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Author Topic: MPG and Jakes  (Read 3607 times)
Nick Badame Refrig/ACC
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« on: December 05, 2007, 10:58:19 AM »

Hi Guy's,

This morning I traveled 10 miles down the road to fuel up for an excursion to Cabella'a tomorrow with some friends.

After filling 88 gallons into the tank, "at $334.9 gal" I did my milage calculations and for the past 3/4 months I have

dropped in MPG to 5.8 to 6.2. I was averageing 6.5 to 7.5 depending on weather I was pulling the Yukon or not.

Question.... Does my newly installed Jake's effect my fuel milage?

I do notice that when the jakes are inguaged, there will be a bit of unburned fuel comming from the exhaust that

I can only see at night time when there are headlights shinning from behind.

Thanks in advance
Nick-
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« Reply #1 on: December 05, 2007, 12:05:38 PM »

Nick - If you leave your jakes on all the time your not going to get any coast out of your D-train - I only use mine on grades - FWIW
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« Reply #2 on: December 05, 2007, 12:22:51 PM »

Nick - If you leave your jakes on all the time your not going to get any coast out of your D-train - I only use mine on grades - FWIW

I agree with Niles. If you are leaving your Jake on all the time, it is like putting on your brakes every time you take your foot off the accelerator.

Richard
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« Reply #3 on: December 05, 2007, 12:53:53 PM »

PLUS, as you know, there is a huge difference in "around town and over the road" >>>Dan
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« Reply #4 on: December 05, 2007, 01:07:33 PM »

I do notice that when the jakes are inguaged, there will be a bit of unburned fuel comming from the exhaust that I can only see at night time when there are headlights shinning from behind.
Thanks in advance
Nick-

Nick, it is my opinion that there will always be a small amount of unburned fuel. There is always enough fuel from the injectors to maintain engine idle speed even with the Jakes engaged. Since the Jakes are opening the exhaust valves, this fuel is not burned and would appear as unburned fuel in your exhaust.

This is my opinion until someone comes up with a better answer or explains how the fuel could be turned completely off.

Richard
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« Reply #5 on: December 05, 2007, 01:13:16 PM »

Also what you may be seeing in the exhaust at night with the Jake working may be engine oil being sucked past either the rings or valve guide seals.  This can happen with mills in excellent condition.  The only other thing I can think of and it doesn't make any sense is that your fuel system is not completely shutting off when the Jake is applied and you are seeing unburned fuel like you said.

Yeah, the Jake is soosss neat that we tend to use it like service brakes all the time if it is left "on" all the time.  Saves your brakes, but the Jake can change our driving habits to the point that we do loose energy of the coach ordinarly coasting but instead being greatly slowed quickly by the use of the Jake.  Sorry for my lousy riting style today....I need more red wine.  He he he.  Smiley Smiley Smiley
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Nick Badame Refrig/ACC
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« Reply #6 on: December 05, 2007, 02:40:06 PM »

Thanks Guy's

I do have a bad habbit of leaving the jakes on....  I will work on that..

One thing I noticed, in cold weather the jakes work exceptionally well. I guess it's the thicker oil.

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« Reply #7 on: December 05, 2007, 02:50:57 PM »

Thanks Guy's

I do have a bad habbit of leaving the jakes on....  I will work on that..

One thing I noticed, in cold weather the jakes work exceptionally well. I guess it's the thicker oil.

Nick-

I think it has something to do with the exhaust valve clearances that were set during installation. I found that when the engine was cold the Jakes worked significantly better than when the engine was up to temperature. I suspect it has something to do with the clearances increasing as the engine warms up. I went in and changed my valve clearance from .059 to .055 and it really made a great improvement in the operation when the engine gets up to operating temperature.

Richard
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« Reply #8 on: December 05, 2007, 05:34:01 PM »

Richard, when the engine is turning quite a bit faster than the governor is calling for, the fuel should turn off completely at avery injector. There should be no fuel injected to maintain idle until the engine speed drops down to something near the governor setting.

I have seen the haze or small amount of smoke that you refer to and I have wondered about it, too. The only thing that I could think of is that there might be a small amount of lube oil mist coming out the exhaust.

I could see that this might happen if the jake completely relieved the compression while the piston was up and the valves closed before it went down too far. That would lead to a vacuum forming over the piston before it uncovered the intake ports.

I don't see how a vacuum might form around the valve stems, however.

For what it's worth.

Tom Caffrey
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« Reply #9 on: December 05, 2007, 07:06:28 PM »

Richard, when the engine is turning quite a bit faster than the governor is calling for, the fuel should turn off completely at avery injector. There should be no fuel injected to maintain idle until the engine speed drops down to something near the governor setting.

I have seen the haze or small amount of smoke that you refer to and I have wondered about it, too. The only thing that I could think of is that there might be a small amount of lube oil mist coming out the exhaust.

I could see that this might happen if the jake completely relieved the compression while the piston was up and the valves closed before it went down too far. That would lead to a vacuum forming over the piston before it uncovered the intake ports.

I don't see how a vacuum might form around the valve stems, however.

For what it's worth.

Tom Caffrey

You may be entirely right, but I was under the impression that the governor could not turn the fuel off entirely. It could only reduce the amount to what is required to keep the engine at idle speed.
Again, only an idea of mine.
Richard
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« Reply #10 on: December 05, 2007, 07:07:41 PM »

Nick, i suspect if you leave the jakes on and drive mostly downhill, your mileage will improve back to what it was.  you are obviously driving uphill too much.  go DOWN to the coastline and stay there.

or head down to florida at this time of year.
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« Reply #11 on: December 05, 2007, 07:11:51 PM »

Nick, i suspect if you leave the jakes on and drive mostly downhill, your mileage will improve back to what it was.  you are obviously driving uphill too much.  go DOWN to the coastline and stay there.

or head down to florida at this time of year.

Or put Great big tires on the back end of your bus and itty bitty tires on the front.

That way you'll always be going downhill!  Grin

DF
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« Reply #12 on: December 05, 2007, 07:56:52 PM »

I use the Jake intermittently, when going down grades, in any gear, and to slow at a stop light or sign.  I note that at  highway speed, black smoke is often emitted, but when in lower gears, not necessarily so.  and yes....I do think it changes fuel mileage.  This opinion after 6 years of using the coach, mostly in the western part of the US, but also a number of trips east including Nova Scotia.

But....worth EVERY penny ( dollar ?)   Wink

FWIW

RCB
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« Reply #13 on: December 05, 2007, 10:02:57 PM »

I have heard truckers say that leaving the jakes on will decrease mileage because they will often get activated when the driver only wanted to coast, but now has to use fuel to regain momentum lost. Not the most efficient way to travel and mostly due to inattention. Not the main reason, but defiantly one of the reasons, I installed a momentary-on foot switch in parallel with my Jake toggle switch. I only activate it when I need it, and Iím not fumbling for the switch all of the time.

Could what you are seeing at night be moisture condensing in the cool air? The hot compressed air, when dumped into the cold atmosphere, will have its moisture condense right? I was also under the impression that the fuel was cut off until reaching idle but I really donít know all that much about the operation of the governor.

Laryn


Photo of when I was installing the jake foot switch in the hole where the clutch used to be.
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« Reply #14 on: December 06, 2007, 02:13:18 PM »

I mentioned valve guide seals as well as the rings being a potential source of nighttime exhaust pipe smoke/hazzing during Jake operation because I was told that since the exhaust valves are only being cracked open, a situations can/does exist that lets oil weep past the seals.   Something to do with pulse cycling or the seal material memory or valve stem wear or temperature cycling or something like that for whatever it is worth.  Anyway, that is what the factory Jake Brake engineers said long ago and far away.   Smiley Smiley Smiley
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Nick Badame Refrig/ACC
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« Reply #15 on: December 06, 2007, 06:58:57 PM »

Hi Guy's,

I'm back from my day trip to Hamburg, P.A. and burned 60 gallons. I left the jakes off most of the day and when I topped off this evening

my mpg was back to 7.5... Oh, and that mist out the exhaust is not there with the jakes off. Hummmm....

Thanks for everyone's help on this!
Nick-

PS, my 4 friends left over 2 grand with mr. Cabella...  And my middle bay loaded to the hilt!  Angry
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« Reply #16 on: December 07, 2007, 05:30:37 AM »

Hi Guy's,

Oh, and that mist out the exhaust is not there with the jakes off. Hummmm....
My guess is still unburned fuel. I do not think the governor is capable of shutting the fuel off entirely. Only down to enough for idle. To shut the fuel off completely the governor must be actuated by an air cylinder to stop the engine.

Richard
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Nick Badame Refrig/ACC
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« Reply #17 on: December 07, 2007, 06:16:58 AM »

Hi Richard,

I think you are correct..

Nick-
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« Reply #18 on: December 07, 2007, 07:18:09 AM »

Nick, I added one of those plastic covers (like aircraft used to use on the landing gear switch or the rodders use on their Nitro switches) which is on the console to my left.  With the switch for the Jakes on I have a constant reminder that they're switched 'on'.

Leaving them constantly 'on' will not only take it's toll on milage but it sure is a hell raiser with the muffler too! I used to have a pretty solid muffler...now I sound like a freight train.  Shopping for a new muffler at present.

Anyone have a good aftermarket link for an MC5A muffler?

Bob
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« Reply #19 on: December 07, 2007, 10:27:28 AM »




 Bob

   I can get you a muffler like is on "Huggy"  Dallas seems to like it. He can tell when i am coming several miles away.

   Hope you and jackie are well and enjoying the warmth. Was 29 degrees and the wind blowing with sideways snow this morning.

uncle ned

Hope to see every one at jacks if all works out. will be leaving nc on the 26th.  321, 301, 17 then i don't know any thing but the interstate.
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« Reply #20 on: December 07, 2007, 01:50:16 PM »

Guys...I hate getting middle age. (old?)  Forgot you have a 2-stroke Detroit and not a Cummins.  Sorry.  In my old school bus driving days, the mighty idling 743 inch 220 Cummins in the 1963 Crown school bus would instantly stall if you let your foot off the gas pedal when the Jake was turned on.  Some switch wasn't working right.

The school bus mechanics were aware of it, but just told me to turn off the Jake when in town soosss that would not happen.  Also a neat thing about the Jake is that, after the oil gets a chance to warm up and the thing works, you could "burp" the engine while double clutching upshifing.  Very cool and the kids loved it.

This was considered abusive and not advised,  but from time to time I did it anyway, since it allowed me to up-shift under conditions that would normally be considered difficult or impossible, like climbing a short, steep hill.  Spicer 5-speed.  Anyway, the Jake Brake is one of the world's greatest inventions---next to red wine.  He he he.  Smiley Smiley Smiley
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« Reply #21 on: December 07, 2007, 05:09:10 PM »

Nick:
   your millage is tied to your tune up. What were the injector settings before they installed the jakes. Go back to that setting and see if your millage returnes. You may also have an injector that is dribbling fuel into the cylinder when it is in the no fuel position ( foot off the go pedel ) comming to a stop or down hill operation with the jakes on.

Hope this helps

Don
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« Reply #22 on: December 08, 2007, 09:34:24 AM »

Nick .... do I see a trip out west to Don's shop coming up in the future HuhHuh LOL. Hard to find a good 2 stroke mech ...
Ron
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« Reply #23 on: December 08, 2007, 10:03:27 AM »

Nick .... do I see a trip out west to Don's shop coming up in the future HuhHuh LOL. Hard to find a good 2 stroke mech ...
Ron

I hope so! I would love to see Nick's bus!
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« Reply #24 on: December 08, 2007, 10:30:14 AM »

Jakes on a mechanical 2-troke do not shut off the fuel. Jakes turn with the on/off swich in low, med., or high position, throttle switch closed and clutch switch closed. All 3 things have to met when jake work and a mechanical fuel system. The engine still has fuel fuel being injected even w/ no power stroke, and with the eng idling and all 3 switches set, it is normal for the eng to die if the on/off switch is left on. Electronic engines have no fuel injected at idle do to jakes are controlled by the computer, fuel is shut off by fuel solenoids completely. The mileage issue mentioned is directly relative to temp and driving condtions, wind, cool or warm weather, into the wind, w/ the wind, etc. The wurst wind condition to affect milage is a 45 degree cross wind.
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« Reply #25 on: December 10, 2007, 02:43:39 PM »

jakes don't shut off fuel they stop fuel from being injected into the cyclinder by way of a plunger and fork on the injector rocker The rack on an mui engine will go to no fuel for a short time when you take your foot off the throttle. The gov will pick up the rack and return it to a fuel spot in relation to the throttle setting. ie idle, fuel rpm or any spot inbetween depending on foot position. Lets say you are crussing down the road at 70 mph and you come up on a construction zone and the posted speed dropes to 40mph. You remove your foot from the throttle and coast, the rack will go to no fuel until either your foot goes back on the throttle or the gov. picks up the rack to set the proper rpm.  You are corect about the wind. It has an effect on any box we drive down the road.

In nicks case he had a jake added to his engine and the millage was affected. This is why I said his problem is tuneup related. When the jake was added they should have retuned the engine and if they changed injector settings from lets say 1.520 to 1.470 this will have an effect on the way the engine runs. You must take in account the camshafts, blower (83% vs 100%) and turbo that is on the engine.

hope that better explanes where I am comming from.

Don

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Nick Badame Refrig/ACC
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« Reply #26 on: December 10, 2007, 03:19:53 PM »

Hi Don,

Yes, I understand what you are saying. It makes perfect sence!

I don't know the injector settings but, the engine runs like a "Raped Ape"  Shocked  So, I'm not going to complain anymore...

Thanks for your help!
Nick-
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« Reply #27 on: December 11, 2007, 03:25:33 AM »

Nick,

Don is right on with his statement I have installed over 500 sets of Jakes and never heard of a loss of fuel mileage. It is usually due to short circuit from left side of brain to connection to right foot. As you say it runs like a raped ape it was due to valve adjustment (ie tuneup) with installation of jakes. One person stated that valve clearance got greater when engine warmed up and that is just the opposite when the engine heats up valve clearance will decrease with the expansion of the metal parts. You want the ponies you got to feed em.

LarryH
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« Reply #28 on: December 11, 2007, 09:33:42 AM »

Maybe I got confused here - Are you all saying that operating continuously with your jake on will NOT affect fuel mileage?
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