rough running 450SL
 

I have a1979 450SL V8 FI with a running proble. When I start the engine it runs fair for about a minute then the engine starts run rough. If you try to push accelerator any at all it will go dead.

I have replaced the plugs, cap, rotor, wires, and the fuel filter.

I have done all that I know to do. Maybe somebody has seen this type of problem before.

Check battery voltage and condition. Clean any corroded terminals especialy the little extra wire on the POS terminal. Check fuel pressure and volume. Check for vacuum leaks. Could also be the main computer (didn't call em PCMs back then) going south. Good luck.


Peter

Most likely a vac leak, so the system goes way lean off warmup.

Check idle control hoses, brake booster line, tanny vac line, and the supply fittings for the rest of the vac system (emissions, AC, door locks).

Be aware that a blown diaphram or two in the door lock system (hardly unlikely at this age!) will create a serious vac leak.

Other possibilities are the seals on the injectors or the seals between the intake and mass air flow venturi, or a bad fuel pump or filter.

No computer on a 79, it didn't have an O2 sensor.

A weak ignition is also possible -- pull a couple of spark plugs and see what the look like. Evidence of rich running can mean defective ignition -- strong enough to run with a rich mixture, but fails when it leans out.

It's also possible you have defective warm up regulator, going over-lean after warmup -- you will need to check the fuel distrubutor pressures.

Peter

Peter,

You got me on the computer. For some reason I was flashing on EFI which ended in 75. I'll second all your suggestions. I don't know how he will be able to check primary and control pressure without the special setup required.

Peter