Fuel Distributor - Leakage Confirmation

91mercedes04

REF. NO. MBNA 07.3/18


TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: September 1991


SUBJECT: ALL MODELS WITH CIS-E FUEL DISTRIBUTOR LEAKAGE


We have received a number of warranty claims with the complaint of internally leaking fuel distributors. After extensive bench and in-vehicle testing of these fuel distributors, we have found that most of these parts are not defective.

When testing a fuel distributor in a vehicle, the only way to confirm internal leakage is by performing the leak test as described in our service literature.

A possible indication of an internally leaking fuel distributor is when the Lambda "On - Off" ratio readings at idle vs. 2500 rpm (1) cannot be brought within 10% of each other by adjusting the idle mixture adjusting screw.

If performing a visual check, please keep in mind that when pressing down the airflow sensor plate the control plunger is lifted off the seal which prevents fuel from leaking. By doing so, some fuel is allowed to seep down the plunger to act as a "lubricant" between the plunger and the plunger barrel in order to keep the free movement of the plunger.

Whenever the airflow sensor plate is pushed down and the plunger is lifted off its seal, it is normal for a slight seepage of fuel to be visible down into the intake. If the plate is held down long enough, a small puddle can form (note: with the fuel pumps shut off, the max. 2 cc content of the fuel accumulator can be pushed out).

Refer to Service Microfiche job no. 07.3-120 for all testing procedures.

Note: All warranty returned fuel distributors will be closely monitored. Non-defective parts will be returned to the dealer and the dealer's warranty reimbursement account debited.

(1) With purge line disconnected and plugged.