MoTeC Global Forum

Hello Everyone,

I've been following the forums for some time, and have also used many of the webinars - which have been great. I'm currently having a problem with my car misfiring badly (almost feels like a commanded torque cut/rev limiter) at 3k rpms and moderate load (does not occur with manifold pressure less than ~110kpa. The car runs well at all other loads/rpm ranges. Any time the car is loaded to greater than ~110kpa and approaches 3k rpms it misfires severely. If revved beyond 3k at low load and then loaded the car also runs fine at higher RPM and on boost. Details on the engine setup are below.

I'm a Motec amateur, but have been through the ECU map extensively and can find no reason that the car would be commanding a torque cut at that range, and it does not appear to be cutting fuel or timing in my logs. The ECU also does not report a ref/sync error that I've noticed. I've played with the timing and fueling a bit, but adjustments in either direction do not meaningfully affect the misfire. I've attached a screenshot of my ref/sync capture recently - I'm new to this process, and am curious if the juxtaposition of the ref and sync waves in this screenshot could cause the phenomenon I'm experiencing. If so, how could I correct it via the software.

To help exclude a hardware issue with the engine/sensors, I was able to swap back in my old Link ECU and the car runs fine with no issues.

Any input or trouble shooting ideas would be greatly appreciated regarding the misfire issue. Also, the lambda 2 sensor won't seem to work. Gives LC-5 error after "counting down" through other LC codes. I've double checked the lambda2 harness for continuity, correct pinout and have tested 3 different LSU4.9 sensors. I can't find any other areas in the map that would prevent lambda 2 from working correctly. Could the ECU itself be faulty?


Ref/sync screenshot:


ECU map and a recent log are attached. Please don't read too much into the current fuel/timing maps - this is just a start file, and the car still needs to be properly tuned once this misfire is sorted.

Engine specs:
-2003 USDM WRX sensors, heads and block, timing gear, etc (very similar to V7 JDM and AuDM STI as I understand it (from sensor perspective, but without AVCS)

- 550cc/min injectors (JDM STI pink equivalent)
- race fuel
- Mag sync and ref sensors
- race fuel
- 10.5:1 compression
- Motec M800 PnP ECU for WRX78

It looks like you my have a problem with the position of the Sync Sensor in relation to the Ref. By design from the factory the ref and sync edges are very close to one another. Head or block machining or aftermarket timing belts and pulleys can cause this issue. This means that at a certain speed the Ref and Sync trigger points cross each other and the ECU identifies this as missed ref teeth. This can be seen by the errors in your log file.

This would be easy to sort out by fitting a Hall sensor instead of the standard magnetic one but you can try setting the Sync sensor edge polarity to "Rise" and the Sync Sensor Trigger Voltage to something like 0.6. This is done under Sensor Setup/Ref Sync Setup/Setup in ECU Manager.

This is not an ideal fix but it may well work or at least confirm that this is where your problem lies.

Thank you for the input. I was considering trying each of those, but was hoping for confirmation from someone with more experience (such as yourself).

I'll give that a shot.
Thank you!