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Friday, December 19, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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Thursday, January 8, 2009

Catalytic Converter Replacement

While on my way to my uncle's house for Christmas dinner the CEL illuminated again. It didn't take long to realize a) what caused it, and b) that I would be spending a considerable sum of money in the very near future. Of course, the car didn't skip a beat and I completed the trip without incident.

The following day was a company holiday so I used the spare time to order the parts necessary for the repair. First on the agenda was a visit the dealer's parts department to order a new mid-section. At a discounted price of $1850 including tax the part wasn't exactly a bargain but the dealer made the purchase relatively painless by giving me Tischer's price -- a full 20% off the list. After briefly watching my technician trying to repair one of those stupidly complex panoramic sunroofs from an X5 I hopped in the car to do a few errands before arriving home to do a little parts surfing.

What parts, you ask? Whenever the exhaust is dismantled BMW recommends all new assembly hardware including special self-locking copper alloy nuts used to attach the midsection to the headers, header flange gaskets, and sealing rings that help bridge the gap between the mid-section and muffler section. In addition, common practice is to install new O2 sensors with new cats, but since I already replaced the pre-cat sensors a couple years ago I only had to grab two sensors to replace the post cat units.

(Image: Closeup of new catalytic converter installed on E36)While looking at my maintenance schedule worksheet I realized that the exhaust mounts were about 10K miles short of their 90K replacement interval. Since I was not interested in dragging two grand worth of exhaust on the ground I ordered two new rubber mounting rings as well as two new exhaust hangers and related hardware.

And just before I clicked the "Checkout" button I remembered that several months ago while I was under the car I noticed the black plastic raceway used to protect the post-cat O2 sensor wires had started to sag. I figured this was due to a failure of the raceway's integral mounting clips and decided that the $10 replacement cost for the raceway and cover was well within reason.

When it came to the installation I broke with tradition and decided to have my technician do the work, primarily to get the full two year parts and labor warranty. Sure, I could have screwed around in my bitterly-cold garage for the better part of an afternoon but for the two hours the dealer quoted to do this job it just wasn't worth it to me. So I arrived at the dealer this morning and checked in with my technician to let him know about the big bag o' parts in the car before jetting off in the loaner to get to work on time. I picked the car up in the evening and after a 15 minute drive home I got out and walked around the car with the engine idling. The first thing I noticed was that the occasional, very faint rattling noise coming from the cat heat shield was no more. The second thing I noticed quite by accident as I examined the muffler is that the exhaust actually smelled like, well, nothing. It was very dry and sooty, but did not smell like the exhaust output of the vehicle prior to the repair. Apparently these cats actually do something. :-)

Now for the fun part -- the cost analysis. Total of incidentals from Tischer was $456 including shipping and their discounts resulted in a $150 savings over list price. The cat normally retails for $2100, so including shipping I managed to save approximately $250 on that part by walking up to the parts desk and ordering it ahead of time. Had I simply walked in off the street and asked the service advisor to replace the cats I would have paid full list for that part. Installation labor was two hours at $120/hr plus SST, or $256. This brings the total for this repair to $2562.

Who says owning old BMWs ain't fun?

Mileage: 171000, Parts: $2306, Parts Saved: $400, Labor: $256

Saturday, January 24, 2009

Tire Repair

I was deep into an offramp during the commute home earlier this week and I felt the rear suddenly come loose. Judicious steering and brake inputs settled the car in short order but at the time it felt very strange...not anything like a typical oversteer condition I've experienced on the road or the track. The rear felt particularly unsettled throughout the recovery.

I initially suspected I hit an icy patch but the roads were dry and clear, if not a bit salty. On the next straight patch of road I performed a couple of quick lane-change maneuvers to see if I could duplicate the conditions but was unsuccessful. I drove the remainder of the way home thinking perhaps one of the (original) trailing arm bushings decided to give out at the ripe old age of 172K miles and that caused the arm to flop around a bit under load, affecting the rear alignment in the process. When I got home I walked around the car a bit but found nothing out of the ordinary aside from what I perceived to be a slightly greater bulge in the sidewall of the left rear tire. Given the effects of cold temperatures on tire pressures I didn't think much of it at the time.

This morning I decided to brave the 37 degree air and wash the car to rid it of the 60 pounds of salt it had collected over the past week. As I got around to cleaning the left rear rim I noticed that the bulge in the tire sidewall had grown. I knew full well what this meant and it didn't take me long to find the nail, which had been squarely driven into the tread of the tire about 2" from the sidewall. While some might interpret this as bad news I was actually relieved that the damage occurred where it did because it meant the tire could be salvaged with a plug patch and remain in service until the end of the season -- at which point I had plans to decommission the entire set anyway.

Of course, having discovered this on a Saturday at around Noon meant scrambling to find an open tire shop. To make a long story short, the third shop I tried agreed to patch the tire just before they closed for the day so I quickly got the car into the garage, put the rear up on jack stands, pulled the tire, and brought it over to the tire shop. Since I brought the tire to them "loose" and they didn't have to jack up the car or put it up on their lift they only charged me $15 for the fix. About an hour later I had managed to get the tire back on the car, all the tires brought up to my winter tire pressure of 33 pounds, and a short test drive completed successfully.

So what did I learn today?

Track junkies know full well that one way to increase an otherwise neutral car's tendency to oversteer is to decrease the tire pressure in the rear relative to the front, by a few PSI. My episode on the off ramp proves that this works. Incidentally, the effect of greater pressure in the rear is predictable -- less oversteer (or more understeer) -- and this is one of the main reasons why BMW now insists (to a fault, in my opinion) that tire pressure be as much as six PSI higher in the rear.

Mileage: 171600, Labor $15