2007 Western Star 4900 - Series 60 Detroit - Low Boost and High EGT

Question

My 07 Western Star is feeling sluggish. Usually, I can hit 32-35 PSI of boost under load, but now it struggles to get past 20 PSI. At the same time, my EGT gauge is climbing much faster than it used to. No active codes.

I don't hear any obvious whistling from the CAC or boots. I'm thinking either the VNT turbo is acting up or maybe a fuel restriction? The Turbo was replaced about 100k miles ago.

OwnerOpOlly · Answer

Check your intake manifold pressure sensor (boost sensor). If it's dirty or failing, the ECM won't fuel the engine properly because it doesn't think there is air, even if the turbo is spinning.

EmissionsEric · Answer

✅ Confirmed fix: The Variable Nozzle Turbo (VNT) actuator linkage had become stiff. It wasn't completely stuck (so no code), but it wouldn't fully close the vanes to building boost quickly. I used high-temp anti-seize on the pivot points and worked it manually with a pry bar until it moved freely. Boost is back to 34 PSI.

2007 Western Star 4900 - Series 60 Detroit - Low Boost and High EGT

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