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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22744
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My mercedes 300Sl is difficult to start when cold When it

Customer Question

My mercedes 300Sl is difficult to start when cold When it does start you need to leave it ticking over for about 3 minutes before you can give it any accelerator as otherwise the engine will cut out
Also Do you know where I can locate Wood Trim that is damaged just on the dashboard around the heater controls
Submitted: 3 years ago.
Category: Mercedes
Expert:  Shantal-Mod replied 3 years ago.
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Expert:  Matt replied 3 years ago.

its a mechanical injection system on this and there's a device called a warm-up regulator that is supposed to increase fuel pressure as the engine warms up


so check that this device is getting power

as for the wood trim

try the specialist breakers

Customer: replied 3 years ago.

Can you please be more specific.

In order for me to check if the regulator is getting power I need to know where this is located

Expert:  Matt replied 3 years ago.

the regulator sits in the engine bay

Customer: replied 3 years ago.

I have checked ad there is power coming to this. It is nearly impossible to start the car when cold but it is fine once it has been running for a while. If you switch it off once it is warm there is no problem in restarting the engine


Expert:  Matt replied 3 years ago.
Hello Tony

OK if there' s power to the regulator the next step is to measure feul pressure at the fuel distribution n unit

any fuel injection shop should be able to cope with this as the fuel pressure when the engine is cold should be 6.5 Bar when cold and drops to 4.7-5.2 bar with a warm engine

if its not this high then I'd suggest stripping the regulator down and cleaning it

The regulator is held to the engine by two hex bolts, and is held together by four flat-head-screwdriver bolts. Be careful! The unit contains several springs and other fragile components. Take it apart indoors in a clean environment where you can keep track of all the little pieces. When it comes apart, there are three metal pieces held together by two gaskets in a sort of sandwich. If your gaskets are ruined (hopefully not) you can replace them with that gasket maker stuff.

Once you have it apart into these pieces, you’ll need to remove the 10mm nut on the heating element and carefully bend the heating element out of the way by bending the two wires that attach to it. Now, use a small flathead screwdriver and remove the four bolts that hold down a circular diaphragm.

Once you have that taken apart, get out your carb cleaner and spray out the insides of the thing as best you can. Now, put it back together, making sure that everything goes back the same way it did before.