My recently acquired 1973 450SL has a starting problem. Some times it starts up and runs great. Other times it cranks normally but will not fire. I have played with the relays behind the passenger kick panel. I believe that I have determined that the main relay and fuel pump relays are the two upper most relays toward the fron of the car (or, when looking directly at the bank of relays they are the two that are up and to the left).

When I can hear the fuel pump pressurize the system like it is supposed to after the key turns to run then the car will start every time. When it does not pressurize it will never start. I tried swapping the main and fuel relays with other ones and it still starts sometimes but not others. When it is in the will not start mode if I jumper the fuel pump with an external wire from the pump itself or by removing the fuel pump relay and jumping there it still will not start.

Any ideas?

Brian Roth

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Brian Roth, Pollock Pines, CA
1981 300TD turbo diesel on 1984 Nissan 4x4 chassis. A runner.
1973 Porsche 914 with Ford 2.3 turbo. Not a runner yet.

...but my '73 450SE has a little button on the left side of the steering column that one is supposed to push "once?" if one runs into a cranking/no starting problem.

This was explained to me to be primarily for a "Hot Start" (vapor lock type) situation.

Don't know if your SL even has this button but I thought I would mention it.

Cheers!

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435