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Old 10-22-2017, 01:06 PM   #1
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VGT turbo brake issue

I have an entegra motorhome with a Freightliner chassis and a Cummins ISL 400 engine. After making it to the mountains out west I realized the exhaust brake was not working. The transmission would downshift as it is supposed to but still completely failed to control my speed on any grade above 4%. I tested the functionality by going down a grade and manually shifting into a gear that brought me to 2500 RPMs and then toggled the exhaust brake switch on and off with absolutely no noticeable difference in deceleration. I took it into Freightliner in San Diego and after hours of testing they told me that I don't actually have an exhaust brake I have a turbo brake, and that the turbo brake really doesn't do anything. I called Cummins tech support and was informed that the turbo brake actually only helps my braking 1 or 2% and I probably would not feel any effect whether it's on or off. Is my RV the only one that has this useless auxiliary braking?
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Old 10-22-2017, 03:25 PM   #2
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You are being fed a "crock of crap" the VGT system does
noticeably improve speed reduction along with the downshift.
When it is engaged, you will feel it. However you must apply the service brakes momentarily to engage it, with the switch in the on position.
However, if you just hit the switch, and do not engage
the service brakes it is not programmed come on.
Alternate programming can tell the ecm to engage the VGT
when the switch is on and you remove your foot from the throttle, but this prohibits coasting.
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Old 10-22-2017, 06:42 PM   #3
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this turbo or normally called exhaust brake has been around for many years & work great when used regularly.this is why cummins & freightliner continually issue the wrong info only due to their ignorance of their own product.
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Old 10-22-2017, 06:49 PM   #4
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Agree... only had mine a short time but it activates when I remove foot from accelerator...more if I apply brakes and especially if I also downshift. Definitely can tell the difference on or off.
First 50 or so miles was over the mtns from Ashville NC..
Only needed scv brakes 1-2x down the mtns... worked very well for me.
'13 Ventana w 360 HP ISB
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Old 10-22-2017, 08:03 PM   #5
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Thank you for the replies, I have tried every combination of braking with switch on and cruise control off . The guys at San Diego Freightliner said the computer showed all working properly. What I know is I have to get on the brakes constantly on any grade.The recommended solution I was given was to add an exhaust brake. I will pursue this further after your responses, I really don't want to get new brakes every 10,000 miles.
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Old 10-22-2017, 08:09 PM   #6
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Can anyone give a comparison to an exhaust brake?
Thanks
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Old 10-22-2017, 08:35 PM   #7
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My 09 has an exhaust brake AND a VGT.
Confused
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Old 10-22-2017, 10:30 PM   #8
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Are you SURE you have a VGT/exhaust brake?

Most ISLs of that era had a 2-stage Jake brake (a true compression brake) not an exhaust brake.
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Old 10-22-2017, 11:14 PM   #9
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Your 2016 ISL should be a 450ISL. I have a 2006 400ISL and I has a 2 stage jake brake (integral to valve train) which retards engine (engine brake). It sounds like something is not working correctly on your jake brake setup.

The Cummins ISL also programs the VGT to engage and provide boost to supplement engine retarding.

The 400ISL does not have a separate exhaust brake.

You can search YouTube for Jake brake operation (Jacobs Engineering).

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Old 10-23-2017, 09:21 AM   #10
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Turbo brake only according to Freightliner. It has a single position switch. I did ask Freightliner if it might be programmed to only activate when applying service brakes and they said no. I must say that the service brakes are amazing, but I don't want to cook them or the Sprinter brakes with the air force one on the long grades. I will try to get specs from Cummins today.
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Old 10-23-2017, 01:15 PM   #11
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Quote:
Originally Posted by kwoods View Post
Turbo brake only according to Freightliner. It has a single position switch. I did ask Freightliner if it might be programmed to only activate when applying service brakes and they said no. I must say that the service brakes are amazing, but I don't want to cook them or the Sprinter brakes with the air force one on the long grades. I will try to get specs from Cummins today.
Once again, BAD info from someone at a Freightliner shop.
The exhaust brake can be programmed to come on when
you lift your foot from the throttle OR to come on when
you apply the service brakes.
I know this for a FACT, since I had mine re-programmed
to come on with the brake application, thus allowing me to
coast when I wanted to in certain situations. Try to find
your local "Thomas Built Bus dealer" they will know
your chassis better than any Freightliner shop that mainly
works on truck tractors.
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Old 10-23-2017, 06:28 PM   #12
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I had mine reprogrammed by Cummins to activate if the brake pedal was tapped and go off when the accelerator is depressed. Suggest you try Cummins as their software is required to make the change.
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Old 10-25-2017, 07:12 PM   #13
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So far Cummins tells me that the mean brake effect is 279 psi, trying to get what that means in hp. Does anyone else have just a VGT Turbo brake, no Jake or exhaust brake also?
Thanks again
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Old 10-25-2017, 07:33 PM   #14
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Quote:
Originally Posted by kwoods View Post
So far Cummins tells me that the mean brake effect is 279 psi, trying to get what that means in hp. Does anyone else have just a VGT Turbo brake, no Jake or exhaust brake also?
Thanks again
Yes!
And, if you look up your engine on Cummins website, you cant install a standard restrictor style exhaust brake behind the VGT turbo brake!
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