ISL 400 overboost problem

[J & Di Cooper]

Have a problem and looking for suggestions.

2005 Windsor ISL 400 with 80k miles.

Recent trip in Blue Ridge mins of Va while using the engine brake (low setting) my Check Engine light came on,  gauge scan showed boost of over 30??!!  Clicked off the engine brake and the light went out and the boost drops back towards 10psi.  Now i'm really paying attention to the dials, as i didn't think there should be boost while using the EB.  All other indicators looked normal.  On the next uphill I see the boost continues to climb around the dial past 0 and at least back to the 10psi mark within a very short distance, at which point I back off the pedal.  I notice the Aladdin % of load gets to about 90%, (normal 90% load equals about 30-34psi boost).  I don't use the EB anymore and keep a close eye on the boost gauge and % of load.  By keeping the load to about 40% I could limit the boost to 30psi by modulating the pedal pressure going uphill.  Engine did not make any strange noises and there was no smoke of any color at any time.  One other note,  for the last couple thousand miles I've noticed a slight whistle sound comes from the exhaust pipe when first started,  as my normal process is to start engine, go to fast idle while building air pressure, stow the shore power cord, do the final walk around and start driving.  I do not know if the whistle is related.  I have checked for loose/frayed/broken wires around the turbo.  I searched here and the IRV site for turbo issues, however most articles deal with loss of pressure and/or ISM-ISX engines which have a different turbo & actuator.

Thanks for your inputs.
John

 

[timaz996]

Even up to 38 psi won't hurt your engine. What is your normal boost?

[Bliksem]

I am suspecting a faulty gauge or sending unit if the engine was running normally. 

 

[96 EVO]

Why would the turbo be producing boost when your off the throttle with the engine brake on 🤔?

[Larry Laursen]

The turbo still provides boost to the intake on a compression release braking system (Jake Brake) which is on the Windsor.  The air is further compressed by the piston which supplies the braking force.  The exhaust valve releases the pressure before the downward stroke thus, not adding any power back to the engine.  As long as your engine RPM is up the turbo will compress the intake air and show on the boost gauge.  

On coaches with an exhaust brake in the exhaust manifold the brake closes the exhaust to create the braking action.  Thus, on an exhaust brake equipped engine the boost will go down when the brake is activated.

The engine computer should have everything under control and there is little need to override it.  

[J & Di Cooper]

Time,  I normally see mid-30's on my dash boost gauge when the Aladdin reads 80-90% load and/or even up to 100% load, although I do avoid pushing the 100% load for any length of time, i.e. long mountain grades.  I'm not in that much of a hurry.

Bllksem,  agreed that is a point to ponder.  Except i do get the "check engine" light whenever the EB is switched on, and it goes out immediately when i switch the EB off.  I did suspect the gauge when i first saw it wound around past the 0 back up towards 10-15 on the next hill,  it's just never exceeded 35 psi before. 

96EVO,  that's my question/concern also.  I don't recall ever really noticing the boost pressure climbing much when using the engine brake for defending grades or just slowing as needed.  

At this point i'm taking it to the local fleet service cummins shop for their review.  I will report back to the group with the results.

Thanks to all for your inputs, hope to see some of you at the Gathering in Tampa.

Choose to enjoy this day.

John