I’m encountering a perplexing issue with a 2015 Gmc Yukon. It’s exhibiting a prolonged crank time and has triggered the Check Engine Light (CEL), yet the engine starts and the vehicle demonstrates no noticeable drivability problems. This particular 2015 GMC Yukon recently underwent an engine replacement, approximately 400 miles ago, with a new 6.2L engine sourced from Jasper Engines. Crucially, this engine was installed with an Active Fuel Management (AFM) delete, facilitated by a TDN tuner and a preloaded tune designed to bypass the AFM system. The original engine failure stemmed from a collapsed AFM lifter, resulting in camshaft lobe damage and significant metallic debris throughout the engine. Following the engine replacement, the 2015 GMC Yukon operated without incident until recently, when the CEL illuminated, accompanied by the long crank symptom, but no other performance issues reported by the customer.
My primary observation during diagnostics is the inconsistent behavior of the camshaft active counts live data PID. It almost consistently registers zero counts. Occasionally, it might flicker and register a minimal count, perhaps one or two dozen, but this is infrequent. In contrast, the crankshaft active counts register as expected and appear normal. Suspecting a potential issue with the camshaft position sensor, I utilized a Picoscope 4425A to analyze the sensor waveform. Initially, the waveform displayed evidence of clipping at the peaks of some teeth. Based on this, I proceeded to replace the camshaft position sensor. Post-replacement, the clipping in the waveform disappeared, but the long crank issue and persistent camshaft-related codes remain.
To further investigate, I performed a cam/crank synchronization test using the oscilloscope. The resulting waveform aligned with known good waveforms from comparable vehicles and examples documented in online resources. Unfortunately, I don’t have the waveform readily available on this computer as I am currently at home. However, I have included a picture above illustrating the waveform clipping observed on the original sensor prior to its replacement. I am now uncertain if the persistent camshaft code is inhibiting the active counts in the live data, or if the root cause lies within the ECM or potentially the custom tune implemented with the new engine.
Accessing and reverting the tune is proving difficult, as the technician responsible for the installation has misplaced the TDN tuner. He believes it was either discarded or inadvertently left in the customer’s vehicle, and the customer also cannot locate it. While I have access to OEM GM programming software and could potentially force flash the ECM back to the factory stock calibration, this would necessitate purchasing a new tuner to reinstall the AFM delete tune, which is not ideal at this stage.
I am currently seeking guidance on further diagnostic steps before considering more drastic measures like flashing the ECM or replacing it outright. All power, ground, bus signal, and input/output circuits to and from the camshaft sensor have been meticulously checked at the ECM connectors using piercing probes while the issue is present, and all readings are within specification. Furthermore, preemptively, I have already replaced both the camshaft position sensor and the camshaft actuator magnet (the large three-bolt solenoid controlling timing with a two-wire connector) with genuine OEM GM parts sourced directly from the dealer, as per Jasper Engines’ recommendation. Despite these parts testing within specification, Jasper suggested these replacements before considering more complex interventions like camshaft gear replacement, and even offered to send a complete engine assembly under warranty if necessary, should I be hesitant to replace the gear.
Before proceeding with ECM flashing or replacement, especially given the expense and time involved compared to acquiring a new tuner, I am hoping to leverage the collective expertise of this forum. Specifically, I am interested in hearing from anyone with experience with Jasper Engines’ AFM delete engines and the associated tuning software. Is it possible that the tune itself is configured to disregard camshaft counts, thus causing the camshaft active count PID to be non-functional? Any insights or suggestions on diagnosing this 2015 GMC Yukon issue would be greatly appreciated.
