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Old 09-25-2009, 10:41 PM
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Join Date: Aug 2009
Posts: 14
Starting and rough idle

1987 560sel.Has a rough idle but runs great.Also has a slight starting problem.When I shut off the engine and crank it up within a few seconds it starts fine but still idles rough.If I leave it off for a little more than a minute or so, I crank it and it starts but dies right away.I then crank it again and it starts fine but still idles rough.Is there a check valve in the fuel system that keeps it pressurized after shut down and would the rough idle and starting problem be related.

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Old 09-25-2009, 11:23 PM
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Join Date: Jul 2008
Posts: 1,236
Hi there.... Funny, I'm sort of in the same boat as you at the moment. Here's what little I know about these fuel systems. First, I don't think there's a check valve per se, but there is an "accumulator", which is a spring loaded diaphragm deal that stores fuel pressure. It is located above the fuel pump. If the diaphragm tears, then the pressure can leak down when the car is stopped.

You want to do a fuel pressure test, to make sure pressure is normal and is being held when the car is off.

If you notice a leaking down of pressure with the car off, then there is a leak somewhere. That could be the accumulator, the injectors, the fuel distributor or a fuel line. The accumulator can be made to not leak without removal by pinching off the return line to the tank. A temporary way to see if the diaphragm is torn by comparing symptoms before and after.....

It sounds like fuel is leaking into your cylinders when you turn the car off, causing a temporary flood condition.

Also, make sure your air meter flap is not sticking.

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Old 09-25-2009, 11:34 PM
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Join Date: Aug 2009
Posts: 14
would the leaking into the cylinders create a rough idle.I am assuming this would mean the injectors are leaking?

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