Glow Plug - Preglow System Testing

84mercedes01

TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS


DATE: February, 1984 REF. NO. 15/23

SUBJECT: QUICK START PREGLOW SYSTEM ENGINES 616 AND 617
A. TESTING PREGLOW SYSTEM WITH INDUCTTVE CLAMP-ON AMMETER
B. INSTALLATION NOTE FOR PREGLOW TIME RELAY


A. Testing Preglow System with Inductive Clamp-On Ammeter

Testing of pin-type glow plugs with an ohmmeter, according to Job No. 15-510, can be an effective quick test to determine if a glow plug is inoperative. However, this test is not sufficient to determine glow plug heat output; low output may cause difficult engine starting, especially in cold temperatures.

A simple supplementary test can be performed to measure current draw of each glow plug using an inductive clamp-on type ammeter, such as the SUN DMM-5 digital multimeter.


Test Procedure

1. Clamp inductive ammeter pick-up around lead of pin-type glow plug.

2. Turn ignition key to preglow position "2". The ammeter value should be 8-15 amps, measured after a preglow time of 10-20 seconds. If the measurement is greater than 15 amps, replace the glow plug. If less than 8 amps, check glow plug lead for continuity; if O.K., replace the glow plug.


B. Installation Note For Preglow Time Relay

Extended storage of a preglow time relay (check production date) may shorten its specified preglow time and prevent the engine from starting. After the installation of a new relay, preglow repeatedly (approximately 5 to 10 times) until its condenser energizes sufficiently to reach the specified preglow time.