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Engine Brake Problem or Different. Help Please!


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We have a 2005 Safari Cheetah 40DST with a CAT C7 engine and 6 spd Allison Transmission. I have previously had a few issues with the acceleration not working and the RV belching out black smoke. I was subsequently told the problem was that I was running the exhaust break at low idle. I quit using the exhaust break except in emergencies. Went about 9 months without an issue. A few days ago I experienced an emergency stop on the interstate and used the E. Break. after stopping I turned it off. When traffic started to move again the RV would not move when the engine rev'ed and black smoke bellowed out the exhaust. After shutting down and allowing some time I restarted the engine, idled a while and then drove off with a little black smoke and then all was well. I have since driven about 600 miles with out incident.

My questions for you more experienced DP owners: 1) Is this normal?

If not, Do I have a defective E. Break or is there another issue?

Note: I did not through any codes on my D-Scanguage. I had a full work up following the insolent prior at a Caterpillar Service center and they found nothing to report.

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What you were told is a bunch of horse feathers about your engine brake. Have it checked and lubed sounds like lack of lube could be the problem you should be able to leave it on at all times and enjoy its benefits 

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When I first started using my exhaust brake about 3 months ago, I felt like it might be sticking a little.  I used it going down a hill and when I started back up the next hill it seemed to me that I didn't have quite as much power, so I turned it off.  I did some reading on the subject and decided that I needed some of the special lubricant that is recommended for the exhaust brake.  I ordered some, but couldn't really find where I needed to apply it.  I wish someone could show me exactly where the lube needs to go.  I've crawled under the coach, but I can't find the spots that need the lube.  I just decided to turn the E brake on and leave it on all the time.  It just needed to be used a little and now it works great.  I just got back from a 10 day run through New Mexico and Colorado and it really worked great descending some of the steeper hills.  Even just slowing down as we came into some of the small towns along the highway it worked really well.  I have a 5.9 Cummins ISB and a 5 speed MH2500 tranny and if I am traveling at about 65mph when I take my foot off the throttle it will downshift to 4th and if I let it continue to slow down it will then downshift to 3rd and then shortly after that to 2nd.  If you plan ahead just a little, you almost don't need to use the service brakes.  If I just want to slow down a little and keep it from downshifting to 3rd, all I have to do is keep the slightest pressure on the throttle.  With just a little practice, you can learn to use it very effectively.

Carey

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Can't say this applies to either posting but following my owner's manual for service I too bought the special high temp lubricant and began a search for the elusive "exhaust brake".

There were no forums to help them or I did not find them. After contacting Cummins I was informed I have a VRT turbo and not an exhaust brake. Variable ratio turbo.

I don't remember precisely how it works but it sure does and is on about 99% of the time.

As for power climbing hills. If you have the Economy feature on your shifter panel, turn it off for the best acceleration performance. It will stay in a lower gear for a longer period. It is nearly impossible to detect any fuel improvements when using it. 

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1 hour ago, myrontruex said:

Can't say this applies to either posting but following my owner's manual for service I too bought the special high temp lubricant and began a search for the elusive "exhaust brake".

There were no forums to help them or I did not find them. After contacting Cummins I was informed I have a VRT turbo and not an exhaust brake. Variable ratio turbo.

I don't remember precisely how it works but it sure does and is on about 99% of the time.

As for power climbing hills. If you have the Economy feature on your shifter panel, turn it off for the best acceleration performance. It will stay in a lower gear for a longer period. It is nearly impossible to detect any fuel improvements when using it. 

Myron, if you have a Cummins engine, you likely have a VGT (Variable Geometry Turbo).  In 2008, the actuator was electronic.  The exhaust gas opening is adjusted to control the geometry of where the exhaust gas hits the turbo vales to control boost pressure.  When the opening is nearly closed, it basically goes into an exhaust braking mode.

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12 hours ago, 1nolaguy said:

We have a 2005 Safari Cheetah 40DST with a CAT C7 engine and 6 spd Allison Transmission. I have previously had a few issues with the acceleration not working and the RV belching out black smoke. I was subsequently told the problem was that I was running the exhaust break at low idle. I quit using the exhaust break except in emergencies. Went about 9 months without an issue. A few days ago I experienced an emergency stop on the interstate and used the E. Break. after stopping I turned it off. When traffic started to move again the RV would not move when the engine rev'ed and black smoke bellowed out the exhaust. After shutting down and allowing some time I restarted the engine, idled a while and then drove off with a little black smoke and then all was well. I have since driven about 600 miles with out incident.

My questions for you more experienced DP owners: 1) Is this normal?

If not, Do I have a defective E. Break or is there another issue?

Note: I did not through any codes on my D-Scanguage. I had a full work up following the insolent prior at a Caterpillar Service center and they found nothing to report.

Do you know what make/model of exhaust brake do you have???

Not using the exhaust brake will/has result in problems in that it get stuck.  Read about this happening all the time.  I have a PacBrake and I use mine religiously.  It does a good job of braking.  I also lubricate it base on the manufacturers recommendations.  I bought a bottle of the recommended lubricant 13 years ago, it goes a long ways.  Doesn't take long to do, I remove the rod on the air cylinder and work the butterfly valve by hand to make sure it works. 

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3 hours ago, myrontruex said:

Can't say this applies to either posting but following my owner's manual for service I too bought the special high temp lubricant and began a search for the elusive "exhaust brake".

There were no forums to help them or I did not find them. After contacting Cummins I was informed I have a VRT turbo and not an exhaust brake. Variable ratio turbo.

I don't remember precisely how it works but it sure does and is on about 99% of the time.

As for power climbing hills. If you have the Economy feature on your shifter panel, turn it off for the best acceleration performance. It will stay in a lower gear for a longer period. It is nearly impossible to detect any fuel improvements when using it. 

This is one of the best videos I've found that explains the different types of turbo chargers Cummins used.  There is also a good visualization of a waste gate and variable geometry turbo with the VGT also being able to function as an engine brake.

 

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On 10/14/2022 at 11:08 PM, Idoc57 said:

When I first started using my exhaust brake about 3 months ago, I felt like it might be sticking a little.  I used it going down a hill and when I started back up the next hill it seemed to me that I didn't have quite as much power, so I turned it off.  I did some reading on the subject and decided that I needed some of the special lubricant that is recommended for the exhaust brake.  I ordered some, but couldn't really find where I needed to apply it.  I wish someone could show me exactly where the lube needs to go.  I've crawled under the coach, but I can't find the spots that need the lube.  I just decided to turn the E brake on and leave it on all the time.  It just needed to be used a little and now it works great.  I just got back from a 10 day run through New Mexico and Colorado and it really worked great descending some of the steeper hills.  Even just slowing down as we came into some of the small towns along the highway it worked really well.  I have a 5.9 Cummins ISB and a 5 speed MH2500 tranny and if I am traveling at about 65mph when I take my foot off the throttle it will downshift to 4th and if I let it continue to slow down it will then downshift to 3rd and then shortly after that to 2nd.  If you plan ahead just a little, you almost don't need to use the service brakes.  If I just want to slow down a little and keep it from downshifting to 3rd, all I have to do is keep the slightest pressure on the throttle.  With just a little practice, you can learn to use it very effectively.

Carey

If I read your post correctly, you said you left the Exhaust Brake ON AT ALL TIMES.  I would only point out that we have had a member that was told that by the previous owner.  He then did that and had to have the DPF replaced.  I would recommend that you contact Cummins Tech Support or an authorized Cummins Service Dealer.  The Exhaust Brake, per MY understanding, is to be used NORMALLY, but NO LEFT ON ALL THE TIME. 

YES, there are individuals that do so.  I rode in a tour bus with a seemingly experienced driver and was in the front seat. He was in stop and go traffic as we entered NYC and he left on the Exhaust brake for about 30 miles. 

PERSONALLY, I use mine frequently going downhills and when I approach an interstate exit.  In 45 MPH Suburban traffic, if it is somewhat heavy and the lights are prone to change quickly, I will leave it on.  I guess that I do use it a bit more often then others.  I recently had to replace the Carling Switch Operator (Exhaust Brake switch plastic "cover"). But I have not had any issues with my ISL 425 and It has almost 67K on it and when Frank MeElroy pulled the Insite data on my engine, there were no issues....that was around 50K or so.

Just passing this on.  Read the last comments on so from "Daryl".  Frank was helping him out over the phone and I contacted him also as we probably met a few times as we lived in the same small NC town and our paths would cross.  Daryl had the DPF replaced.  He found a REAL Cummins Dealer and had all the tests run. He drove back to NC from CO without any issues. He MAY have a hesitation or a Turbo Lag issue....but NOT the plethora of issues that the "Independent" shop quoted him. He is very happy and can address that locally. Both Frank and I talked to him during or at the end of his trip.

 

 

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22 hours ago, myrontruex said:

Can't say this applies to either posting but following my owner's manual for service I too bought the special high temp lubricant and began a search for the elusive "exhaust brake".

There were no forums to help them or I did not find them. After contacting Cummins I was informed I have a VRT turbo and not an exhaust brake. Variable ratio turbo.

I don't remember precisely how it works but it sure does and is on about 99% of the time.

As for power climbing hills. If you have the Economy feature on your shifter panel, turn it off for the best acceleration performance. It will stay in a lower gear for a longer period. It is nearly impossible to detect any fuel improvements when using it. 

Myron, I have the ISL and this is MY OBSERVATIONS....as well as experiments.

The VGT Exhaust Brake does NEED exercising.  I use mine (see previous posts) normally or maybe a bit more....but do NOT leave it on for extended periods of time.

I have traversed some of the worse grades outwest.  I used the "Mountain Guide" books and planned my trips and did not take the routes known to be BRAKE KILLERS.  But, I did do the drop through the Eisenhower pass west of Denver on I70 and actually found one that was just as bad on a highway 12 in Utah (going from Torrey to Cannonville) and it was NOT in the guide. So, even without the 2 position Jacob's Brake, you can do OK. BTW....if you EVER want a scenic "Ride of your LIFE"....do it.  The view from a MH cab really adds a bit of a "thrill" to it.  Ask my DW and 50 YO son....

https://capitolreef.org/scenic-byway-12/

 OK....next.  The Economy Mode, in my experience, WILL improve your mileage.....if you use it like I do. I drive around 63 MPH using the cruise on the Interstates.  That is about 2 miles FASTER than my normal (performance or economy mode) upshift from 5 - 6.  The Allison TCM was programmed by a committee from Allison, Cummins and Monaco. That is where the engine gets it peak torque....or the sweet spot. You can calculate it from the tire rev's per mile, Differential Ratio and the Transmission gear ratios. SO, if you go slightly higher, it will give you Max Fuel Economy.  

NOW, having said that, I use the ECONOMY setting with CRUISE on the Interstates. The Economy setting does NOT impact the UP SHIFT....but it seems (my observations and experiments) to impact the DOWN SHIFT from 6 to 5.  I have traveled the same stretch or similar "slightly hilly" stretches and use PERFORMANCE as well as ECONOMY.  The Allison will allow you to drop down to maybe 56-58 MPH and NOT downshift.....but in Performance, it will downshift almost immediately at 60 or so.  SO, you gain about 3 - 4 MPH of  "tolerance" and that is definitely a fuel saver.

Finally, the VGT or Exhaust Brake is a KILLER if you leave it on with Cruise. Monaco did some STRANGE things.  Frank McElroy experimented with my ECM parameters. His Dynasty's Exhaust Brake "disengage" when you tap the service brake and disengage the CRUISE.  Mine will NOT.  Mine stays on.  SO, I have to be cognizant that if I start down a grade....and the cruise is ON and turn ON the CRUISE, there will be SOME interaction and the CRUISE will start to back off to control the ENGINE....but it will accelerate and typically, I tap the brakes to disengage the Cruise....and that has a marked impact of deceleration.  BUT, i also have to remember to turn OFF the VGT Exhaust Brake when I get back on level highway. I have mistakenly left if on and it will knock about 10% off the MPG as the brake cuts in and out as the cruise cycles.  You barely feel it....so I am alert and try to NOT to leave it on.

Again, that is MY experience....over 65K or so.  OTHERS with different engines, perhaps, might be different.  Obviously Frank's Dynasty ISL 425 has a different operating logic...

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Interesting Tom. I mostly just ignore mine because of very little noticeable interaction. If long and flat runs I use the Econ mode but for any sort of hills, not just rolling ones and I turn it off. 

My Exhaust brake only gets turned off in traffic which allows me to coast a bit. 

That video is the best one I have seen as well. I always wondered how they made them variable ratios. Trying to find my darn exhaust brake to lube it was comical. But then I looked for the plug that seemed to be missing from my transmission housing as well.

My incredible FIL had passed just a year or so before buying out DP. He was a lifelong diesel mechanic and would have had some fun at my expense but would have been very proud to know we bought a Cummins. 

As for the pronunciation of Cummins. I was surprised to hear the narrator of the video call the company "Cummin(g)s. This is how my FIL pronounced it as well. Seems some folks get their knickers in a wad when pronounced that way. 

I can remember my FIL and his fellow truckers bragging when they could get their 330 Cummins boosted to 350's.. As memory serves me, it has been fifty years. They were hauling 40-ton rocks at times (maybe more when the inspectors weren't looking), and trying to make it up any hill just a truck length to be in line for the first load or last load of the day. Great memories for sure.

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10 hours ago, 1nolaguy said:

Not aware the E break was added. I thought it was part of the CAT7 engine. Where do I look to determine the E Break brand/model?

Take some pictures of the exhaust circuit including the Turbo. 

I tried to look on line doing some searches for exhaust brake on a 2005 Safari with the Cat 7 but could not find anything definitive. 

Here is a link to a PacBrake, it would be pretty easy to see if you had one.  https://pacbrake.com/product-lines/exhaust-brakes/

This is what I have and I use it all the time but do not leave it on.  If you leave it on while driving in stop/go traffic every time you take your food off the accelerator the brake comes on causing a jerk.  So you can't coast at all.  IMHO I believe that would impact your fuel economy. 

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The VRT on mine kicks out around 6-10 mph for braking and is a very smooth transition. It is noticeable but smooth. 

Doing acceleration tests many years ago I found I could get to a certain speed quicker with the Econ mode off versus on. Changes shift points. But noticeable for sure and measurable. I turn mine off when getting onto freeway traffic for example for best ability to get to speed.

Changing my RR fan to one from source changed my acceleration and dramatically improved economy by 1 mpg but don't want to wander off on this one. If interested PM me. 

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Jacwjames, I will try to take some photos today and post them. My rig has a radiator in the back and on the side so all photos need to be taken from underneath. At 68, getting up is the hard part but I will look underneath.

Tom Cherry, in my set up I can engage the speed control or the exhaust break but not both at the same time. If I turn on the E Break the SC does not function.

Note: there was a comment(s) above about leaving the E Break on full time. I do not do this. Only tun it on when it is needed. I use to leave it on except when using CC. That is when I had the first issue and was told not to leave it on during low RPMs. Just want to clear this up in case there was any misunderstanding from my OP.

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On our 05 Dip, CC won't engage if E-brake is active. Use mostly exiting highways and some grades (we live in the west so fair number of those). In city driving it's off and drive in 3 or 4th as E-brake is too touchy

 

 

 

 

 

 

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Same here. Do not understand the heavy black smoke once used. Maybe as noted previously it is an oil issue but I need to find the E Brake first then figure out how to oil it.

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3 hours ago, myrontruex said:

Interesting Tom. I mostly just ignore mine because of very little noticeable interaction. If long and flat runs I use the Econ mode but for any sort of hills, not just rolling ones and I turn it off. 

My Exhaust brake only gets turned off in traffic which allows me to coast a bit. 

That video is the best one I have seen as well. I always wondered how they made them variable ratios. Trying to find my darn exhaust brake to lube it was comical. But then I looked for the plug that seemed to be missing from my transmission housing as well.

My incredible FIL had passed just a year or so before buying out DP. He was a lifelong diesel mechanic and would have had some fun at my expense but would have been very proud to know we bought a Cummins. 

As for the pronunciation of Cummins. I was surprised to hear the narrator of the video call the company "Cummin(g)s. This is how my FIL pronounced it as well. Seems some folks get their knickers in a wad when pronounced that way. 

I can remember my FIL and his fellow truckers bragging when they could get their 330 Cummins boosted to 350's.. As memory serves me, it has been fifty years. They were hauling 40-ton rocks at times (maybe more when the inspectors weren't looking), and trying to make it up any hill just a truck length to be in line for the first load or last load of the day. Great memories for sure.

TO CLARIFY, I only use my VGT Exhaust brake when I want to "stop or slow down"  For instance, if I am coming up on an interstate exit, I plan ahead and tap the brakes.  That disengages the CC. Then I switch on the Exhaust brake. That gives me a good bit of Deceleration....and typically, if I time it right, will be around 20 MPH as I enter the exit. I hardly ever use the service brake on the interstate....

I use it around town if there is heavy stop and go traffic.  I may leave it on for a few closely spaced stop lights.

Obviously I use it full time for long grade descents. Like the Eisenhower pass or Black Mountain in NC just outside of Asheville.....or when I am in the mountains and it is rolling.  On descents....I click it OFF right before I hit the bottom or when it gets close to my desired or CC set speed.

The ONE thing that I have observed and don't think it is an issue.  I recently noticed a rough "Downshift" with the Exhaust brake as it interacts with the Allison and downshift it to 2 or 3 and that adds more braking power.  I checked the Allison's Oil level using the Key Pad.  OL OK was the message. An Allison tech had told me there was a broad range of OK OL.  So I added a pint of Transynd....that helped....Drove it....leveled it....and checked....  OL OK sill there.  So, I added maybe another pint....total of no more than a quart.  BINGO, shifts like a dream. STILL OL OK on the key pad.  I had had it changed in early 2018, but the tech let it drain for a LONG time.  OPPS, said the Allison Tech. Our "19 Quarts or so is based on an immediate filter and pan replacement.  I had a LO 3 as in THREE quarts.  He said to NOT believe it and go slowly....a pint at a time.  When I got to OL OK....maybe a quart more.  So, I may NOT have added enough and that was 12K miles ago.

All I know is that it shifts like a dream now and it works as expected and is effective.  NOT a Jabob;s but good enough my driving and also the terrain....and I plan ahead.

I have not had my brakes measured, but I doubt I have hardly any wear.

The rest is what I do know about the VGT and its impact on fuel economy in CC.

The folks that have a different "setup or configuration" with their cruise and exhaust brake are just another example of Monaco's lack of consistency.  Try as Frank might, he did NOT reprogram the ECM to disengage the CC when the brake was applied.  My tapping the brake pedal works....

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  • Tom Cherry changed the title to Engine Brake Problem or Different. Help Please!
11 hours ago, Tom Cherry said:

The folks that have a different "setup or configuration" with their cruise and exhaust brake are just another example of Monaco's lack of consistency.  Try as Frank might, he did NOT reprogram the ECM to disengage the CC when the brake was applied.  My tapping the brake pedal works....

Tom - Your engine ECM has a feature called cruise control auto-resume and that feature is disabled.  That means it is configured to not resume the cruise control once the service brake is activated.  Also, when your VGT engine brake is activated, it is configured to turn on your rear brake lights.  So, the ECM is configured correctly.

I can think of two reasons why the cruise control automatically resumes when you activate the engine and then turn it off.  It's either an inherent feature on engines with VGT engine brakes (there is no ECM option to change it), or the coach was never wired to interconnect the cruise control cancel when your engine switch brake is activated.  The service brakes will disengage your cruise control as per ECM settings.

On my Dynasty there is a wire on the engine brake switch that sends a signal to cancel the cruise control once the Jake brake switch is activated.  That's why on mine you can't engage the cruise control if the Jake brake switch is turned on.  I've looked at your wiring diagrams and on page 36 there is NO wire on your engine brake switch going over to cancel the cruise control like there is on my schematic.  So, to me this looks like a wiring decision (maybe a feature they wanted or an error) made by Monaco when your coach wiring diagram was designed and not an engine ECM configuration issue.

Maybe others with the same coach as yours will chime in.

 

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9 hours ago, Frank McElroy said:

Tom - Your engine ECM has a feature called cruise control auto-resume and that feature is disabled.  That means it is configured to not resume the cruise control once the service brake is activated.  Also, when your VGT engine brake is activated, it is configured to turn on your rear brake lights.  So, the ECM is configured correctly.

I can think of two reasons why the cruise control automatically resumes when you activate the engine and then turn it off.  It's either an inherent feature on engines with VGT engine brakes (there is no ECM option to change it), or the coach was never wired to interconnect the cruise control cancel when your engine switch brake is activated.  The service brakes will disengage your cruise control as per ECM settings.

On my Dynasty there is a wire on the engine brake switch that sends a signal to cancel the cruise control once the Jake brake switch is activated.  That's why on mine you can't engage the cruise control if the Jake brake switch is turned on.  I've looked at your wiring diagrams and on page 36 there is NO wire on your engine brake switch going over to cancel the cruise control like there is on my schematic.  So, to me this looks like a wiring decision (maybe a feature they wanted or an error) made by Monaco when your coach wiring diagram was designed and not an engine ECM configuration issue.

Maybe others with the same coach as yours will chime in.

 

No argument here.  If your ECM changes didn’t correct, it has to be an external wiring, as in the Exhaust Brake or other circuits.  As we discussed after trying out the MH with your changes, the efforts to modify or revise my Exhaust Brake switch, would or could be time consuming….and even though the prints are available, this one “lack of a feature” is probably not worth the resources and efforts to pursue.

Since I’ve done the Bucket List driving in all lower 48 and camping in 47 and met my goal of 60 nights, average, per  year and 6K miles in the ten seasons from 2009 - 2018 and had my younger, but not in college or finishing HS and have a “life of their own”, I won’t be doing that much travel.  So. It is what it is. 

I do appreciate you trying and now resolving the wiring issue….

Wish I could con someone into installing the Jacob’s brake…..but, alas, my efforts seem to be failing….but I keep trying….LOL!

Thanks for the detailed explanation and the recent research….

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I have been a previous owner of a 2005 CAT C7 powered motorhome.  Mine had the Pacbrake brand exhaust brake, I suspect your is the same.  The first time I used it, it closed the cast iron flapper and it stuck closed (it had evidently not been used by the previous owner).  I had to crawl under and take a hammer to knock it back open.  When I got home, I took the exhaust brake off and soaked it in solvent and worked all the rust out.  With proper lubrication, it worked correctly for the rest of the time I owned that motorhome.  If exhaust brakes are not used regularly, they will rust up and seize.  Cleaning and lubricating becomes important. 

Richard

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12 hours ago, Tom Cherry said:

No argument here.  If your ECM changes didn’t correct, it has to be an external wiring, as in the Exhaust Brake or other circuits.  As we discussed after trying out the MH with your changes, the efforts to modify or revise my Exhaust Brake switch, would or could be time consuming….and even though the prints are available, this one “lack of a feature” is probably not worth the resources and efforts to pursue.

Since I’ve done the Bucket List driving in all lower 48 and camping in 47 and met my goal of 60 nights, average, per  year and 6K miles in the ten seasons from 2009 - 2018 and had my younger, but not in college or finishing HS and have a “life of their own”, I won’t be doing that much travel.  So. It is what it is. 

I do appreciate you trying and now resolving the wiring issue….

Wish I could con someone into installing the Jacob’s brake…..but, alas, my efforts seem to be failing….but I keep trying….LOL!

Thanks for the detailed explanation and the recent research….

Most folks likely don't know this but on many of the newer Cummins engines there is an ECM option that Monaco rarely used.  It is a setting to allow the cruise control to interact with and automatically apply the engine brake when the coach speed exceeds the cruise set speed by a set amount. 

If the "Cruise Control and Engine Brake Interaction" feature is Enabled, you can set the speed above the cruise control set speed where the engine brake would activate and if a two stage engine brake the speed where the second stage would activate. 

On my coach, I enabled that feature and set the Low Jake brake to activate at +5 MPH  and High Jake to activate at +8 MPH above the cruise control set speed.  For this feature to work, the cruise control Auto Resume feature must also be Enabled. 

So, if I have my cruise control set at my normal 62 MPH and I'm going down hill, once I get above 67 MPH, the low Jake brake would come on; if above 70 MPH, the high Jake would come on.  Then once the speed got to my set speed of 62 MPH, the cruise control would resume. 

I like it.  If other want it, you need a shop with the Cummins Insite software to make changes in the Features and Parameters settings of the ECM.

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The exhaust brake flapper mechanism with it's actuator would be installed on the drivers side of the engine right close to the turbocharger.  I am currently running a CAT C9 (big brother to the C7) and it is set up the same way.  Many of the Cummins engines installed on other Monaco branded motorhomes use totally different exhaust and engine brake systems.  When Monaco acquired SMC (Safari and Beaver coaches), SMC was contracted with CAT to provide engines.  That is why most Monaco motorhomes have Cummins engines, but the Safari and Beaver derivatives were CAT.  Hope that all makes sense.

Richard

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The exhaust brake can malfunction and not open(release) for a couple of reasons.  One the valve stem will be stuck, and it doesn't move freely and needs lubrication as stated earlier.  The other is related to the electrical set-up on the brake and its connection to the coach brake lights.  The exhaust brake activation circuit is connected to brake lights to signal when the exhaust brake is activated, causing the lights to come on.  The ground connections in the rear light housing can go bad, which then causes feedback to exhaust brake. When the exhaust brake is activated, power goes to the air solenoid valve, then the valve will be held open by the low voltage from the taillights if on.  Yes, this sounds unlikely, however, I actually helped an owner who was experiencing this.  The exhaust brake wouldn't release with the headlights on and then release when the lights were turned off.  After some emails he experimented with his unit and the solved the problem by fixing the ground.  Incidentally he was in Alaska on a caravan and had spent a lot of money trying to solve it.

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