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Old 08-09-2013, 01:40 PM   #1
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Freightliner Owners Club
Join Date: Nov 2012
Posts: 2
Engine Brake Delay Problem

Our 2005 Winnebago Vectra, Freightliner Chassis, Cummins ISL 8.9 L 400 HP, coupled to a 3000 Allison Transmission has a hard to diagnose Engine Brake delay. We have had it to some reputable shops, and they changed the engine ECM to get the engine brake to function as it does now, but it worked correctly when we bought it in 2012.

The delay is from 5 to30 seconds before engaging,
on decreasing speed(accelerator at 0 %), in 6th gear - it rarely comes on;
In 5th gear, it comes on at 35 MPH - after downshifting to 4th gear;
In 4th gear, it comes on at 26 MPH - after downshifting to 3rd gear;
In 3th gear, it comes on at 19 MPH - after downshifting to 2th gear;
the engine always seem to be around 1060 RPM when engaging the Engine Brake.

If anyone has a suggestion, or know of a shop that has a wizard on the CAN bus, I would appreciate it.

David J. Anderson

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Old 08-09-2013, 07:32 PM   #2
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Join Date: Mar 2012
Location: Palmer Ak
Posts: 1,089
Have you had the tranny hooked up to a computer? On our last motor home, the trany needed to have some internal work and they had reprogramed it. When I picked it up I was not happy with the engagement of the exhaust brake. The shop hooked up a computer to it an reset the engagement of the exhaust brake. It was much better.
I would take the MH to an Allison shop and see what they can do.

2009 38' Diplomat
CSM- retired, wife as co-pilot
Reka & Ali providing security (our 2 labs)
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Old 10-01-2013, 09:38 AM   #3
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Engine Brake Fixed

Our Cummins_ISL03 with Allison_CBRAKE_Jacobs490 engine brake problem on our 2005 Winnebago Vectra on a Freightliner Chassis is solved. The engine brake works great now!

Problem was apparently incompatibility of engine ECM firmware revision from A to W when ECM replaced. I had to replace the Intake Manifold Pressure Sensor. The change I observed was that the old sensor was an Absolute Pressure Sensor, and the new one is a Relative Pressure Sensor. My boost gauge before changing started at 15 psi with the engine not running, and would get up to about 35-40 psi at full power. Now the boost gauge starts at 0 psi with the engine not running, and will go up to at least 50 psi at full power, and is much more active than it was.

Neither Cummins or Allison seemed to have a bulletin noting this incompatibility.

It seems that the Allison control to the engine is only to allow the engine brake when the converter is in lockup - all the other control is in the Engine ECM.

Any comment?
D Anderson, 2005 Winnebago Vectra
Cummins 8.9 L ISL, 3000MH Allison
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Old 10-02-2013, 05:59 PM   #4
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Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 11,950
Comment: To error is human ; It takes a computer to really sc..w things up.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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