'69 Starts then dies when warm

[John Ragan]

Hey all. New here to the site. I'm currently working on a '69 280 SL. Customer concern is that the vehicle starts fine, runs fine then dies after a while. Customer drives approx. 30 km before vehicle dies. I had it idling in my shop for approx. 15 min then it dies and wont start again. Vehicle sat for a year in storage before this started happening. Fuel smells ok. I have read some about the WRD sticking and causing this issue but I'm unsure its the cause. During warm up, I can hear air flow entering the air filter on the WRD, as the engine warms up, the airflow dissipates. Could it still be the WRD or does it sound like its working properly?

[Bonnyboy]

Sounds like rust settling in the tank and plugging up the outlet or a bad fuel pump.   Check the website for "flower pot" and rust in fuel tank.   Clean the tank and see if that helps.

Good luck and be aware the gas comes out of the tank in a real hurry if you remove the bung.

[cattledog]

Maybe you could rig up a jug with clean fuel in it and feed the fuel pump with it, to rule out the fuel tank as a problem.

Setting up a fuel pressure gauge in line, on the outlet side of the fuel pump (ideally after the fuel filter) might provide some insight too.

Maybe a clogged fuel filter?   

[Jonny B]

Rust and junk in the fuel is a prime suspect, remember there are three fuel filters: one in the tank, one at the pump inlet and the cartridge type at the engine.

Lots of information about this particular issue.

Good suggestion by BonnyBoy on using "Flower pot" (or flowerpot) as a search item.

[John Ragan]

Thanks guys! Ill check it out when I have it back in the shop and let you know the outcome.

[Iconic]

Maybe you could rig up a jug with clean fuel in it and feed the fuel pump with it, to rule out the fuel tank as a problem.
Setting up a fuel pressure gauge in line, on the outlet side of the fuel pump (ideally after the fuel filter) might provide some insight too.
Maybe a clogged fuel filter?

cattledog,
You would need a very large jug. The fuel pump should be pumping 1 liter every 15 seconds, and the car doesn't die until 15 or 30 minutes of use. So you would need over 60 liters of clean fuel in the jug.

John Ragen,
Here is my opinion: Clogged return fuel line to tank. The fuel circulation is used to cool off the fuel injection pump. If the flow is impeded, the pump heats up and that is bad for fuel. Search out my several posts on the subject for more details. Or just measure the fuel returning to tank (right at the return tank line going into the tank). If flow is very low, either the fuel pump is bad or there is a restriction in the fuel line. I bet on the restriction.
Good luck and it sounds like you are a professional, but be careful with fuel.

[John Ragan]

Iconic, I have noticed that one of the rubber return fuel lines in the engine compartment is leaking.....it looks a bit swollen, so you may have something there!! I will look into it for sure. Thanks for your input.

[ja17]

John, install  a fuel pressure gauge a note what the pressure is when the problem occurs. Most likely a fuel delivery problem. Remove the fuel gauge sender in the trunk and inspect the condition of the fuel tank.

[John Ragan]

So I checked for flow at the return line at the fuel tank and found none. Blew out the return line from the hose after the pressure regulator and found decent air flow. re-checked and still no flow. Disconnected the line before the pressure regulator and found no flow.... should there be flow right away? Could there be a blockage in the mechanical pump?

[John Ragan]

I connected a pressure gage where the csi port is before the mechanical fuel pump and am getting 2 psi? vehicles running with it connected....am I missing something here???

[John Ragan]

OK. So the pressure went up to 8psi with the vehicle running, seemed to be running well for a good chunk of time. Thought that I may have cleared the blockage and thus we have good flow again. Shut the vehicle off to disconnect the pressure gage and re-connect the csv line. Tried to re-start it and no go Im going for lunch......

[John Ragan]

Figured it out.... So when the vehicle was cold, the CSV was supplying fuel to the engine, there was little pressure at the mechanical pump (max 8psi). Once the vehicle warmed up and the CSV shut off, the vehicle would stall. I jumped the CSV after the vehicle stalled and found the vehicle to start once again, then stall once I deactivated the valve. I checked fuel pressure and flow at the pump directly and found less then 5 psi and approx. 200ml in 15 seconds. Supplied power from an outside power source to the pump to rule out poor wiring or connections and found the same result. It needs a pump. Now the current pump is a small oem pump. According to my parts dept, it requires a large pump. Nether of which are available from MB Germany anymore. I guess Ill have to call the Classic center on Monday. Thanks for all the help everyone.

[Iconic]

Did you check flow and pressure right off the electric fuel pump?
If not, then your pump might be good and there might be a restriction as I originally guessed.
If the pressure and flow is good right off the pump, then you don't have to buy one .... which would be great !

[John Ragan]

Yes I did check the pressure\ flow right off the pump. I also disconnected the main fuel supply at the pump and found very good flow. I'm still planning on draining the fuel tank and looking for debris though as the fuel smells quite old. I have read that these pumps are re-buildable....is this an easy task? Would it be a better route for my customer? And is there an issue that the small pump is installed when the large pump is OEM?