W111 Stumbling engine start, cold or warm - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 04-28-2016, 10:45 AM Thread Starter
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Vehicle: 1971 280SE 3.5 Coupe, 1973 280C
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W111 Stumbling engine start, cold or warm

I have a '71 280SE 3.5 Coupe - when I go to start the car, whether the engine is cold or warm, it really starts in a slow and stumbling way - very low revs, chugging, rocking.

However, once it gets going, the engine revs sweetly, plenty of power it seems.

The problem is worse when the engine is warm.

Do I have a fuel pressure or cold start valve problem?

Scott
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post #2 of 4 (permalink) Old 04-28-2016, 11:04 AM
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Fergusson, I would say that sounds like a fuel delivery problem. It could be your cold start soleniod valve. You might need to replace that. Also I would check your lines and filters, it might just be that the filters need some cleaning.
Good luck and keep us up to date on how this goes!

-Bergermiester
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post #3 of 4 (permalink) Old 04-28-2016, 11:24 AM
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Originally Posted by Fergusson View Post
I have a '71 280SE 3.5 Coupe - when I go to start the car, whether the engine is cold or warm, it really starts in a slow and stumbling way - very low revs, chugging, rocking.



However, once it gets going, the engine revs sweetly, plenty of power it seems.



The problem is worse when the engine is warm.



Do I have a fuel pressure or cold start valve problem?



Scott

Problem is worse when engine is warm (starting). But "once it gets going" it's fine. How long does the issue last?

What happens if you turn the key to the on position a few times to run the fuel pump for a few seconds (to build pressure and flush fuel in the lines back to the tank) before turning the key to the start position?

Early d-jets have an issue with warm starts due to a vapor lock condition where heat from the engine will cause the fuel to boil in the fuel lines if left sitting there. The fuel can vaporize in the injectors and fuel rails causing a lean condition at startup, even making the car not start in some cases. That's one reason I always turn the key a few times to get fuel flushing back to the tank. Get cool fuel from the tank into the rails.

It could be possible that either the check valve on your fuel pump is shot (or the pump is entirely incorrect).

It also could be possible that the fuel pressure is set too low. Many d-jet owners have compensated for the hot start issue by increasing the fuel pressure (and insulating the fuel lines too in some cases).

.

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post #4 of 4 (permalink) Old 04-28-2016, 02:54 PM Thread Starter
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Good stuff - thank you! I've ordered the fuel filter.
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