Exhaust System Back Pressure Check (18 02 99)

EXHAUST SYSTEM BACK PRESSURE CHECK

TECHNICAL SERVICE BULLETIN

SUBJECT

Exhaust System Back Pressure Check

SITUATION

A customer may have one or more of the following complaints on a vehicle with a restricted catalytic converter:

1. - "Engine has no power / looses power"
2. - "Rattling noise from under the vehicle"
3. - "Check Engine lamp is illuminated" and one or more of the following faults may be stored in the Engine Control Module (ECM/DME):
   1. Fault Code 40, 45 or 233 (E9 hex), 234 (EA hex) - Cat. - converter conversion / efficiency
   2. Fault Codes 63 - 74 (3F - 4A hex) Cylinder misfire detected.

Refer to service information bulletin 18 01 99 for further catalytic converter information.

CORRECTION

A common cause for high exhaust system back pressure is a restricted / blocked catalytic converter.

A new tool has been developed to check exhaust back pressure when a restricted catalytic converter is suspected thus eliminating unnecessary component replacements and excessive diagnosis times.

In this case it is not necessary to check for a restricted / blocked catalytic converter.

PROCEDURE

If the above customer complaints are received and a restricted catalytic converter is suspected:

1. Remove the pre-catalytic converter oxygen sensor as outlined in the appropriate repair manual, group 11 section 11 78.
2. Install the exhaust back pressure gauge hose connector in place of the pre-catalytic converter oxygen sensor. See Fig 1 .
   NOTE: Lightly tighten (snug) the tool fitting. Do not over tighten.
   Fig 1: Exhaust Back Pressure Gauge Hose Connector Installation

   
3. Mount the gauge in an upright position - the hose connection must be located at the bottom of the gauge for proper back pressure readings. See Fig 2 .
   NOTE: Incorrect test readings will be the result if the gauge is not in the upright position, for example: hung up side down, laid flat, etc.
   Fig 2: Mounting Exhaust Back Pressure Gauge

   
4. With the hand brake on and the vehicle in park or neutral, start the engine.

   The engine must be at operating temperature before measurements are taken.

5. Raise and briefly hold the engine speed at 2500 rpm.

   With the engine speed stabilized at 2500 rpm the gauge should remain in the green zone.

   TEST RESULTS:

   1. - If the gauge indicates readings in the green zone (less than 1.5psi) the catalytic converter is not restricted. See Fig 3 .
      Fig 3: Gauge Indication In Green Zone

      
   2. - If the gauge indicates readings beyond the green zone (greater than 1.5psi) the catalytic converter is restricted and should be replaced. See Fig 4 .
      NOTE: A restricted catalytic converter will typically indicate readings greater than 2psi during the 2500 rpm test as described above.
      Fig 4: Gauge Indication Beyond Green Zone

      

   NOTES:

   1. A non-restricted catalytic converter may momentarily indicate a reading beyond the green zone (up to approximately 2psi) when revving the engine rapidly from idle speed to 3000-4000 rpm.
   2. Also if the vehicle is driven with the gauge connected (not recommended) it will display readings beyond the green zone during engine acceleration (high engine load)
   3. A gauge reading beyond the green zone (greater than 1.5psi) is normal under these conditions due to the momentary back pressure build up in the exhaust system caused by the engine acceleration and does not indicate a restricted catalytic converter.
6. Reinstall the oxygen sensor as outlined in the repair manual, group 11 section 11 78 and clear all fault codes in the ECM/DME memory.

PARTS INFORMATION

The BMW part number for the new exhaust back pressure tool is 99 00 0 001 855.

Also refer to service information bulletin number 04 12 00 for further information regarding the exhaust back pressure tool.

The exhaust back pressure tool consists of:

1. Analog gauge
2. Connecting hose
3. Connecting fitting for oxygen sensor hole

   See Fig 5 .

WARRANTY INFORMATION

Information only.