Problems with starting my 420 SE (W126)
 

Hi there,

Cold or warm, I often experience some difficulties starting the engine: at the first crank it's revs up and immediately drops dead.
When I try again it won't start anymore. After insisting serveral minutes, it starts running again, quite normally.

For your information:
-Battery is in good condition
-enough fuel is in the reservoir
-fuel smell while engine's running
-irregular idling speed

What could this be: a mechanical or electronical problem...??

Do you have any ideas for me, please.

Thanks in advance,
Rémy K.

Possibly a fuel pump about to go out. I hear they have intermittent no start before they fail. It's a real guessing game without taking it in to a shop while you are having the problem.

O2 sensor or Fuel Lines
 

What year is the car? Is it an SE or SEL?

If it is an SEL, it could be the O2 sensor. I experienced a similar problem and replacing the o2 sensor which solved the problems of difficult start, stall after start, and rough cold idle.

It is odd that you smell fuel when the car is running. There should be no fuel smell in the passenger or engine compartments. I recently smelled fuel in my 1989 420 SEL. The problem was the hose from the cooler to the fuel distributor. It was leaking where rubber hose meets the metal fitting. The fuel was not dripping. I found it by using new paper towel all around the hose and then smelling them. There just a slight film of fuel on the fitting and hose, which evporated in the hot engine compartment.

I recommend checking all the fuel lines for a leak.

Fuel smell and rough idle is typical of a faulty EHA.

on a post earlier
 

today they solved the same problem on a 300e with a new check valve at the fuel pump. i have a similar prob on my 84 500sec and i am going to try the check valve thing on it.

tom w

problems getting my 420 SE ('89) started
 

Hi JDC 1244,

being a Dutchman, could you please explain to me what is a EHA...

thanks!

Rémy K.

The EHA/Fuel Distributor may be dirty, leaking, or not getting current:

http://www.thebenzbin.com/mercedes-gas-smell.html

I think you have two unrelated problems. I think Tom is right about the fuel pump check valve. The fuel smell which I don't think has anything to do with the starting problem could be the EHA or other hose leaking.

Cigar
Did you replace the o2 sensor or did a shop do it? I do not see how an o2 sensor can affect a cold start since the car is in open loop and doesn't even know the o2 sensor exists.

Peter

Shop
 

An independent highly experienced shop replaced the O2 sensor.