2016 Mack Pinnacle MP8 - Excessive Regen Cycles and SPN 3251 FMI 0

Question

My Mack is driving me crazy. It's asking for a parked regen almost every day now. I've been getting SPN 3251 (High DPF Differential Pressure). I've pulled the DPF and had it cleaned and baked at a local shop, but two weeks later the soot levels are back up in the red.

The truck has 650k miles. I don't see any black smoke, but clearly the engine is loading the filter way too fast. Turbo seems to be boosting fine and I don't have any boost leak codes.

DieselDan_77 · Accepted Answer

✅ Confirmed fix: You need to check your 7th injector (Hydrocarbon Injector). On the MP8, if the 7th injector is 'dripping' or has a poor spray pattern, it won't atomize the fuel correctly during the regen, leading to incomplete burns and rapid face-plugging of the DPF.

I replaced the HC injector and the fuel line going to it. The old one was completely carboned over. After replacement and a forced service regen to reset the soot map, the truck is back to normal regen intervals (about every 25-30 hours).

Ms_Torque · Answer

Look at your intake throttle valve. If it's sticking partially closed, you'll get a rich condition that generates excess soot without necessarily throwing a code for the valve itself. Also, check your CAC for tiny leaks.

2016 Mack Pinnacle MP8 - Excessive Regen Cycles and SPN 3251 FMI 0

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