Hello,
Restrictions in the fuel delivery lines will cause changes in the sound of the electric fuel pump. A dirty fuel tank screen and especially the fuel screen in the electric fuel filter will change the tone of the electric fuel pump. The first step to solving any chronic starting problems is to be sure the fuel supply and volume is correct. Make sure the fuel tank screen, electric fuel pump screen and main fuel filter are clear. Check the volume and fuel pressure at the engine afterward. The earliest versions of the electric fuel pump on the 230SL did not have the screen built in them.
Most of these engines have the injection pump enrichment solenoid. This will activate any time the starter is activated. Make sure this solenoid and its relay is working. This will effect hot starting if it is not working properly.
I recently worked on a W113 which had chronic hard starting problems for years. The injection system was set much too lean and after sitting for about 20 minutes would not restart. The rise in engine temperature after shut down causes the WRD to lean out the fuel mixture even more, causing the hot start problem. The spark plugs were "snow white" indicating the much to lean mixture. After the mixture was richened the spark plugs showed a nice tan color and the hot start problem disappeared.
Joe Alexander
Blacklick, Ohio
