Embarking on a car modification project, especially an engine swap, is a thrilling endeavor for any automotive enthusiast. Like many, the allure of upgrading my Mitsubishi Lancer led me down the path of replacing the original 1.5L engine with a more powerful 1.8L 4G93. This journey, while rewarding, wasn’t without its challenges, particularly when it came to diagnosing post-swap issues using OBD2 diagnostics. Let me share my experience, focusing on troubleshooting common problems that arise after a 4G93 engine swap and how OBD2 systems play a crucial role in pinpointing these issues.
My original ride was a 1999 Lancer GLXI Coupe, sporting a modest 4G15 1.5l 12V engine. Seeking more power, I acquired a 2002 Lancer MR Coupe donor car equipped with a rebuilt 4G93 1.8l 16V engine. The 4G93, with its coil pack ignition and seven-bolt configuration, promised a significant performance boost over the older 4G15. The swap itself involved meticulous work, from sourcing compatible parts to painstakingly matching wiring looms. I’m no stranger to car maintenance, having always handled repairs and upgrades myself. This project was a deep dive, requiring careful attention to detail at every stage.
The engine rebuild and swap process included a comprehensive list of quality components: JUN valve stem seals, Hastings piston rings, JUN bearings, NOK seals, NGK iridium plugs, Gates timing belt kit, Exedy heavy-duty clutch, and more. Beyond just bolting parts together, I focused on precision, measuring clearances with PlastiGauge, resurfacing mating surfaces, porting and gasket matching the head and manifolds, and meticulously cleaning and inspecting every component. The electrical aspect was particularly demanding, requiring me to dissect and merge wiring looms, bypass the automatic transmission ECU from the donor car’s harness, and even reprogram the ECU to recognize my original key. The aim was a factory-level finish and reliability, and for the most part, I achieved that.
However, after the swap, some gremlins emerged, hinting at underlying issues that needed attention. These weren’t catastrophic failures, but rather symptoms suggesting the engine wasn’t running optimally:
- Rich Running: The engine seemed to be running rich, indicated by a strong fuel smell and likely poor fuel economy.
- Exhaust Popping on Deceleration: During deceleration, noticeable popping sounds emanated from the exhaust manifold, reminiscent of an anti-lag system, but clearly not intended.
- Constant Fuel Pump Operation: With the key in the ignition “ON” position, the fuel pump ran continuously without priming and shutting off as expected.
These symptoms pointed towards potential problems within the fuel delivery system or engine management, areas directly related to the OBD2 system’s diagnostic capabilities.
My initial suspicion revolved around the ECU and fuel delivery. Was the 4G93 ECU from the automatic donor car optimized differently compared to a manual transmission ECU? Could this difference be contributing to the rich running condition? The constant fuel pump operation also suggested an electrical control issue, possibly related to the ECU or fuel pump relay.
To investigate further, I turned to OBD2 diagnostics. Using a universal OBD2 scanner, I checked for Diagnostic Trouble Codes (DTCs), but surprisingly, none were present. While the absence of DTCs might seem reassuring, it doesn’t mean everything is perfect. OBD2 systems are designed to detect major malfunctions, but subtle issues like slightly rich running conditions might not always trigger fault codes, especially if sensors are still within their acceptable operating ranges but not optimal.
Despite the lack of DTCs, the OBD2 scanner’s live data readings offered valuable insights. I examined parameters like:
- Fuel Trims (Short Term and Long Term): These readings indicate how the ECU is adjusting fuel delivery to compensate for deviations from the ideal air-fuel ratio. High positive fuel trim values would suggest a lean condition (ECU adding fuel), while negative values would suggest a rich condition (ECU reducing fuel). In my case, negative fuel trims would likely confirm the rich running suspicion.
- Oxygen Sensor Readings: The O2 sensor(s) measure the oxygen content in the exhaust gas, providing feedback to the ECU for air-fuel ratio control. Analyzing the voltage readings and waveforms of the O2 sensors can reveal if the engine is indeed running rich or lean.
- Mass Air Flow (MAF) Sensor Readings: The MAF sensor measures the amount of air entering the engine. Incorrect MAF readings can lead to inaccurate fuel calculations by the ECU.
- Engine Coolant Temperature (ECT) Sensor Readings: An improperly functioning ECT sensor can cause the ECU to think the engine is cold, leading to over-fueling and rich running.
By carefully analyzing these live data parameters with an OBD2 scanner, I could gain a clearer picture of what was happening within the engine management system and pinpoint the source of the rich running and other symptoms.
One question I pondered was injector compatibility. The original 4G15 engine used smaller 166cc injectors, while the 4G93 likely used larger 210cc injectors. Could the larger injectors from the 4G93, when paired with the ECU, be delivering too much fuel, causing the rich condition? Experimenting with the 4G15 injectors (though not a long-term solution) could be a test to see if it leans out the mixture, providing further clues. However, proper tuning or ECU reflashing would be necessary for a permanent and optimized solution.
The exhaust popping during deceleration could also be related to the rich running condition. Excess fuel in the exhaust system can ignite in the hot exhaust manifold during deceleration, causing the popping sound. Addressing the rich running issue might also resolve the exhaust popping.
Regarding the constant fuel pump operation, this is less likely directly related to the rich running but more indicative of an electrical control or ECU programming issue. It’s possible that the ECU, expecting an automatic transmission setup, is not controlling the fuel pump correctly in my manual transmission swapped car. Further investigation into the wiring and ECU programming related to the fuel pump control circuit is needed.
In conclusion, while the 4G93 engine swap has brought a welcome performance upgrade to my Lancer, the post-swap issues highlight the complexities of engine modifications. OBD2 diagnostics are invaluable tools in troubleshooting these problems. By utilizing an OBD2 scanner to read live data, particularly fuel trims and sensor readings, and by systematically investigating potential causes like ECU mapping, injector size, and fuel pump control, I can effectively diagnose and address the remaining issues, ensuring my 4G93 swap runs optimally and reliably. For anyone undertaking similar engine swaps, understanding OBD2 diagnostics is not just helpful, it’s essential for a successful and trouble-free project.
