W113 280SL shuts off

[Sardalani]

Hello, everyone. I’m posting this on behalf of my father, as he has a Horizon Blue 1968 280SL. Recently we tried turning it on and the car turns over but will only stay on if your foot is on the gas pedal. If you take your foot off the gas pedal, it hesitates to stay on and then quickly shuts off. This is all happening in park, of course. Has anyone had a similar issue? Or possibly know the cause? Thank you in advance.

[baon3h]

Could be one of many things. I had a similar issue and the root cause was a vacuum leak coming from the brake booster. Inspect the vacuum line that runs from the intake manifold to the brake booster for leaks/cracks. To make sure it's a vacuum leak, unplug the line on the manifold side and plug the hole.

What is the RPM when idling (no foot on pedal)? Should be between 750 and 800 when warm, 1000 when cold.

[Sardalani]

Hmm, I haven't heard that one before, but I will definitely take a look. I am honestly not sure about the idle, because I have to press the gas pedal down, just to keep it alive. If I let go of it, it will stay on for a couple of seconds and then quickly die. So far, I have replaced the fuel filter and drained the old gas and poured fresh gas with techron. The car has been sitting for a few years.

[Vander]

To me it sounds like a fuel delivery issue. If you drained the old gas, I am assuming you cleaned the in-tank drain plug screen? There is a screen inside the fuel pump, follow the hose from the tank to the pump. Undo the hose at the pump, buzz off the fitting which I believe is a 27mm. Then you will see the screen, inspect clean and re-install.

[baon3h]

How long has the car been sitting for?

[Sardalani]

Fuel tank was drained and yes I replaced the in tank filter as well as the fuel filter.

[Sardalani]

It’s been a few years. Stored in a garage. Before starting it, we put a new battery, drained the old fuel and put fresh fuel, in tank filter and fuel filter. I was thinking of doing a basic tuneup next (plugs, wires etc) but the car starts, so leads me to believe it’s not an ignition issue.

[Vander]

It’s been a few years. Stored in a garage. Before starting it, we put a new battery, drained the old fuel and put fresh fuel, in tank filter and fuel filter. I was thinking of doing a basic tuneup next (plugs, wires etc) but the car starts, so leads me to believe it’s not an ignition issue.

Since you already have done many other fuel system items, clean the screen inside the fuel pump first.

[Sardalani]

Since you already have done many other fuel system items, clean the screen inside the fuel pump first.

Is there a separate screen for the fuel pump? Or are you referring to the in tank screen/filter? Because that has been done.

[Vander]

Is there a separate screen for the fuel pump? Or are you referring to the in tank screen/filter? Because that has been done.

Yes, there is a separate screen INSIDE the fuel pump. Copied from my previous comment above...

"There is a screen inside the fuel pump, follow the hose from the tank to the pump. Undo the hose at the pump, buzz off the fitting which I believe is a 27mm. Then you will see the screen, inspect, clean and re-install."

[Sardalani]

Yes, there is a separate screen INSIDE the fuel pump. Copied from my previous comment above...

"There is a screen inside the fuel pump, follow the hose from the tank to the pump. Undo the hose at the pump, buzz off the fitting which I believe is a 27mm. Then you will see the screen, inspect, clean and re-install."

I was not aware there was a screen for the fuel pump. I will inspect that this week and see what its condition is. Thank you!

[rwmastel]

When replacing the main fuel filter by the engine, was there much rust in the canister?  When I bought my car, the canister was 1/4 full of rust.

If that screen is not the problem, the electric pump itself might be.  Take the rubber return line going back into the tank from the engine and point it into a jar.  Of course, plug the tank connection from leaking.  Turn ignition on (not the starter!) for 15 seconds and measure the amount of fuel pushed through the entire system.  This checks flow rate of pump, and checks for restrictions in the system.

After this, there's a fuel pressure test.