Hi Folks,

I've posted on w116.org but thinking I might seek some opinions here as well.

I think I've scoured every corner of the internet for K-jet information but perhaps I've missed something.

First let me say my car has new Spark Plugs, Dist cap + rotor, injectors, seals, refurbished fuel distributor, new fuel pump + filter , and a clean fuel tank.

My 77 450SEL starts fine sometimes and rough other times. When it's warmed up and has been running for a while I can shut it off, run out to a store and come back and it will fire right up.

If I let it sit for a couple hours it will start rough and chug for 5-10 seconds then even out.

Sometimes when its cold (sitting overnight) it will start fine, other times it will start and chug.

Now, if I unplug the blue plug on the fuel distributor before starting (I believe this allows the fuel pump to constantly run) It will fire right up. This leads me to believe there is a loss of pressure in the fuel system.

When I first start the car from cold, it makes a funny whirring noise for about 5 minutes.. Is this a normal air recirculation noise or is this a symptom of something being wrong?

Lastly, at approx 2,500 rpm (light throttle, just enough to cruise and hold speed at say 60 mph) the car seems to have a slight hesitation. This has gotten MUCH better as I've driven it a couple hundred miles but it is still present. Any ideas?

This is a classic symptom of a failed fuel accumulator. Its purpose is to keep the fuel pressure at a constant rate and to maintain pressure when the engine is stopped. When it fails, the engine heat will basically boil the fuel in the lines and fuel distributor causing a fuel starvation issue when the car sits and is restarted hot. Problems are worst 30-90 minutes after shutting off the engine hot. Conveniently, that's the amount of time you typically spend in a store...

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

ma:

1) Get this:
www.bentleypublishers.com/bosch/engineering.../bosch-fuel-injection-eng-mgmt.htm...

2) Taken collectively, the symptoms, as you suggest, indicate bleed-down/loss of pressure.

3) The overall mixture adjustment may be lean for the (effectively) new fuel distributor.

Yes I am definitely leaning towards the fuel accumulator... I have adjusted the mixture and am still seeing same issues.

Nothing constructive to add except I miss my '78 450SEL (not the mpgs though) and I have this that I don't expect to need again - https://www.amazon.com/Bosch-Fuel-Injection-Engine-Management/dp/0837603005 . PM if interested.

Sixto
98 E320s sedan and wagon

alright folks,

I just wanted to report back for anyone reading this thread in the future...

I replaced the fuel accumulator and did not get much of a result. Car still starts rough and has some hesitations.

So I guess I'll need to bite the bullet and get a pressure test kit as I don't want to just throw money and parts at the system.

Go to youtube - type in:

CIS Mercedes fuel

Lots of videos - not all pertinent - but there might be something in the mix to help out.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"