transmission is no longer spinning meaning that my transmission might not be getting the lubrication that it needs. So then lets say I coasted down the hill in neutral and towards the bottom of the hill I'm doing 75mph and I put it in 5th and let of the clutch, I'm going to risk the possibility of put a shock load on my engine, transmission and drive line components.

The rule of thumb for going down hills is that you should be in the same gear that you would need to be to go up the hill.

And if your so worried about your MPG, you probably shouldn't have bought a jeep in the first place
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better economy , better mileage , coasting , driving , in gear , manual , miles per gallon , mpg , neutral

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