Reduced exhaust braking after demandate

[jaysoto]

This is for a L9 with only the exhaust brake so I apologize if I put this in the wrong section but basically overall the truck runs fantastic since I demandated it great fuel economy great power everything is great except it seems like my exhaust brake is weaker than it was before. Just curious if this is because there is less back pressure? Or if anyone else has noticed it. Is it controlled in the tune where you could in theory make it work better? Turbo and actuator are good I just replaced the actuator this spring before the demandate and it works and tests fine. Another thing is if I'm at 1900rpm and I let out of the throttle and the exhaust brake kicks in the turbo flares a bit like it kicks in strong then backs off then back to strong. I believe it's always done that but I really don't feel any braking ability until I get down to maybe 1300rpm. It seems like at that point the exhaust brake is fully engaged/vanes fully closed. Maybe I'm overthinking but I would bet hands down it was stronger before. Thanks

[Rawze]

If your able to back up/restore the ecm yourself, then take it on a test drive and screen record what its doing (using the 'OBS studio' software).

While recording, in Insite, monitor the following live data ...

== the engine brake status for stage 1,2,3
== the turbo position commanded
== the turbo position measured.
== Boost level.
== Exhaust pressure level.
== fuel pedal position.

.. then flash the clean factory programming back in it temporarily and do the same recording and same test drive to see if the engine brake and turbo are acting similar.

[jaysoto]

(08-13-2026 )Rawze Wrote:  If your able to back up/restore the ecm yourself, then take it on a test drive and screen record what its doing (using the 'OBS studio' software).

While recording, in Insite, monitor the following live data ...

== the engine brake status for stage 1,2,3
== the turbo position commanded
== the turbo position measured.
== Boost level.
== Exhaust pressure level.
== fuel pedal position.

.. then flash the clean factory programming back in it temporarily and do the same recording and same test drive to see if the engine brake and turbo are acting similar.

https://youtu.be/uXL-e4l_nak?is=VpGu7_5CW8Q0ens7
https://youtu.be/CLJzQmlts-s?is=Mippv-fh9FlLaai6
these are both on the demandate tune i will try stock when i get a chance. i dont see anything wrong

[Rawze]

looks pretty good. turbo etc. looks like they are doing their thing properly.

make sure there are no intake, egr, or exhaust leaks in the system.

make sure any block plates are in place properly and are not leaky.

make sure you don't have any leaky injectors too.
leak test: https://rawze.com/forums/showthread.php?...3#pid75483

[tree98]

the L9 engine brake (stock or demandated) is worse than a joke, it isn't even worth having.

[jaysoto]

(08-16-2026 )tree98 Wrote:  the L9 engine brake (stock or demandated) is worse than a joke, it isn't even worth having.

This one doesn't have Jake's I've seen them with Jake's but I'm not sure if it's worth it. Some guys say even with Jake's they don't engine brake very good. The exhaust brake on this one works really good at like 1300 ish rpm anything above that and it doesn't hardly do anything sometimes I turn the switch on and off on decel just to see if I can feel a difference

[DVT873]

These "potato in the tailpipe" engine brakes are pretty useless with manual transmissions. With Allison automatics they are pretty good. The brake drops the RPM a bit which makes the transmission downshift. The trans is actually doing the braking. I first saw these on the Nissan UD trucks back in the late 80's. All manual trans. That brake was standard equipment. They did very little. Maybe on a steep grade? There had to be a reason they were standard.
Jump to the late 90's and they became an option on International with the DT engines. Road testing a tandem with an Allison and a new garbage packer I tried it. I was surprised. At about 50 MPH it slowed quick enough to push me aginst the shoulder belt.

[hookliftpete]

Running an L9 with this setup was similar, if I really needed Id manually engage the fan, which helped a bit.