I have been trouble shooting a hard start problem on my 300CE. The hard start takes two to three tries, or it would stall as soon as it is started. There are no fuel smell under the hood.

Here is the symptom:
Hard start in the morning, or after a few hours
No problem if stop for a few min, such as refill gas at a gas station

What have been done.
Adjusted EHA valve, small black box behind fuel dist
Swapped out EHA valve and fuel pressure reg with another car
Replaced fuel filter and fuel accumulator

Jack

Jack, what's the condition of your distributor cap, rotor, ignition wires and sparkplugs?

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Fred Hoelzle

Did you replace the one-way valve (~$30) on the discharge side of the pump? You may need to hook a pressure gauge setup on the fuel system to check residual pressures at the time of the hard start, but it may be your fuel system leaking down. I've also seen fuel pumps that started fine after running, but wait about 10 minutes or more and the commutators will not allow motion or the bearings are seized enough to require multiple tries to engage the fuel pump. Make sure the fuel pump is cycling when you turn the key over, and cycle the key a few times to both listen for the fuel pump engage every time, and to pump the system up so it will start right away.

I also have seen the fuel injection coolant temp sensor (located on water pump, with big black snap-on plug) go bad and cause similar problems.

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Don't ask me, I'm a shop-owner by default

Thank you for the replies.

I Pick up a ckeck valve today. It is raining, and the driveway is wet. I will install it tomorrow.

Jack

After all the parts swaping, monitoring, and troubleing on cold hard start on my 92 300CE. I swap out both EHA and fuel pressure reg from my 91 300E. I also adjusted the EHA, but there were no improvment. I was sure my problem was fuel pressure related.

I sent my wife to pick up 2 fuel pump check valves from my local part distributor, she return with only one valve. As I wanted to know the result, and do not want to wait another day. I replaced valve on pump no 2. To my amuse, the cold hard is gone.

Jack