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This is a secondary waveform from a 2 cylinder Aprilia motorcycle. It is a 3 wire cop coil. I am not sure what to make of this. Has misfire on that cylinder. Short term fuel trim shows negative 30 on that cylinder. Thoughts. I have included the Primary waveform as well.

Cyl 1 is negative 30, cylinder 2 is positive 30. Checked injectors - fine, disable o2 sensors, cyl 1 trims go near zero, cyl 2 stays at positive 30. No air leaks, only one map sensor which is common to both cylinders, no MAF.

No, also did an in cyl compression test and the intake vacuum on both cylinders if fairly close. I still would like to see an answer for why the secondary looks like that..

I agree on the low resistance, but plug gaps are good and plugs are not fouled. Cyl 2 looks totally normal - see waveform. The secondary voltage is not uncommon from the bikes I have tested. I have included an in cyl comp test on idle for cyl 1, seems normal to me except the intake vacuum is slightly lower than what I'm use to, usually closer to 10psi but it is Fly by Wire so that may make a difference.

I did swap plugs and the cop coils as well. The issue did not move. Really has me stumped.

Misfire on 1 of 2 cylinders - YES

Huge fuel trim imbalance cylinder to cylinder - YES

Swapping the ignition coil and spark plug did not change the issue. - YES

The secondary ignition pattern from the faulty cylinder appears to have substantially lower spark line voltage than the "good" cylinder. - YES



Is the misfire a dead hole or is the issue fault less frequent? - INTERMITTENT, MOSTLY WHEN ENGINE WARM

Does this machine have individual exhaust oxygen sensors? - YES

What is the exhaust system like? - STOCK 2 INTO 1 - LINK PIPE BETWEEN PIPES CLOSE TO EXHAUST PORTS

What kind of fuel system does this machine have? - 2 THROTTLE BODIES LINKED TOGETHER (THEY ARE SYNCED) - FLY BY WIRE CONTROL - SEQUENTIAL INJECTOR FIRING

Does it hold pressure when the machine is off? - YES, TESTED INJECTORS FOR FLOW AND LEAKAGE

If you were to disable fuel trim correction how does the engine run? Unplug the O2 sensor(s). - UNPLUGGED O2 SENSORS. CYL 1 THAT WAS NEGATIVE 30 GOES TO BASICALLY ZERO, CYL 2 THAT WAS PLUS 30 STAYS AT PLUS 30

James H wrote on Oct 2^nd, 2026 at 9:16am:



Were you able to determine where that additional leakage was going?

How are the valve clearances managed on this engine? I'm sure by now you've checked them but we haven't discussed it.

Is your cranking WOT picture using two WPS transducers or is it the combination of two different captures?

One thing that worries me when comparing in-cylinder captures on multi cylinder bikes is the effects of uneven firing strokes. According to the web this on uses a cross plane crank with a 270° firing pattern. This will cause larger crank speed variations which WILL have an effect on cylinder pressures when measured by the WPS.


James H wrote on Oct 2^nd, 2026 at 6:20am:


My purpose with this one was to see how the engine ran on fixed values. By unplugging the O2 sensors the feedback loop for the ECM is broken which SHOULD prevent the fuel trim from changing. I don't know if you would have to clear the learned fuel trim to put the ECM back into a predetermined values.

Have you scoped or otherwise measured the O2 sensors output?

Have you scoped the fuel injectors?

Embarrassed that I missed this but just realized that my cranking compression valve of 160 psi and running compression value are close to the same which obviously isn't right. I originally checked for air leaks and there was none that I could see. I am going to have to look again or for another possibility...