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BMW 318i With An Erratic Speedometer

Q. Hi! Wonderful site! Have 1994 BMW 318i with erratic speedometer, mostly goes "full range" (pegs) and the fuel MPG gage follows, similar. Odometer follows as well, hyper-reads mileage. With this, the car "governs down" when 55 to 60 mph is approached, power loss does not happen on rare occasions when gauges working okay.

BMW 318i With An Erratic Speedometer

Otherwise drivability is fine, just distinctly loses power and will not go over 55 or 60 mph. Saw similar problem in your articles about 1986 with tach / MPG gage problems, wonder if similar? Would be nice if BMW had Tech Bulletin that covers. Appreciate any help. Thank you for considering.

Jeff
Brooklet, GA

A.

You're right Jeff, it would be nice if there were a TSB issued for this problem. Unfortunately there aren't any. So the first thing to do is to see if any codes are stored in the Powertrain Control Module (PCM).

Here's how to do it.

BMW 318i With An Erratic Speedometer

ENTERING SELF-DIAGNOSTICS:

  1. Switch the ignition to the run "ON" position.
  2. Depress the accelerator pedal five (5) times to the wide open throttle position within five (5) seconds to display flash codes for DME control unit 1. The accelerator pedal must be depressed six (6) times to display the flash codes for DME control unit 2. NOTE: Since the BMW V-12 engine uses two independent DME control units, fault codes and procedures must be followed for the specific system. DME system 1 fault codes affect cylinders 1-6. DME system 2 fault codes affect cylinders 7-12.

    • tR = 5 sec. preparation for read-out
    • tWS = 0.5 sec. wait for synchronization
    • t1 = 2.5 sec. additional check engine lamp check
    • t2 = 2.5 sec. wait for read-out
    • t3 = 0.5 sec. check engine lamp on
    • t4 = 0.5 sec. check engine lamp off
    • t5 = 2.5 sec. time between code digits
    • t6 = 2.5 sec. time between different codes
  3. Read and record all fault codes that are displayed. NOTE: To achieve good mid-range torque characteristics, long air intake pipes are used. This method of induction requires that the plenum chamber for the left bank (cylinders 7-12) be mounted on the right side of the engine, and the plenum for the right bank (cylinders 1-6) be mounted on the left side of the engine. The technician must keep this in mind when referring to component locations and testing procedures. Components such as air intake sensors, air mass sensors, injectors, throttle position motors and induction systems may be misdiagnosed because of possible confusion. Remember that fault codes will always refer to the DME system (DME system 1 = cylinders 1 to 6) and (DME system 2 = cylinders 7 to 12).

Hopefully there will be some codes stored indicating a problem somewhere. Otherwise it may be a bad Vehicle Speed Sensor in the instrument cluster.

Additional Information provided courtesy of AllDATA

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