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E12 L-Jetronic FAQ

Updated 5/04/2002

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Compiled by Peter Florance; courtesy of the respective authors

All US spec BMW e12 cars (and many 2.8L and larger cars in other markets) were equipped with Bosch L-Jetronic fuel injection. I've consolidated a list of the site's FAQ articles here as a stepping off point.

If you have a 530i, the vacuum hose routing can be confusing. Here's a CA spec car's vacuum hose diagram scanned right from the underhood decal.

For those not familiar with Bosch L-Jetronic fuel injection you may want to start with L Jetronic Seminar in PDF format. This was a Microsoft Powerpoint document, presented at the 1999 E12 Fall Fest in Virginia Beach, VA. The seminar will open in a new window. If you'd rather download it, right click on it (Windows users) and left click on the selection "Save As" or "Save Target As..." and pick a location on your local hard drive.

A complete electrical diagram of the 528i fuel injection system is available here as an Adobe Acrobat PDF document. If you'd rather download it, right click on the link (Windows users) and left click on the selection "Save As" or "Save Target As..." and pick a location on your local hard drive. This is a drawing in a 11" x 17" format but is only about 22kb in size.

For more technical reference, here is some common component pinout information: L-Jet ECU, Engine Harness and Combo Relay Pinout Very helpful for those converting carb'd cars to Ljetronic as the engine harness connector is a great place to interface to the entire 528i fuel injection and ignition system.

One electrical component that has started to cause some problems (no start, no fuel pump, etc) in these older cars is the Combo Relay. We've given the Combo Relay Repair it's own FAQ and pictures here.

Speaking of age related problems, the fuel hoses crack with age. Leaking fuel under high pressure can make one heck of a fire, so replacing these hoses should be the highest priority. Here's an FAQ on fuel hose replacement.

If you are tuning the car, a good place to start is the L-Jetronic Throttle body adjustment FAQ available here.

Warm up idle speed problems are sometimes the result of Auxiliary Air Valve failures. Read about them here.

Later we'll list some common questions and links to the answers.


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