Cummins ISX VGT hunting

[Joesixpack]

Hi, long time no see and forgot what a great resource this is.
We have a 2011 T800 with a ISX and lately the VGT turbo is hunting I'll call it, does an oscillating closing the vanes and boosting up then dropping over and over during light load, it just don't seem right either if you find a happy medium where it isn't oscillating and acts constipated and boosting to hard for the load and not running free.

I did change the MAP sensor and it didn't effect it. I suppose the next up is the VGT controller? It's not throwing any codes but the truck is deleted and who knows what it's letting through.

And of course my Insite isn't working! Been a long time since I needed to plug it in!

[Rawze]

Sounds like a bad/unstable ECM programming to me.

The VGT turbo after a de-mandate, should not be 'hunting' like that at all.

- Back up the ECM image with Caltherm (so that you do not loose it) and send me an e-mail copy of the program to that is can be reviewed.

[alamow]

I had a simular experance and found the exhaust pressure sensore tube was blocked.

[Rawze]

(05-31-2024 )alamow Wrote:  I had a simular experance and found the exhaust pressure sensore tube was blocked.

Checking for a blocked up exhaust sensor circuit is decent advice... however, even with a blocked exhaust sensor, it still should not be 'hunting' like that whatsoever after a proper de-mandate.

The turbo should have been properly re-programmed and the engine operating mode logic changed so that the turbo does not want to spool up to begin with. It should not be hunting for any positions, and any spooling up of the turbo at idle is a sign that the engine is still trying to warm up an aftertreatment can that no longer exists.