HELP! FUEL INJECTION

[Bwedd84]

Hello all

I just inherited a beautiful 1 owner 67 Mercedes 230SL that a family member owned since new.  I am a classic car guy but all my cars are 1940s american cars and I'm stumped on fuel injection.

I drove the car the last couple weekends and feel like the last drive I took was tad rough idle at stop lights.   I got home and parked it for a week and went to start it today and it cranks but won't start.  First thing I did was get my volt meter and check the power to coil, then made sure the spark plug has spark and we are good with a nice spark.   The car turns over great and has perfect compression.   So spark and compression are solid.   All that was left is fuel.   The electric fuel pump is working and getting fuel to the fuel injection block.   I unscrewed one of the injectors and with cranking and pressing throttle no fuel comes out.   I have no idea what goes on inside that fuel I jection system other than assuming there is a pump?   

Is there any relay? Anything easy I could check before assuming that entire Bosch fuel injection system needs to come out for service?  Not sure exactly what else to check or mess with and it was driving so well and now nothing.  Thank you for your time and advice. 

[Cees Klumper]

Welcome and the car looks very nice. It is strange that the car was running fine just recently, but now no fuel is getting to the injectors. Did it sit for a long time before you started driving it? It is possible the fuel pump lacks the 'oomph' needed in terms of pressure and volume. There are specifications for both in our technical manual, but you may need to become a paying ('full') member to be able to access it. There is also an excellent Haynes manual covering our cars. Best of luck troubleshooting what is probably not a major issue. I would not suggest taking the injection pump out for rebuild before doing some more basic diagnosing.

[Kevkeller]

Try a little starting fluid in the intake. See if it fires. If it does it’s probably your gas. Maybe it’s bad gas?

Kevin

Edit: I thought I read there was gas coming out of the injector line. After rereading it is not.

[MikeSimon]

The fuel injection pump is a mechanical six-piston pump. It is strange that you have fuel all the way to that pump, indicating that the electrical pump at the tank is functional and there is no fuel coming out of the lines to the injector. Once the FI pump gets fuel, it should put some out. Most fuel issues that prevent the car from running are in the system before that pump.

[rwmastel]

... but now no fuel is getting to the injectors.

The ONE injector tested.  I recommend testing them all.

What do all the spark plugs look like?

Test the cold start valve on the intake manifold to ensure it is adding fuel for startup.

Test fuel pressure by connecting a guage (assuming you have the metric adapter) at the port on top of the main fuel filter housing.

Test fuel flow rate at the return line at the fuel tank.

Let us know your results.

FYI, We've been online 20 years, so make use of the search feature.  You're not dealing with a unique issue.

[ctaylor738]

Run a jumper from battery positive long enough to reach the cold start valve.  Disconnect the wire to the top of the valve. Have an assistant crank the starter while you touch the jumper for a second to the valve's terminal.  If the engine at least fires, the problem lis likely the cold start valve or its electrics.

Good luck,

CT

[Bwedd84]

Thank you all for the replies!  I thought I would get an email when someone replied but I guess that is not the case.

So I went out and took of the side plate to the injector pump and set my camera up so I could make sure the pistons inside were moving.  I cranked the key and IT FIRED!  it has been working great ever sense.   I wondered if something was weird with the cold start valve.   

The inside of the injector pump looks very nice/new/clean.   

Can someone explain to me what the cold start valve does?  If it's bad will the car not start even if everything else is working?  The electric fuel pump definitely works because I am used to 3lbs of pressure on my 1940 flathead engines and this fuel shoots out like a fire hose.   

I appreciate the help.   The spark plugs look great, car runs smooth and great, everything seems perfect at the moment.  I would just like to know more about the cold start valve or any relay that is associated with the fuel injection system since I don't understand exactly how it works or what tells it to kick on etc.

One other thing...... I would like to degrease and pressure wash the engine bay and clean everything up.   Is there parts I should not get wet? 

Thank you. 

[ctaylor738]

See the long Starting Aids post for details on how the cold starting system works along with the full enrich solenoid.

Some cars start fine with the valve disconnected. 

Others need the valve activated for a cold or hot start.

CT

[Peter van Es]

Thank you all for the replies!  I thought I would get an email when someone replied but I guess that is not the case.

You can... see screenshot on how to do this...

If you always want to be notified... you can set the following option on your Profile/Modify Profile/Notifications (see second attachment)