76 450SL No Start, floods out - PeachParts Mercedes-Benz Forum

griffins45619 · #1 09-10-2010, 12:39 PM

My 76 450SL is flooding when cranking to start. If I pull the fuel pump relay and try to start after cleaning the plugs off, it will hit and fire but not run, even on the residual fuel. It's almost as if the fuel pressure is too much and the WUR is not compensating. I don't have the gauges to test the WUR pressure but need to get this running quickly. It ran previously but very rough and would not accept throttle response after about 1/4 throttle. Any ideas?

meltedpanda · #2 09-11-2010, 08:55 AM

assuming this is a KJet < I would check the cold start injector, if it fails to open it it much like a choke failing to close, too lean , no start, this is closely realted to the thermo time switch, check both. Airflow sensor plate could be stuck or plunger stuck?
If it starts and runs for a bit then dies, you may be correct on pressure , either total system pressure or warm control pressure

griffins45619 · #3 09-11-2010, 10:06 AM

Thank you for the reply. I have disconnected the cold start valve and still have the same issue. I did check to make sure the plunger is working up and down as it should. It will not start to run and then die. Just total flooding. I disconnected the number one fuel injector line and after stopping cranking, it will still continue to feed fuel for about 10 seconds before shutting off. I'm leaning towards the WUR not reducing the fuel pump pressure and causing my issue.

meltedpanda · #4 09-11-2010, 11:22 AM

disconnecting it would defeat the purpose, failing to open starves the initial start up from getting the petrol it needs

rowdie · #5 09-11-2010, 01:49 PM

That is normal if the line continues flowing. You are just relieving system pressure.

ctaylor738 · #6 09-13-2010, 08:09 AM

The WUR has nothing to do with "fuel pump pressure." It regulates control pressure. A lower control pressure allows more fuel to flow to the injectors during warm-up by making it easier for the air sensor mechanism to move the pin in the fuel distributor.

You may have high system pressure. A common cause of this is a plugged fuel return, either in the line or in the FD. Unhook the return line, put it in a can or bottle, jumper the FP relay and see if you get a good flow.