Have and S300. Typically run 18psi on pump. Has been running for a couple years that way. Started breaking up after 12-13psi the other day. Replaced the plugs, same issue.

What can I log or check to diagnose?

-platinum

 

Check that you properly gapped the new plugs.

 

map sensor maybe, like stated check the plugs for proper gap and same brand as previous usage

 

1. Make sure your air fuel ratios are on par.
2. Check plug gap as mentioned before.
3. Consider taking the vehicle back to your tuner for inspection, a good tuner can diagnose an issue such as yours in less then a few minutes....

 

A/F looks solid. 11ish at wot. Idle is spot on 14.7.

New plugs are the same brand and heat range gaped at .028

Nothing I can log on the S300 to determine the issue? I am going to check cap and rotor today.

-platinum

 

No, if it was fine before and is now suddenly doing this, unless it's a bad sensor logging will not help you.

Try gapping lower, honestly.

 

Try .020" see if the problem lessens.

 

I was going to suggest .024

 

also what plugs you use are something to consider too. my bkr7e's started breaking up one night at the track and that was on 11 lbs. i had them gapped to 28. now i gap mine at 20. problem fixed.

 

cap, rotor and plugs replaced. All is well.

thanks guys.