misfire fixed with scan tool

[bartelbe]

This is the second 528i that when doing a simple reset with my scan the problem goes away. I will explain, I recently finished a engine overhaul which also turned into a trans overhaul so after racking up some miles and changing the oil and filter I decided it was time to put my foot into it to see how it pulled and shifted under high load and rpm. Normal driving the car responds perfect engine and trans, now when accelerating it seemed like the engine was lacking power and once the engine got up into the higher rpms it started to fall on its face to a point were it almost died and then it slow came back which I am leaning towards either a fuel pump, regulator or filter. But this is were it gets interesting when the engine did this the check engine light came on and was blinking, never seen one blink before? so when I used my scan tool to read the code which was misfire #3 and the engine was missing but the code was not pending so I reset it and the code went away along with the misfire and the engine started running smoothly! !!. My other 528i did the exact seem thing were the engine mis would go away when clearing a fault code. I believe what is going on but need some confirmation and that the dme is actually "shutdown" a mis firing cylinder to protect the cats and upon resetting or clearing the cylinder comes back is this correct? And if so wouldn't 2 cylindes be cutting out.

[rf900rkw]

"Misfire with fuel cutoff" is exactly what you describe. Once the DME sees a misfire that is bad enough to put the cats at risk of damage or fire, it will cut fuel to that cylinder for the duration of the drive cycle. Clearign the code will bring it out of the mode. So will turning the engine off for a few minutes.

[edjack]

That does not seem to solve the root cause: What prompted the misfire in the first place? And why won't it come back?

[tmvE39E53Z32TT]

I think maybe he hasn't put his foot on it again. Maybe just fuel starvation at high rpm run.

[bartelbe]

QUOTE=edjack;27174184]That does not seem to solve the root cause: What prompted the misfire in the first place? And why won't it come back?[/QUOTE]
The root cause I suspect is fuel starvation for a number of reasons one being each time I have duplicated the misfire is random. I have not really dug into the fuel system yet "its ice fishing season" but I plan on looking at the vacuum line goinv too the regulator as well as fuel pressure. I was more confirming a theory about what was going on when resetting dtc which doesnt actually fix the root cause. If you remember a previous thread about ghost codes, where a mis would develop and the check engine light would come on but no code was listed when checking and reseting the mis would go away the root cause of this one was a spark plug but when this one did sonething similar it got me thinking and randy confirmed my theory.