m54b30 misfire diagnosis process

The purpose of this post is to explain my diagnosis of the misfire problem my car developed. So my 2003 330xi threw a misfire code, and began to idle funny. I drove it home, and began to try to diagnose the problem. My code reader pulled a p1347 code. Misfire with fuel cutoff. I cleared the code, restarted the car, and reproduced the problem. Car was idleing super rough, and would get bad enough it would almost die. I pulled codes again, and this time showed 3 cylinders misfiring. I repeated the process a few more times, and eventually ended up with all 6 cylinders reporting a misfire, and also receiveing a lean fuel mixture code for each bank. Following codes were pulled.

p1083 - lean fuel mixture bank 1

p1085 - lean fuel mixture bank 2

p1343 - misfire cut fuel cyl 1

p1345 - misfire cut fuel cyl 2

p1347 - misfire cut fuel cyl 3

p1348 - misfire at start cyl 4

p1351 - misfire cut fuel cyl 5

p1353 - misfire cut fuel cyl 6



Car background. I just purchased this car about 3k miles ago, and did a bunch of cooling system maintenance on it the other day. Replaced the water pump, thermostat and housing, oil filter tower gasket, coolant temp sensor, radiator hoses, belt pulleys, belts, oil, coolant, etc...

Car was running very well, except for a slight whistle at part throttle. Back to that later.

So my diagnosis process was as follows.

I knew right off after repeatedly pulling codes that the problem was not due to ignition components for one particular cylinder. For it to have rather suddenly gone bad in all cylinders led me to believe the problem stemmed from the air fuel mixture itself, and not the ignition components. (if your dme goes bad, that could provide similar symptoms.)

So I decided to check my fuel pressure. Initially I was thinking that it perhaps was the fuel filter. I had no records from the previous owner, so I have to assume that the filter has not been changed. The car does have a new fuel pump. So I don't have a fuel pressure gauge, but I have a simple air pressure gauge that works fine. I showed 50psi, and did not fall off as idle problem worsened. Looks ok there.

So if it is getting plenty of fuel, and I think the ignition components are ok, the next thing to look at is the air supply. I have experience with turbo cars, and know that any discrepancy between what the dme thinks is going into the car, and what is actually going into the car can cause problems. It was at this point that I remembered my slight whistle at part throttle, and so I googled it, and sure enough, people talk about the lower intake boot cracking. So I started pulling the intake apart, and inspecting the intake boots. The upper boot was showing signs of pending cracks, and low and behold, the lower boot had a pretty serious crack going to the idle control valve. This meant that the engine was pulling in more air that the meter reported, and thus running lean. That explains my codes.

While I was in there, I yanked out my DISA valve, to inspect, and it was toast. I am lucky none of the parts fell into the intake of the car.



I have ordered an upper and lower intake boot, and a German Auto Solutions disa upgrade repair kit. I am no engineer, but that kit looks pretty damn good to me, and for half the price of a disa, I figured I would give it a shot.



Parts should all arrive next week after labor day, and I will install them and report back, but I expect that this will solve my issues.