Turbo boost dropping on grades

[tom chelbana]

Have an 04 Essex with a 500 ISM engine that has a turbo boost problem on 6% plus grades that on some grades the boost will raise to 30 psi and have good power but many times on the same grade and RPM it will not raise any hire then 23. When the boost is low there is what you would a loss of speed by over 5 mph. You just don't know from one grade to another what your turbo boost will be which then the loss of power. What controls turbo boost is the ECM but why would the boost be so variable? This started about a year ago and the boost was higher around 35 and was the same on all grades.

[Genset]

Two thoughts having the ISM500,
1st Would be double. Checking all the hose clamps on all the tubing from turbo to intake including the CAC for damage/leaking.
2nd Would think the boost sensor is acting up, without proper boost, it does not give full fuel.
My boost will run into the 32-33 psi and hold it there on a hard pull, that might be due to the ECM & the bypass turbo combination,
Was told by Cummins that it would be a very strong 500. It started as a ISM450, but was capable to upgrade to the 500 but using the older turbo bypass setup with the new ECM settings. It does run strong in my 30,000 lb coach.
Dave M

[Genset]

Tom,
One other thought, think you have the VG turbo, they have had issues with the vanes and not making full power. Just a thought, i do not have that model, but have heard some rumblings about the VG turbo.
Good luck
Dave Zm