The journey to optimal car performance can sometimes lead down unexpected paths, especially when modifications are involved. Recently, we encountered a perplexing issue with a vehicle that returned to our shop after some aftermarket enhancements. The initial setup involved modifications to the wastegate and air connections, hinting at a pursuit of increased power. However, the car presented a new set of challenges that pointed towards the Mass Air Flow (MAF) sensor and the dreaded P0104 Code.
Initially, the modifications seemed to have unintended consequences. The car was experiencing issues where it was blowing air into the crank vent under boost and drawing unmeasured air during normal driving conditions. After addressing these immediate concerns, the car showed improvement, achieving 9 psi of boost compared to the previous 5 psi. Despite this progress, the MAF history indicated ongoing problems.
The MAF sensor readings were erratic, displaying chaotic mass values rather than stable voltage readings. This translated to noticeable drivability issues; the car hesitated and felt like it was constantly “thinking” before responding. Diagnostic logs using SCT further confirmed the MAF sensor as the culprit, revealing chaotic readings that correlated with injector pulse irregularities. A thorough electrical inspection and even a MAF sensor replacement failed to resolve the problem, suggesting a deeper, systemic issue. Interestingly, the car seemed to be pulling timing when these MAF reading anomalies occurred, further impacting performance.
Suspicion then fell upon the intake design. The installed intake was identified as a copy of the Turbonetics kit, marketed under the name BoostBrothers, and included a honeycomb element positioned before the MAF sensor. To test this hypothesis, all turbo-related components were disconnected, and a JLT 110 intake was installed. The transformation was immediate and significant. The car began to run smoothly, and the MAF errors vanished, even during brief test drives. Logs taken during this configuration revealed a spike in airflow, the cause of which remained unclear, possibly linked to load issues or even the disabled anticipation logic. It’s crucial to note that the voltage readings remained stable, while the calculated air mass was fluctuating.
Further testing, maintaining the JLT intake but with the turbo still disconnected, reinforced the diagnosis. No MAF errors were detected, and the engine ran richer (10.2 AFR compared to 11.7 AFR with the turbo connected). This solidified the suspicion that the intake design was indeed the root cause, improperly influencing MAF sensor readings. With the JLT intake, MAF and spark curves, along with injector timings, were smooth and consistent. In a final diagnostic step, the honeycomb element was removed from the suspect intake and reinstalled. This immediately exacerbated the problem. The car became undrivable, triggering the p0104 code – Mass Air Flow Circuit Intermittent – within seconds of starting.
The culmination of these tests pointed unequivocally towards the intake design as the source of the p0104 code and related MAF sensor issues. The evidence strongly suggests that the airflow dynamics within the BoostBrothers intake, particularly with the honeycomb and its configuration, were disrupting the MAF sensor’s ability to accurately measure airflow. The proposed solution is to transition to a draw-through MAF setup. This approach, where the MAF sensor is positioned downstream of the turbo, is expected to rectify the airflow measurement issues and eliminate the p0104 code, ultimately restoring optimal and reliable engine performance.
