Cadillac XT4 Diesel Power Loss and Fuel Issues

After seeing similar symptoms on my 2018 Cadillac CT6 diesel, it turned out the fuel injectors were failing, which caused a chain of issues. Low power and high consumption often point to fuel delivery problems. In my case, faulty injectors led to uneven cylinder pressure and eventually damaged the intake manifold from irregular combustion. The repair required replacing all fuel injectors because running with bad ones had created carbon buildup in the cylinders. This isnt just a minor fix, when fuel injectors malfunction, they can cause engine knocking and potential damage to other components. Your symptoms match closely with what I experienced, especially the cylinder pressure readings being off. While you mentioned the timing belt is new, these symptoms typically point to fuel system issues rather than timing problems. Based on the high mileage and symptoms, getting a proper fuel system diagnosis should be priority. Ignoring fuel injector problems can lead to more severe engine damage, particularly in diesel engines where injection pressure is critical for proper combustion.

Thanks for detailing your injector problems. Had almost identical issues with my XT4 last winter, and my spark plugs were actually fine despite similar symptoms. The root cause turned out to be worn piston rings causing low compression, the diagnosis initially pointed to fuel delivery like yours. Would you mind sharing what the total repair cost was for your injector replacement? My piston ring job was quite expensive and Im curious how it compares. Also wondering if youve had any other issues pop up since the repair? My engine has been running much smoother after fixing the rings, but Ive noticed the turbocharger seems a bit sluggish now.

Happy to report my fuel injector repairs were fully covered under warranty since it was traced back to a previous incomplete repair job. The mechanic confirmed the cylinder pressure fluctuation was completely resolved after addressing the underlying issue. The diagnostics showed the intake manifold pressure is now steady and engine knocking has completely disappeared. The engine has been running flawlessly for the past 8 months, no sluggish turbo response or other issues. The fuel economy is back to normal and power delivery is smooth across all RPM ranges. The key was catching it early before the faulty injectors could cause more extensive engine damage. Your turbo sluggishness might be worth checking out though. Sometimes when fixing one issue like piston rings, it can reveal wear in other components that was previously masked by the original problem. A proper diagnosis would help rule out any connection to the previous repair work.

Thanks everyone for the input. Finally got my XT4 properly diagnosed and fixed last week. Spent 4800€ at an independent shop after getting quoted nearly double at the dealership. The worn piston rings were causing oil to leak into the combustion chamber, explaining the low compression and power issues. The mechanic found some scoring on the cylinder walls but nothing severe enough to require a full rebuild. They replaced the piston rings, cleaned the intake manifold, and did a full system inspection. The sluggish turbocharger response turned out to be from oil contamination, which they cleaned up during the service. Engine is running strong now, compression is back to spec, fuel economy improved dramatically, and the check engine light has stayed off. Learned my lesson about addressing these issues quickly before they cause more damage. The fuel injectors and spark plugs checked out fine, so at least those expensive parts didnt need replacing.