Authority on Five

Are You Smarter than a BMW Engineer?

Ever tried doing something to your car thinking that it is better than the stock part? Or, ever thought that the current enhancement can be further enhanced? Lastly, ever thought that some major part of the car's engine is faulty when there really isn't? During the last drive to Krabi, the car was not up to speed. It would take a while for it to pick up speed and there was some hesitation during the gears change-over. Using my OBD-II reader, the faults were related to misfiring and rich fuel mixture in the 2 banks. Remembering that my workshop did ever told me that the alternator was not performing at its peak, I diagnosed the problems to be related to an unstable current supplied by the alternator. Just to be sure, I bought an alternator tester and sure enough, it indicate that the charging was on the low end.

With all this information in hand, I headed down to the workshop confident that all would be well again after the alternator is replaced. As usual, my BMW engineer friend, Billy hooked up the car to the diagnostics machine. Not bad, my cheap OBD-II reader was right, there was a rich fuel mixture but the misfiring fault code did not appear since I cleared it with my OBD-II reader. However, this is where the similarity end. The OBD-II reader tells you the fault code but it does not tell you where the problem might be. That's why the diagnostics machine cost about tens of thousands of dollars while my OBD-II reader is less than a hundred. The rich mixture was caused by an air leak. A few prods here and there on the engine revealed everything was alright and then, lo and behold, Billy pointed to the cone air filter. He asked whether the problem occurred before or after I fitted the cone air filter. I was stunned and sheepishly said, ''After''. He smiled, took the cable out from the MAF sensor and told me to go for a test drive. I was supposed to put the cable back on the MAF sensor on the way back to see if there is any difference. Obviously, there was.

Without the cable attached ie. the engine is running with air from the cone air filter fed directly to the engine without MAF inputs to the ECU, the car was sluggish. When the cable was attached back to the MAF, the difference could be felt immediately. The present cone air filter is the stainless steel wire mesh type. Previously, I was using an Apexi Dual Funnel cone air filter, touted to be the best for filtration and air flow (with tests done to prove it). I removed the Apexi thinking that the wire mesh air filter would provide more air into the system, thus generating better combustion and hopefully, improve power. I was wrong, very, very wrong. Billy explained that cone air filters can create problems for the MAF because of the way the air is channelled through the sensor. The Apexi did not give me any problem whatsoever because it was properly engineered but the wire mesh filter was just 'a' filter. Apparently, since the wire mesh filter was much larger than the Apexi, more air was flowing through the system but the MAF was not able to read the input correctly because of the inconsistencies and thus, erring on the safe side, the ECU was prompted to pump more fuel, resulting in a .... rich fuel mixture!

A valuable lesson was reinforced today. I have always advocated keeping the car stock. However, I am unable to find  the original air box that I took out when I fitted the cone air filter system. There is nothing wrong with the cone air filter system, it works very well as it had been proven many times. If I had left the Apexi cone air filter alone, none of the problems I faced during the drive to Krabi would have happened. This has been a most humbling experience and I have learnt that:

a. Handheld OBD-II readers are good but diagnostics machines are better.
b. If it ain't broken, don't fix it.
c. Stock parts are the best parts.

There was some noise coming from the transmission system also. Some whirring and clunking sound could be heard when slowing down or downshifting. Billy said that its probably the prop shaft as this was one of the E39s common failure. I believe him. Afterall, I am not smarter than a BMW engineer. The car will go in next week to have the worn out parts replaced. I am sure everything will be as good as new again once that is done.

posted by gabey @ Wednesday, March 03, 2010