What causes fuel trim issues?
Plugged injectors, fuel filters and weak pumps can cause a lot of fuel trim issues. If the code shows a rich condition, over-fueling could be causing the engine to get more fuel than prescribed. Leaking canister purge valves, lack of maintenance, and contaminated engine oil are all potential issues.
What would cause a negative fuel trim reading?
Negative fuel trim values If the displayed fuel trim value is a negative number, it means that the ECU is decreasing the injector pulse width to subtract fuel from the air/fuel mixture to lean out the air/fuel mixture because the input data it is receiving tells it that the mixture is too rich.
How will low volume affect fuel trim?
Low Fuel Volume Much like a vacuum leak, fuel trim corrections will vary with engine conditions. But as RPM and engine load increase, so does fuel demand. The increased fuel demand requires the PCM to provide more correction, and total fuel trim numbers increase with RPM.
What does it mean when your fuel trim is negative?
Rich codes and the drivability issues that accompany a rich running condition would be reflected with negative fuel trim numbers: an indication the PCM is subtracting fuel. Leaking injectors, broken fuel pressure diagrams, improper fuel pressure and skewed sensor readings are a few examples of issues that could result in a rich running condition.
How does a short term fuel trim occur?
Short-term fuel trims occur as a direct result of changes in the oxygen content of the exhaust stream. The exhaust stream is monitored by an oxygen sensor upstream of the catalytic converter, and the signal voltage it generates is directly proportional to the oxygen content of the exhaust stream.
How do you baseline the fuel trim data?
Baselining the fuel trim data is a simple four-step diagnostic process: 1. Connect an OBD II generic scan tool, preferably with recording capabilities. 2. Monitor and record the fuel trim values in the four common operating ranges—idle speed, light load (20 to 30 mph), moderate load (40 to 50 mph) and heavy load (60 to 70 mph). 3.
What causes a fuel trim malfunction in a Mercedes?
Potential causes include a vacuum leak, unmetered air leaks Fuel saturated engine oil Leak in turbo air charge hoses (if equipped) Possibly bad O2 sensor (If Mercedes, may require adaptation with M-Benz compatible scan tool.) Oil contamination in MAF connector or O2 sensor connectors.