My 1988 300E used to start immediately first thing in the AM. Now it needs to crank a few seconds more before its initial start. The rest of the day it's fine, even after 8 hours of sitting. If I crack the fuel line into the fuel distributor should I get an under pressure spray or just a fuel drip whilst engine is off?
Car has just over 100K miles and I recently replaced the fuel pressure regulator and I only use Bosch parts. Thanks.

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1988 300E

What is battery reading at after sitting over night? Also, could be starter ststarting to go

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1990 190E 3.0L

First go through all the fuses ,turn them in their holders .If you still have the white metel type, then you need to change them for copper or brass . Now check all earth points,remove them one at a time.Clean the conntact area and put a dab of grease on before you refit them.Then look at all your small vacuum pipes for split in any rubber joining ellbows. Another item to look at is your OVP relay ,it sits at the back of the battery .You will have to pull the plastic membrain off to see at the back .The OVP as a fuse on the top,check the fuse or fuses some have two.Then you can come back, let us know how you get on.

One cause of slow starts after sitting overnight is a drop in the system fuel pressure. There is a fuel accumulator by the fuel pump that can fail or you could have an injector leaking down (including the cold start injector).
I had the same problem with my M103. New injectors was the solution.

Why was the fuel pressure regulator changed?

The injectors are recent but the cold start injector is original, I will check that first. Thanks. I can't remember exactly why I replaced the pressure regulator.

OVP, fuses, starter and battery fine. Fuel pressure drop overnight sounds right.

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1988 300E

Next morning, turn the ignition on a few seconds without cranking the engine so the fuel pump cycles on and off. Do that 3 or 4 times. Then see how it starts. If it now starts right up, you know the pressure bleeds down overnight.

Thanks very much for the fuel accumulator test. I will try and hook up my CIS gauge as pictured. I now remember why I replaced the FPR, fuel was visible in the clear overflow tube. It had been that way for years, replacing it made zero difference in drivability.

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1988 300E

Thank you for that Rick i to have m103 with hot start problem. And came up with injector replacment as next job .But it will start as normal in the morning .

Tried that. Cycled the fuel pump ten times, still longish cranking before fires up.

Does this model have pressure a test port? You need to get a reading on the fuel pressure unless you just want to throw parts at it.

I have a CIS pressure gauge kit but not sure where exactly to connect it up.

Search for a thread started by me - fuel accumulator failure analysis. Either in that thread or a related one there a simple test to determine if the fuel accumulator is leaking internally.

It's a very overlooked part of the CIS-E system and a crack in the internal diaphragm can cause the symptoms you have, and it gets worse with time to the point where the car won't start at all.

Duke

See picture for fuel take off and the pressure in the second is ok .

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You must be joking.

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1988 300E

I was thinking that too. What does an oil change have to do with the problem and what is a starter refresh???