Mitsubishi GTO trigger error

[MGV101]

I suddenly started getting trigger errors while upping the boost on a Mitsubishi GTO. It would happen at any rpm once boost rises above ~0.9 bar and would happen in around 1/3 of my ramp runs. It seems to be ok after I dialled down the boost again.

I discarded most but two of my logs that had the trigger errors as there were way too many logs to save while at the dyno. As I returned home and started reviewing them, in one of log I noted something strange. Right before the trigger error, Trigger 1 Status showed "Test Gap" where normally Trigger 1 Status would only show "Count Large" and "Count Small".

The crank trigger on a GTO is just has three large teeth and gaps with no missing teeth. Count Small is just referring to the higher teeth on the wheel after the falling edge is detected while Count Large is referring to the lower gaps in between as the rising edge is detected. 

I don't get such strange findings in my other logged run with trigger error but my logging rate was definitely not high enough to catch all trigger state so it might have still been present but the log just missed it.

Why would the ECU suddenly be looking for a gap all of a sudden?? (The terms may be confusing here I assume the gap here is referring to the missing teeth and not the regular gaps between the teeth) Did that unusual behaviour of the ECU cause the trigger or did the trigger error cause this behaviour?

Also another strange thing was, after the trigger error, the engine started to run extremely rough. This did not occur during other trigger errors (and this is probably why I had this log saved and not the others). However, after stopping the engine twice and restarting the ECU again everything was back to normal.

Attached is a trigger scope take at ~3000 rpm on boost at steady state and also the aforementioned log. Screen shots also attached.

There is also some noise in the trigger scope but is it sufficient to case a trigger error? 

trigg 3000.llgx trig stut.llgx

[Adamw]

After the ecu has achieved sync and the engine is running you should only see states count small/count large.  "Test Gap" is possibly a confusing term but this state means the ecu is looking for the unique event that identifies TDC.  

So, seeing this state during running means the ecu has received an edge where it is not expected, it has lost position.  It cuts all fuel and spark, sets RPM to zero and trigger state starts back at "Idle" for a complete re-sync.  To re-sync the full range of states will be stepped through; Idle>Blank Teeth>First Tooth>Second Tooth>Test Gap>Start Counting>Count Large>Count Small.   Just due to the logging rate you are only seeing the "test gap".  

The fact it is occurring at high load would suggest ignition noise is getting into the trigger signal and sometimes a spike is large enough and long enough to be considered a valid edge.  Spark voltage increases with cylinder pressure, so more boost means more potential for high voltage noise, and coil current increases with dwell, voltage and RPM, so there is also more potential for current to cause noise or offsets as well.     

Does it still have a stock ignition system?  Make sure spark plugs are resistor type and are in good condition, reduce gap if it is not already too small, ensure good quality resisted HT leads, make sure the ignitor(s) ground is good.  Im not sure about the GTO, but if similar to the early Evo coils they had an internal noise suppression capacitor that grounded through the mount so this needs to be good contact also.  The internal capacitor can die of old age also.   

 

 

[MGV101]

Thank you for the detailed reply Adam.

The ignition system is still stock. Looks like the coils had been recently replaced as they looked almost new (trying to confirm whether these are genuine stock coils now). Plugs are your typical IK22 spark plugs used in most JDM engines so they are definitely resistive type spark plug. The plugs were new but we measured a few of them just in case anyway and they all measured find at 3.XK ohm (don't remember the exact resistance).

Ignition leads were new and came from here:
https://mrretroleads.co.uk/product/lime-green-8mm-performance-ignition-lead-kit-zetec-black-top-kit-car-part-built/

There was no marking/branding on these "custom" leads but we measured the resistance and after factoring in the length, it does come close to the website's spec of 5.6Kohm per meter .

Lastly, yes there was a capacitor near the coil just like the early Evos. The condition looked ok with minor weathering. We tested the capacitance and measured 460nF which was close enough to the 0.5uF marked on the capacitor casing itself.

Without any other obvious faults/source of EMI, we are now gapping down the spark plugs from 0.8mm to 0.6mm and hope that would help. But yes I still agree the noise is most likely from the ignition system. Maybe there are damage to the stock signal wiring/shielding/grounding that is amplifying the noise. The car was in a very sorry/neglected state when it first came in.

It's no longer on the dyno so it is difficult to consistently test for the trigger error again to confirm whether gapping down the spark plug have solved it. Only time will tell.

 

[MGV101]

Further update...

After gapping down the plugs (from ~0.75mm to 0.6mm), we did a short drive and was still getting trigger errors on boost.

Just noted the dwell time on the coils were set to ~5-6ms on the base map which seemed a little high. Have lowered it down to 4.5ms and lets hope that would help.