Hard to start - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 08-28-2013, 12:01 PM Thread Starter
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Hard to start

I have a W108 1970 280 SEL 2.8 six cylinder fuel injected Mercedes. My problem is it is hard to start after sitting for an hour. It seems to be starving for fuel, but just as soon as it does start you can shut it off and will restart perfectly for at least 30 minutes. Is there some check valve that could be leaking down? I have changed air filter and fuel filter with no noticeable effect. I’m open for ideas!!!

1970 Mercedes Benz 280SEL
VIN 10801912050616

1967 Mercedes 250SE
Parts Car
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post #2 of 6 (permalink) Old 08-28-2013, 03:03 PM
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Texas. Hot. This is probably vapor lock, very common in these engines. You can try letting the fuel pump run for five seconds before cranking, then floor the pedal while cranking.

If this technique doesn't help, there are various options go fire the cold start valve while cranking to provide extra fuel.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #3 of 6 (permalink) Old 08-28-2013, 03:10 PM
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One issue you may have are injector seals. They're pretty easy to replace and to get to (and they're cheap). I did 8 of mine in an afternoon, and I had Makers Mark helping

I'm not sure if you have the same fuel pump as I do but mine has a check valve that went bad. When warm and after sitting 10 mins or so, the fuel drains back into the tank and I have a hell of a time starting it. Do a general search on the forum for this same thing, and you'll see someone replied with a Summit Racing check valve part number. For that matter, just about any aftermarket fuel system check valve would work. Recommend you call Summit Racing and see what they have...
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post #4 of 6 (permalink) Old 08-29-2013, 07:26 AM Thread Starter
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Thanks for the ideas, I think if I could activate the cold start valve manually it may help, but if there is no available fuel it may not. Think I will pursue the check valve first. Is this check valve an integral part of the electric fuel pump?

1970 Mercedes Benz 280SEL
VIN 10801912050616

1967 Mercedes 250SE
Parts Car
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post #5 of 6 (permalink) Old 08-29-2013, 11:13 AM
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Quote:
Originally Posted by jman1151 View Post
Is this check valve an integral part of the electric fuel pump?
Yes, for mine. i'm not familiar with whether you and I share the same model pump though. I suspect not ... Wish I could be of more help there
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post #6 of 6 (permalink) Old 08-29-2013, 03:07 PM
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Originally Posted by ctaylor738 View Post
You can try letting the fuel pump run for five seconds before cranking, then floor the pedal while cranking.
+1 on this suggestion, it's the easiest workaround until/if you decide to address the check valve or leaking injectors. I let mine go for more like 10-15 seconds and also only need about 1/4 pedal but otherwise the same technique. BTW the manual even says this is the proper way to start from cold for my series car, so maybe there's nothing wrong after all?

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