Saturday, April 4, 2009
Another Year, Another E46 Blog Entry
I'm almost embarrassed to admit that my E46 blog only received a single entry for 2008, but for a couple of good reasons: I only put 700 miles on the car last year and did no maintenance other than an oil service and brake fluid flush exactly a year ago. Yea, I know...this borders on criminal behavior for a BMW driver but I really had no choice due to my crazy schedule and some changes in my living arrangements. It's now far less convenient to access the vehicle on a whim. I hope to solve that problem as soon as the real estate market returns to some semblance of reality.
I had meant to do an oil service six months ago but at that time I had put so few miles on the car I couldn't fathom throwing out what was effectively brand new oil, particularly if I had to pay to replace it. So, long story short, the penny-pinching environmentalist in me won out and I stored the car for the winter without changing the oil.
Last weekend I took the car out after all the salt had been washed off the roads by recent rains. Shortly after engine start the service engine soon (SES) light illuminated. I figured this might have something to do with the few gallons of old gas left in the tank so I checked my gas log to figure out when I last filled the tank. To my surprise it indicated my last fill up was in August -- yes, that's right -- eight months ago. Since I didn't want to drive around with a SES light and because I knew BMW would pay for the next oil service under warranty I made an appointment at the dealer for yesterday.
As the week progressed it became clear that the weather wasn't going to be very nice toward the end of the week and sure enough I woke up yesterday to a wind-swept rain. I braved the weather, had some fun testing the limits of DSC and quickly arrived at the dealer. By the time I managed to walk back to the bays to see my technician he had already brought the car in out of the rain. The first thing he said to me was "I'm surprised you're here!", so I naturally asked why. "Well, you don't usually drive this car in the weather like this." I smirked a bit but managed to respond in a completely unassuming manner "Hey, it's just a car, and I'm not THAT anal about it". His (all too correct) response?
"Yes you are."
The oil service was done in short order so he moved on to the fault diagnosis.
Exhaust Cam Fault (P0015) Diagnosis
The new diagnostics system that we couldn't get to talk to the E36 last time I brought it in didn't want to talk to the E46 either so my technician broke out the old standby GT1. That revealed only an exhaust cam timing fault recorded and no faults currently present.
He referred to the fault as a Vanos problem that most often occurs when the cars aren't driven enough. The oil bleeds out of the Vanos unit and lack of oil pressure in the Vanos unit for an extended period after start causes the Vanos to react too slowly. In this case the the sensor that tracks exhaust cam timing didn't see the expected change in timing within a set threshold and the DME recorded the fault as a "stiff exhaust camshaft". Because faults of this nature can cause driveability and emissions problems they typically have no thresholds. A single, transient appearance of this fault is sufficient to illuminate the SES.
At the time my technician showed me the diagnostics page he noted that the fault occurred at 7224 km. Not wanting to bother with math that early in the morning I did a rough conversion and figured that it translated to the mileage on the car as of last weekend when the fault occurred (around 5100 miles). I later realized, however, that 7224 km is actually 4488 miles. Current mileage is 5196. The last service occurred at 4586 miles. On the way home from that service the engine hesitated and idled poorly. While at that time I attributed the problem to old gas because everything returned to normal shortly after I topped off the tank with fresh gas, these symptoms are, interestingly, also associated with Vanos or cam timing sensor related faults.
So the question of the day is, if there were no other faults present (like misfires), and the exhaust cam fault was recorded at a mileage that occurred a year ago, why did the SES only first illuminate last weekend? More specifically, why was this fault recorded at almost 100 miles prior to the last service at 4586 miles...meaning, before I experienced the hesitation that was a most likely symptom of an oil-starved Vanos unit? This makes no sense.
There's not much I can do about the problem at this point other than drive
the car more often, and I had already planned to do that. If I get through
the year without any more related faults I'll consider this a subtle hint that
want need to be driven regularly.
STA-BIL and Techron
While discussing misfires and the chemical stability of modern gas my technician pointed out something I already knew but was perhaps reluctant to accept in the case of the E46. If I'm not burning the tank of gas within 60 days the car is effectively in storage and in need of a fuel stabilizer. He recommended the STA-BIL product because he said it worked very well for him in his motorcycle in the off-season, so I'll probably pick up a bottle of that when the time comes.
He also pointed out that BMW has made a point to tell technicians that the recently reformulated BMW gasoline treatment (which comes in a bottle that looks suspicously like Techron) actually coats the fuel lines, rail, and injectors with a substance that resists the formation of varnish and other contaminants. So while Techron is known primarily as a fuel system cleaner, it may also have properties to prevent damage to the fuel system from old gas. This is not to suggest that Techron or BMW's proprietary equivalent is a replacement for fuel stabilization compounds, but it may be good to use as preventative maintenance for modest periods of inactivity up to, perhaps, 90 days.