Idle RPM Dropping Issue - M150 ECU

Hi everyone,

I'm working on a FSAE car using a CBR600RR paired with a M150 ECU. Recently, after installing a new engine utilizing higher compression pistons, we are having an issue with idle in which every 30-35 seconds, the RPMs will drop to a point where the car's ECU has to give it more throttle in order to prevent it from stalling. This is very repeatable and happens like clockwork. I would imagine it's something in the tune's idle parameters that is causing this, but we have not been able to find a solution to fix this. Any ideas? I will provide an I2 file on this post, and would be happy to share the tune if necessary. Any help or guidance would be appreciated!

- Ryan

The engine is stable with the least throttle opening early in the log before fuel trimming comes online and adds a ton of fuel, so perhaps your lambda reading is wrong. If reversion or a leak is getting fresh air in the system that could be causing a false lean condition.

Normally richening an engine from 1.1 lambda to 0.93 lambda would increase torque, requiring less throttle opening to maintain a given idle speed, but that's not the case here.

The first and worst drop occurs where fuel trimming becomes active and adds lots of fuel, up to 47%.

After verifying the sensor is in a position to get a good reading, no leaks are present, sensor is in good shape, then I suggest adjusting the calibration until fuel targets are hit with minimal fuel trimming required. That will stabilize and improve operation in general.

In addition, I'd allow more positive timing correction as part of idle control, so it can assist more when there's a dip.

I can't see the PID settings for idle, but the integral very slowly winds down, then at the same throttle opening and airflow you get the dip, and the system isn't very quick to respond since there's no proportional response, but the I term does wind up as part of saving the engine, then gradually winds back down and repeats.

A sudden load on the engine is another potential cause. I don't know the setup on the car, but if you're running a CVT or a torque converter and it starts to grab, that could also be a factor.