Misfire under load in open loop
 

K jet 81 380SL has a terrible misfire when warm. I unplugged the O2 and temp sensors and it runs much better but still misses some. If I get on it in second and let it pull through the gear it may miss once or twice. Ignition system all seems newer and spark is strong. So I'm assuming I need a new O2 and plugs to fix this?

I read about using this procedure on the 190 to test issues I had with that but I never saw any change with this because that turned out to be cam timing related.

Being an '81, check if it ever got upgraded to the double-row timing chain. If it still has the single-row and it's stretched, well - you could have cam timing problems!

The EZL can get a bit crappy too. I fought with misfires and missing out for years in my SL. Had a good strong spark and all seemed well, but the EZL was just firing whenever it wanted to and finally died. With the new EZL installed, it's run like a top ever since.

Im helping a friend out so I'm not sure about the chain but I'll look into that. Ezl is a good suggestion too.

Timing looks right and I have the O2 sensor on order with plugs so we will see if that solves the issue.

It is still single row. I'm not trying to get that deep into this but its lower mileage and the timing doesn't seem to be off from wear.

Put a new O2 and plugs in it and hooked it all back up. Missfire is still present as it was in open loop but the closed loop issues are fixed. Going to look at ignition parts now.

Keep in mind that the fuel system is largely mechanical. If it isn't running properly open-loop, it probably won't closed-loop either. Might be a good idea to check if you have a dead spark plug on one cylinder, or a vacuum leak at one of the intake runners.