Emissions - Delayed Throttle Response, First 3 Minutes

Group 13
Fuel System



Bulletin Number
13 05 92 (3682)



Woodcliff Lake, NJ
January 1993
Product Engineering



SUBJECT:
M50 Engine - Driving Characteristics During Warm-up Phase

MODELS:
E34 525i/iA/iA-Touring, E36 325i/iA

Situation:
Depending on ambient and engine temperatures, the above models may exhibit delayed throttle response during the first three minutes of operation. This phenomenon is a result of deliberate changes in the air/fuel mixture and ignition characteristics to reduce emission levels during the warm-up phase.

Cause:
In order to gain maximum efficiency and maintain reduced emission levels, a heating program for the catalytic converter is employed.

The heating program involves the use of a lean mixture in conjunction with a retarded ignition angle during the warm-up phase. Combined, these changes produce increased exhaust gas temperatures allowing the catalytic converter to reach its operating temperature after only a short driving distance.

This means optimum engine efficiency in conjunction with maximum protection of the environment.

Action:
In the event of a customer complaint, the reasons behind this phenomenon should be explained to the customer. It should also be stressed that this program is only active during the warm-up phase and that it has no negative effect on the length of the engine's life.

Any attempts to correct this situation (i.e., checking the air intake system for leaks, testing fuel pressure, ignition coils, and spark plugs) should only be made if the car exhibits extremely poor driving characteristics during the warm-up phase.