bmwcrocop

Would 87 gas cause engine misfires and the engine light to come on?

alx

No. You will just observe reduced engine output due to retarded timing (to avoid detonations under engine load). However, bad gas can cause misfires that if bad enough will light up the check engine light

bmwcrocop

MB has had the car for two months and they were able to replicate the issue of misfiring at start.

MB said they found a gasket that was installed backwards -- by the secondary air pump on the left side of engine.

thinks it's causing misfires as it's blocking air.

thoughts?

alx

secondary air pump is used only to speed up cat light up. it stops working after about 90 seconds on a cold start.

if your misfires are only in the beginning then the dealer's theory is a plausible one. if you are getting misfires after the first 90 seconds - the air injection pump is not the culprit.

GPrime2

It's possible if the valve is stuck open that the downstream O2 sensor is reading a/f mix and sending an incorrect reading to the computer causing an incorrect mix and a misfire. I would sincerely doubt it though, the amount of air being pumped in by SAIR is not much compared to the engine's exhaust.

bmwcrocop

It has been confirmed the misfiring problem was solved with fixing a warped manifold and broken lever and further fixing the backwards installed gasket by the secondary air pump.