Engine Tuning For Emissions Testing

By Mike Perkins
BMW CCA/Houston Chapter Technical Advisor
Owner – Bavarian Machine Specialties

In our world today, your new generation BMW engine is controlled by a sophisticated motronic engine management system. The idea of a tune up seems somewhat outdated. In the past, a tune up consisted of replacing spark plugs and filters, adjusting valves, timing, fuel mixture and engine idle speed. It is important to understand that although most of these operations are no longer necessary on new BMW models, “tuning” is still the key to engine performance.

Although the definition of a tune up has certainly changed, the need for a well tuned engine has not. As of January 1, we have taken our first steps forward toward real emissions testing. Regretfully, the motorist choice emissions testing program is a watered down version of the failed I/M 240 program. Still your car will be required to pass an actual tail pipe exhaust analysis at idle and 2000 rpm.

Engine performance is the operative word when discussing a tune up on a modern BMW. When a customer brings their car in and asks for a tune up, I have learned that usually they mean the car is in actuality suffering from a performance symptom. The car may have a cold start or a surging problem, but they have been trained to believe “it needs a tune up”. In fact, all that may be wrong is a faulty coolant temperature sensor. In one sense, the tune up may be less involved than in the past, but in another, it is more complicated than ever before. There is a greater need for all components in the system to work together flawlessly. Sensors, actuators, spark coils, injectors, wiring connections, mass meters, variable cam timing, hydraulic lifters, closed loop O2 systems, dual catalytic converter systems, self diagnostic control units and vacuum air leaks are just the beginning of what should be considered when a BMW is not running properly. One sensor or wiring contact with slightly too much resistance can upset the entire balance of an otherwise perfect engine. Finding and repairing the glitch in the engine management system of a modern BMW is usually dependent on two basic elements; expertise and proper equipment. Without theses two important components, effective diagnostic procedures are futile. Fortunately, these systems while more complicated, are also more reliable.

Having conveyed all this about the complexity of today’s BMW management system, I would like to emphasize one more item that is of paramount importance and is a common ailment to all BMW’s. With fuel injection, even if all the components of the engine management system are functioning perfectly, the engine can still lack performance or perhaps even fail an emissions test. The most commonly encountered problem is with poor performance from the fuel injectors. You cannot and must not underestimate the impact of fuel injector volume and spray pattern quality on driveability. The diagnosis of “clogged” or “dirty” injectors are terms that can be somewhat misleading. The problem is caused not by dirt, but rather by a buildup of fuel varnish in the injector nozzle. The olefins (heavy waxy substances) in gasoline form deposits that gradually build up and restrict the injector. Although injector clogging is not as prevalent as it once was, thanks to the addition of improved detergents and other additives in gasoline, the situation still exists at a high rate. Bosch has even designed injectors to resist varnish build up. It is interesting to note that even though failing injectors will have a terrible impact on engine running, a fault code will not typically be set until the last stages of clogging. This fault code is never from the actual injector, but from the oxygen sensor that can no longer compensate for the extreme running abnormalities.

Generally speaking, there are two approaches to restoring injector performance. On the car and off the car cleaning. I have utilized both approaches and come to the conclusion that the only effective operation is an off the car method. This requires the use of a fuel injection cleaning/flow bench. It is more labor intensive due to the fact that the injectors have to be removed from the engine, but it offers several important advantages. In this procedure, the injectors can actually be observed during operation for an accurate spray pattern. An ultrasonic bath is also used to dislodge deposits in the nozzle and body of the injector that normally resist chemical cleaning. As an aside, it is interesting to note that Bosch does not approve the use of chemicals to clean injectors such as that utilized in the on the car method. Additionally, the cleaning bench allows for back flushing of the injectors and a set of injectors can actually be flowed and matched for a particular engine.

I have spent many hours on the flow bench and have discovered several interesting facts concerning the importance of fuel injector performance and the consequences on emissions output. My recommendation to anyone struggling with an engine that otherwise “checks out” but still has a running problem is to have the injectors tested. This might just save you a lot of time and expense, not to mention an inspection sticker.

Avoiding Expensive Brake Problems

By Mike Perkins
BMW CCA/Houston Chapter Technical Advisor
Owner – Bavarian Machine Specialties

In recent months, I have started to see more anti-lock brake system related brake problems. For the past decade, this amazingly effective system has, for the most part, been trouble free. As a reminder to club members, I offer some basic brake suggestions to avoid trouble.

First and foremost is to regularly flush the brake fluid system. BMW recommends that brake fluid be changed every two years. Since the advent of ABS in 1985, BMW recommends that all models use Dot 4 brake fluid (such as Castrol GTLMA). This brake fluid, as is the case with all Dot 4 brake fluid brands, is hygroscopic, meaning that it readily absorbs moisture when exposed to air. Moisture lowers the boiling point of the fluid and can cause brake fade. It has been estimated that in Houston, two year old brake fluid will contain anywhere from 4 to 8% water. This small amount will lower the boiling point by more than 25 to 30% which could cause compromised stopping power when it is needed most. In addition, moisture in the system can cause corrosion in the bores of system components, eventually leading to premature seal wear (i.e. leaking calipers, master cylinders, etc). Most of the ABS related failures that I have encountered can be traced to moisture contamination which leads to corrosion that can make the ABS valves stick. This usually requires expensive repairs that could have been avoided by periodic flushing.

Houston has more moisture in the atmosphere than do most places in the country. Because of this, I recommend brake fluid be tested for moisture content at least once a year. Flushing may be wise to do on a yearly basis, especially if the car is exposed to severe driving conditions (i.e. constant freeway stop and go, or racing/ auto-crossing). In fact, if a car is to be used at the track at all, I recommend the use of ATE Super Blue, which is still a Dot 4 fluid but has a higher boiling point than normal Dot 4 fluid.

While we are on the subject of alternative brake fluids, I still receive many questions regarding the use of silicone brake fluid. Anti-lock brake systems which are of the integral type that pumps fluid under high pressure (such as all BMW’s) should not use silicone brake fluid. Silicone fluid does not provide the correct amount of lubrication for the essential working parts of a master cylinder, calipers, or wheel cylinders. In addition, silicone fluid has a tendency to aerate when put in a pressurized situation. Any air bubbles in the brake lines will cause the pedal to sink drastically. Silicone fluid also repels moisture. Because many ABS controls and valves are made of stainless steel, attraction toward other ABS components made of steel happens at an accelerated rate. This could cause sticking or failure of the ABS unit.

While regular flushes are important, proper flushing is crucial. On an ABS equipped car, this requires cycling the ABS unit during flushing. The ABS pump holds fluid that will not be flushed unless the pump is run. Another way to insure an effective flush on all brake systems is to clean out the brake fluid reservoir. This should be done during every flush by removing the reservoir from the master cylinder for clean out with brake cleaner. You will notice a film of residue that has settled on the bottom of the reservoir; if this is not cleaned out you will simply flush this contaminate into the system.

My final recommendation is something that is often overlooked by both novice and expert alike. When working on brakes for any reason, do not force the caliper pistons back into the caliper without first releasing the caliper bleeder screw. Not following this simple step is inviting certain disaster and can have a dramatically negative effect on the longevity of the brake system. The calipers are located at the lowest point of the hydraulic system and tend to collect particles released from suspension in the fluid. Compressing the pistons forces this contamination back through the system causing other component failures. Always open the bleeder screw allowing contaminated fluid to escape before pushing the piston inward. Remember, it is better to strip a bleeder screw than to contaminate the ABS unit!

Houston BMW Parts, Service & Performance