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Discussion and questions related to the course Practical Standalone Tuning
ive got a RB25DET fitted with a link ecu that was tuned by a local tuner. long story short i was unhappy with the fuel economy joined HPA and have started learning how to tune it turns out at cruize and low engine speeds the vehicle was running very rich ive corrected this now and believe this was due to the tuner fitting the o2 sensor to a pipe in the tail pipe and getting false readings,
anyway the problem im having is that the ecu seems to pick up engine noise above the knock threshold (please see attatched images) i am using audio knock detection (link knockblock) and i cant hear any but afraid that i may be wrong as im inexperienced
ive also removed 6 degrees of timing and this doesent seem to make any difference to ECU detecting knock nor any difference to what i can
can anyone advise on how i should proceed? is it knocking or am i getting false knock? also the engine is fitted with the OE sensors?
I'm can't hear knock in your audio, and the OE sensors are not very good. They're using only one wire and are not grounded to sensor grounds which make the signal pretty bad/noisy. I usually upgrade to a newer Bosch donut sensor and connect the 2nd pin to sensor ground.
The large spike in knock level you see at the right-hand end of both pictures is after you have lifted off, i.e torque has just been reversed. This is very common and I see it on nearly every road car engine. I have noticed I see it much less with proper race engines. So I dont know specifically where it comes from, but possibly something like the sprung clutch plate centre suddenly reversing and bottoming out, or possibly piston slap due to the sudden loss of combustion pressure, or some other drivetrain backlash I haven't considered.
If your ECU is a G4+ then use the "TP Low Lockout" so it disables knock below say 50% throttle to mask this overrun noise. If it is a G4X then you have a few more options to disable under overrun conditions.
The smaller spike you see around the 0:39 second mark in the original timing log is potentially knock or just unoptimised windowing and frequency settings meaning it is intermittently picking up some mechanical noise.
Cheers Frank, I think I'll upgrade them do I need to get 2? Since the OE did or will morning one in the middle suffice?
Adam rodger that I see what you mean by noise after I have lifted off, it's a G4+ so ill configure the low lockout. I'll find out more about setting up the knock control strategy and try to retune them after fitting new sensors
I believe that you are correct with it being related to the sprung center unloading. I had the same noise spikes on liftoff that then disappeared when the clutch was changed to a solid center, with no other mechanical or tuning changes.