This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
The Motronic system (also called the Digital Motor Electronics or DME) is hands down the best overall fuel injection system that you can use when you consider price and performance. Ignition timing and fuel delivery are all controlled by a digital map that is recorded in a removable chip within the main fuel injection (DME) computer. The computer takes input from a variety of sensors that are located on the engine - cylinder head temperature, altitude (ambient air pressure), crank angle, throttle position, exhaust gas oxygen (mixture), ambient air temperature, and mass air flow. The DME chip is programmed from the factory with certain performance characteristics (mostly conservative) so that the engine will react well under a host of varying conditions. Major changes to the engine (including the addition of different camshafts) require an updated chip map to take full advantage of these modifications. Failure to update the Motronic system may actually result in a decrease in performance, as the original system is finely tuned to supply the correct timing and fuel injection values for a stock engine configuration.
Each system is matched directly a specific engine configuration. Because of the proprietary nature of the Motronic system, there isn't a whole lot of changes that you can perform without updating the DME chip. Major changes to the engine (different camshafts, increased displacement) will not work well with the stock Motronic system because the computer chip is designed to deliver the proper amount of fuel and spark only for a particular stock engine. To gain the maximum benefit from engine modifications, you need to either upgrade your DME chip, or install a programmable aftermarket engine management system.
The Motronic system is generally very reliable - its main failure points being the sensors that send data back to the DME computer. Another odd failure point appears to be the DME relay. Corroded contacts appear to cause this mission-critical part to fail somewhat intermittently. I have had many customers claim that their car runs much better right after they have replaced the DME relay. While I don't have any empirical data to back this up, there are a lot of people who will swear by replacing their DME relay once every two years. I do recommend that you carry a spare one, as well as a spare cylinder head temperature sensor, as the failure of either of these can potentially leave you stranded on the side of the road.
If you are running a stock engine with the Motronic injection, the best upgrade you can perform is the installation of an aftermarket DME chip (up through 1995). As stated previously, the factory programmed the original chip to compensate for a wide variety of driving characteristics. These days, you can find chips that will elevate the rev-limiter, advance your timing, and generally run the engine with less conservatism than the factory chip. The only downside to running a more aggressive chip is that sometimes the timing curves are a bit too advanced and may cause detonation on low-octane pump gas (as it is here in California). The E36 BMWs all have a knock sensor that will reduce detonation if the timing is too far advanced.
One downside to installing a performance chip is that you basically need to run premium fuel with the chip installed. Whereas the stock chip is designed and mapped to provide good performance across a wide variety of operating conditions, the performance chips are specifically mapped to assume that you are running high octane gasoline. If your car doesn't have a knock sensor and you run low octane gasoline with a performance chip, then harmful detonation may occur. If you run low octane fuel with a car that has a knock sensor, you will prevent detonation, but in general, you will not fully utilize the performance improvements of the chip.
If you have an OBD-II car (1996 and later), then the computer inside the car requires flash programming instead of the use of a chip. The Shark Injector Engine Software by Jim Conforti is a good choice for anyone seeking a little more performance out of their engine. The software upgrade alters the fuel enrichment maps, cam & ignition timing, raises the factory-set RPM limiter, accelerator enrichment, VANOS control, and optimizes other engine characteristics for increased performance.
Installation of a chip is a very easy process. The DME computer is located on the right side of the engine compartment (Figure 1). First, disconnect the battery. Pull back the rubber foam (Figure 2), and you will see the cover that protects the compartment (Figure 3). Remove the cover (four screws) from the compartment and you should see the DME and its harness. Pull back on the small lever on the harness, and you should be able to disconnect it (Figure 4). The DME is held in place by two clips - it should simply slide out (Figure 5). Place the unit on your workbench, and remove the four Torx screws (Figure 6) that hold the cover on. Then, flip the unit over and pry off the six tabs on the bottom. Don't be too concerned with damaging these tabs, as they aren't super important in holding the case together. With the tabs detached, pull the metal cover off, and you should see the circuit board (Figure 7). The chip is covered by a small piece of white plastic (Figure 8).
At this point, you might want to put on a static wrist strap, or merely touch something that's grounded (like a metal lamp housing or a radiator). In all the years of playing with electronics, I've very rarely had a problem with static electricity, but once and a while something doesn't work properly, and you can only guess as to why not. Carefully pop the chip out of the DME unit (Figure 9) and put the new one in (Figure 10). Make sure that the small divot in the new chip faces the same direction as the old one - it is possible to put it in backwards. Seal up the unit, reinstall it, hook up the battery, and you're done!
My rule of thumb is: it's best to find a chip manufacturer that offers a few different levels of performance, and will guarantee that you will be happy with the system.
Well, there you have it - a lot of work, but if you walk through it step-by-step and follow the photos I have published here for you, you should have no problems. If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs. If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one. Your continued support directly affects the expansion and existence of this site and technical articles like this one. As always, if you have any questions or comments about this helpful article, please drop us a line.