I’m encountering a perplexing issue with a 2015 Gmc Yukon. It’s throwing a Check Engine Light (CEL) and exhibits a prolonged crank time upon starting, although it consistently starts and drives without any noticeable performance problems afterward. Crucially, this Yukon recently had a brand new 6.2L engine installed by Jasper Engines, approximately 400 miles ago. This replacement engine from Jasper came with an Active Fuel Management (AFM) delete, accompanied by a TDN tuner and a pre-loaded tune designed to accommodate the AFM removal. The original engine failure was attributed to a failed AFM lifter, which unfortunately damaged a camshaft lobe and introduced significant metal debris throughout the engine, necessitating the complete engine replacement. Post-installation, for the initial 400 miles, the vehicle operated flawlessly until this CEL and long crank issue suddenly arose.
My primary diagnostic focus has been on the camshaft position sensor system. Observing live data, the camshaft active counts PID (Parameter Identification) is almost consistently registering zero counts. On rare occasions, it might register a very minimal count, perhaps just a few, but the crankshaft active counts are functioning and registering normally. Suspecting a sensor issue, I utilized a Picoscope 4425A to analyze the camshaft sensor waveform. Initially, I observed some minor clipping at the peaks of certain teeth within the waveform. Based on this, I proceeded to replace the camshaft position sensor.
Upon installing a new sensor, the waveform clipping issue was resolved, and the signal appeared clean. However, frustratingly, the long crank symptom and the persistent camshaft-related diagnostic codes remain unchanged.
To further investigate the timing synchronization, I performed a cam/crank sync test using the oscilloscope. The resulting waveform pattern closely matched known good waveforms from other vehicles and examples documented in online forums. Unfortunately, I don’t have the waveform capture readily available on this computer as I’m currently away from the shop for the holiday. However, I’ve included a picture above illustrating the waveform clipping observed on the original sensor before its replacement. At this point, I’m uncertain whether the camshaft code itself could be inhibiting the active counts in the live data, or if this is indicative of a more fundamental issue with the Engine Control Module (ECM) or potentially a consequence of the aftermarket tune installed with the Jasper engine.
Accessing the original tune to revert to stock programming is proving difficult. The technician who performed the engine installation is unable to locate the TDN tuner device. He believes it may have been discarded after a few weeks or possibly left in the customer’s vehicle, and the customer also does not have the tuner. While I have access to OEM GM programming software and could potentially force flash the ECM back to the factory calibration, this would necessitate repurchasing a tuner to re-upload the AFM delete tune, which is not ideal at this stage of diagnosis.
I’m currently seeking further direction on what other diagnostic steps to pursue before considering replacing the ECM. All power supplies, grounds, bus communication signals, and input/output circuits to and from the camshaft position sensor have been meticulously checked at the ECM connectors using back probes while the fault condition is present, and all readings are within specification. In addition to the camshaft position sensor, I’ve also preemptively replaced the camshaft actuator magnet (the large three-bolt solenoid for timing control with a two-wire connector) with genuine OEM GM parts, as per Jasper’s recommendations. Despite these parts testing within normal parameters, Jasper suggested replacement, followed by potential camshaft gear replacement, or even offering a complete engine assembly under warranty if I was uncomfortable proceeding with gear replacement.
Before committing to an ECM replacement, which is both costly and time-consuming, or purchasing a new tuner simply to rule out the aftermarket tune, I am reaching out to the community for any insights or suggestions. Specifically, I’m interested in hearing from anyone with experience with these AFM-deleted Jasper engines and the associated tune software. Is it possible that the tune configuration intentionally disables or disregards camshaft counts within the ECM, and could this be the reason for the camshaft active count PID not functioning as expected? Any guidance or shared experiences with similar scenarios would be greatly appreciated before I proceed further with component replacements.
