2012 Kenworth T660 Cummins ISX15 - Low Boost and High Exhaust Temps

Question

My 2012 ISX15 is dogging it on hills. I'm barely seeing 22-24 psi of boost when I used to see 35+. At the same time, my pyrometer is climbing way faster than normal, and I'm hearing a high-pitched whistle coming from the passenger side when the turbo tries to spool up.

I've looked for soot marks around the exhaust manifold but everything looks dry. The actuator on the VGT turbo seems to be moving when I first key on, but I'm getting an SPN 641 FMI 7 which points towards a mechanical system not responding. I'm worried the VGT vanes are stuck or the actuator is toast. Has anyone had luck cleaning these or is it a mandatory replacement?

WeldShopWanda · Answer

✅ Confirmed fix: The VGT actuator internal gears were stripped. While the motor was humming, it wasn't actually moving the nozzle ring inside the turbo. I replaced the VGT actuator and used INSITE to perform the calibration procedure. Boost returned to 36 psi and EGTs dropped back to the 900-degree range under load. Make sure the sector gear on the turbo itself moves freely before installing the new actuator.

ChevyChuck · Answer

Check your EGR valve. If it's stuck partially open, you'll lose drive pressure to the turbo, which results in low boost and high EGTs because you're recycling hot exhaust into the intake constantly. Try blanking it off temporarily just to see if your boost returns, but don't leave it that way.

2012 Kenworth T660 Cummins ISX15 - Low Boost and High Exhaust Temps

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