Dacia 0.9 TCE Engine Problems
The Dacia 0.9 TCe engine, notably a model featured in the Dacia Logan, has gained attention for a specific misfiring issue. Let’s break down the problem and understand its potential solutions.
Background of the Issue
Owners have reported that the Dacia Logan, equipped with the Renault H4B 900cc turbo three-pot engine, has shown exceptional reliability. However, with regular usage, around the 37k miles mark, some have started to notice the car sounding uneven and displaying hesitation when the engine is cold. This is typically observed as a misfire during cold idle which disappears as the engine warms up.
Technical Insights
The misfire appears to be most prominent between 1300-1500RPM under no load. At speeds either below or above this range, the misfire vanishes. When the engine is cold, cylinders 1 and 3 seem to be the most affected, while cylinder 3 dominates the misfire count as the engine warms up. Furthermore, cylinder 3 has shown a roughly 20% increase in accumulated knock detection.
Interestingly, no engine codes, either OBD2 or specific to Renault, have been detected during this malfunction, making it a bit trickier to pinpoint the exact issue.
Initial Troubleshooting Steps
- Spark Plugs: Given the mileage on the car, a natural step was to change the spark plugs. However, this didn’t alleviate the issue.
- Coils: Switching the coils around didn’t result in the misfire shifting to another cylinder. Even after borrowing a known set of functional coils, there was no change, suggesting the problem wasn’t related to ignition.
- Fuel Trim: The fuel trim data in the closed loop at warm idle displayed +4.7% long term and between -8% to -10% short term. This indicates a net reduction in fueling. The oxygen sensor functioned as expected at idle but ceased to work when misfires were detected.
Main Diagnosis and Solution
Given the data, it was hypothesized that the problem might be tied to a fuel delivery issue, specifically concerning injector 3. The injector might have been performing inadequately at low duty cycles pulse widths. Yet, this raised questions since the engine idled smoothly when warm and the expected positive fuel trims weren’t as high as they should be if this was the primary problem.
Ultimately, replacing the injectors with a set from a low-mileage engine rectified the issue. This suggests that there was indeed an inconsistency or malfunction in the original injectors’ performance.
Next Steps
While the replacement of the injectors resolved the immediate concern, it’s still a mystery as to why the original injectors malfunctioned in the manner they did. It is recommended to get the original injectors tested to ascertain the exact nature of the malfunction, which might provide deeper insights into the cause of the issue.
Conclusion
The Dacia 0.9 TCe engine in the Logan model displayed an unusual misfire issue around the 37k miles mark. Though it initially seemed like an ignition-related problem, the solution lay in the fuel injectors. Owners encountering similar symptoms should consider the injectors as a possible point of inspection.