'71 280SL won't stay running

[ryanpe56]

Hi everyone,

I am a domestic car rebuilder for the past 30 yrs and only have experience in carbureted vehicles. I now have this customers SL that has been sitting for 15 yrs. I replaced the fuel tank, rebuilt the fuel pump (Mercedes Source kit),drained all fluids, installed all new hoses and filters, C&M Hyd. power steering pump, new water pump, new crankshaft seal, cleaned and blew out every steel fluid carrying line, installed a Pertronix module, new cap, rotor, plugs, battery. I initially tested the pumps rack and it had good movement. I have refilled the SL with new trans fluid, engine oil, power steering, coolant, 91 octane.I pulled the cold start solenoids and cleaned the contacts and tested the gas valve operation while cranking and this circuit works as designed. So the engine will start up immediately but runs for only a few seconds. I suspect that it consumes the cold start fuel spray and then dies.  I checked #6 injector line and its dry. There was so much varnish in the fuel pump that actually had to scrape it out, not just flush it out. The injector pump I flushed as best as I could with carb cleaner prior to reassembly and at that time the rack was still very free and smooth. However, now i can't shift the rack. I suspect it picked up some debris or varnish and has locked up. I will take any suggestions. Do I have to relieve the fuel pressure before I try to move the rack?  Thank you all in advance!!

[roymil]

Sounds like you've done a lot of the right stuff.   You are correct that the injector pump rack needs to be free.   Given that you said it was free at some point in your cleaning then agree something is jamming it up.   Remember also, that even if the rack is free, the individual pistons can get hung up and frozen too.   There are some threads on this site about how to free them but just be careful not to damage them.  I used solvents, and light taps with a hardwood dowel to gradually work them free.  Another thing I didnt see you mention is if you had checked the injectors themselves.  They have mechanical pressure activated valves than can easily be contaminated and clog the jets.  If the car was stored that long with fuel in the lines then I would pull all the injectors and soak them in solvent quite a while.  I eventually had to replace all of mine even once they were clean because they were not spraying properly due to corrosion.   I determined that from checking them on a bench test setup where you can see the spray pattern.   Good luck!

[ryanpe56]

Thx! It was suggested to meet wait until I run the engine for a while before I pull the injectors to ensure that all the fuel had been flushed through the system and then clean the injectors. However, I have really not reached that point yet. Can I do this piston flush with the pump still on the engine? I've seen pictures on this forum that look like they flushed them out while still on the engine or wold it be better to remove the entire unit and clean it on my bench?

[roymil]

I was able to free the pistons and rack while the pump was still on the engine using lots of solvent and a pan underneath to catch the mess.  With the metal cylinder lines and the seals removed you should see the pistons move when hand cranking the engine and it becomes pretty obvious if one of them gets stuck at the top of it's travel or if it isn't twisting with rack movement.  In my case one or two would intermittently hang up and freeze the rack.  It just took time and gentle persuasion to finally get them all moving smooth.   

I cant imagine any downside to pulling the injectors and soaking them, along with their feed lines.  If yours are like mine after sitting for 18years you will find a varnish like goo sitting in the lines and inside the injector input ports.  That all has to come out obviously.  you should be able to get them clear enough to at least run the engine.  After that, in my case I could never get all the cylinders burning evenly until I replaced all the old injectors.   They didn't have consistent pop off pressures and some dripped instead of spraying.  I believe this was due to corrosion inside because I could see pitted metal surfaces on the input port and around the spray port. 

[roymil]

The engine recovery plan after so much time is really simple.   If it's made of metal, remove and clean it.  If it isn't made of metal, replace it.  If you think you've found an exception to that rule, let me know because I sure didnt. ;-)

[rwmastel]

Some people have little ultrasonic cleaners for carbs, this is useful for fuel injectors as well.  No reason to wait to determine if the injectors are good.

There is a valve(?) in the injection pump where excess fuel exits to return back to the fuel tank.  Make sure that's working to allow the whole fuel circuit to work.  Best tests for electric fuel pump are to measure fuel pressure at the port off the main fuel filter housing (or at the cold start injector on the intake manifold), and to measure fuel flow rate at the return line to the fuel tank.

Is this a 230SL with the R11 fuel injection pump?  It has its own oil reservoir and dip stick.  Machine tolerance between parts inside the fuel injection pump are extremely tight/precise.  Proceed with care if messing with the internal plungers, seals, check valves, etc.

[mdsalemi]

...I cant imagine any downside to pulling the injectors and soaking them, along with their feed lines.  If yours are like mine after sitting for 18years you will find a varnish like goo sitting in the lines and inside the injector input ports...

The OP RyanPE56 mentioned Mercedessource, and Kent Bergsma has a kit for testing the fuel injectors I believe. Others have made something similar, and Jim Villers brought one to the Charlottesville event back in 2017. At that time people were pulling the injectors from their rough or not as smooth as they liked cars, and Jim was testing the injectors. The results were generally very simple. Good injectors with a good uniform spray; marginal injectors that became good once that pressure behind the pump tester was pushing cleaner through; and bad injectors that simple could not easily be cleaned. I think the protocol for those is the ultrasonic bath/soaking and test them again on the pressure pump tester. I think this pump testing setup is relatively inexpensive compared to professional service and or injector replacement thus may be well worth the money.

Roy, I love your statement: If it's made of metal, remove and clean it.  If it isn't made of metal, replace it.  I issued a similar statement about my car during its restoration, to the restorer: if it needs to be replaced, replace it. If you THINK it may need replacement, than that really means it does, and replace it. (sometimes replacement meant restoration but you get the idea...)