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Hi everyone,
I am looking for some feedback on a recent dyno log/graph for a Mercedes C117 CLA 45s running a Stage 2 tune.
Looking at the Dynojet graph (specifically the Air/Fuel Ratio plot at the bottom), it appears the car is running quite lean at the very beginning of the WOT run (from roughly 1,800 RPM up to 4000RPM) before it finally drops and transitions into a richer mixture toward the end of the pull.
My understanding is that while the ECU targets stoichiometric values (14.7 AFR on pump gas) during closed-loop and low-load cruising, a WOT pull should trigger a rapid transition into power enrichment.
I would love to get your insights on a few things:
1. Is this initial lean behavior normal behavior for this platform? Could it be a result of delayed lambda sensor response time on the dyno equipment, or is it a genuine lean condition during the transient transition from closed-loop to open-loop/power enrichment?
2. What maps should I look at to fix this? If it is a real engine condition, should I be adjusting the transient fueling (acceleration enrichment), decreasing the delay timers for power enrichment entry, or modifying the target lambda table at those lower RPM/high-load cells?
3. Safety concerns: At what point does a brief lean spike like this during spool-up become dangerous for a modern direct-injected turbocharged engine?
Thanks in advance for the help!
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