A 2008 Mazda 3 entered the shop with the driver complaining of it running rough after cold starts, and a MIL illuminated. The only DTC stored was P0300 "Random misfire detected."
The vehicle had been in another shop recently, but had left there running in good condition.
What would you recommend doing next, given the data bullet points in last month’s challenge?
Given this information, what would you do next?
- Replace sparkplugs and/or COPs
- Inspect timing components
- Evaluate fuel delivery system
- Decarbonize induction system
For those of you who chose answer No. 3, congratulations!The gas concentration indicated on the analyzer showed that when additional vaporized/atomized fuel was introduced to the induction system, the engine’s combustion was closer to stoichiometry. This points directly at a fuel starvation issue and justifies investing more time evaluating the fuel delivery system.
Answer No. 1 would be incorrect as poor performing ignition components would reflect differently in the gas analysis results. Although the gases would show improper combustion, the Lambda values would still reflect close to stoichiometry.
Answer No. 2 would be incorrect as symptoms exhibited by a cam timing issue would not be corrected with the introduction of propane to the induction system.
Answer No. 4 would be incorrect. Although carbon deposits creating a driveability fault during cold idle conditions can absorb fuel/cause a lean density misfire, the fuel absorbed in the carbon tends to evaporate and overly-enrich the cylinder charge during deceleration.
