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420whp built KA-T on MS2PNP. Need help figuring why car is breaking up. AFR darting back and forth

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Hello there,

Looking for help and ideas with my breakup issue here. The car ran normally before on the same ignition setup. Unsure when or what caused the change.

I’ve attached a link with tooth logs, composite, and other logs. The logs were taken at a steady throttle input 2000rpm.


Setup: KA24DET on MS2PNP with COP wasted spark. Please let me know what details you need to know. Compression came out good.

Attached Files

The AFR issue may simply be a result of the ignition mis-fire, and not otherwise relevant - but a check over the fuelling side, especially electrical connectors, would be wise.

From what you say, it seems you made no changes, not even a 'tune up'?

If so, did it suddenly happen, or did it develop over time? Is there a difference with different rpm and throttle ranges?

You don't mention the spark plugs, have you pulled them to check what they look like? They can tell a lot about what's happening in the engine.

What is holding those COPs onto the plugs? Are you sure they are making good contact? Check each coil connector for broken wires / bad crimps (give them a good pull test).

I would get a spare COP, and swap it one at a time to isolate a bad COP unit.

I agree with Gord, any lean-spikes in lambda can be a result of misfires, not necessarily an indicator of a fuel tuning problem. But give the injector wires a pull test as well to make sure they aren't compromised.

i have just chased a similar issue on a sr20 engine with a r35 coil on plug conversion, I found the kit didn't allow the springs inside the boot to the sparkplug

and even when I cut down the boots to make this contact the engine misfired still and was cured by refitting the factory r35 boot and not running the adaptor plate that holds the coils down, this is just an example of issues we come across from time to time in tuning, I agree with with the above comments by David and Gord.

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