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The car runs for five seconds then stalls

1247 Views 30 Replies 5 Participants Last post by  MBGraham
I have a 1974 Mercedes 450 SL that runs for exactly 2 to 5 seconds and then stalls consistently… Any thoughts?
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When did this start happening?

Did you do any work on car before?

Could be so many things so some history would help.

Maybe for a start, ensure you have 30psig of fuel pressure.

Then see if car keeps running if you (carefully) spray fuel into the intake once it gets started.

This might tell you if it is a fuel supply problem.
Sounds like you are quite capable of doing what may be needed.

Check the stickies (EGV107) under sections 07.4 and 07.5. In particular,
the Comprehensive guide posted by Proctologist (who we don't see here lately!)

The on-line FSM hosted by oncebitter (Open under engine type)

Bosch EFI training manual

Maybe think about adding Pertronix as points replacement or both points and switchgear (ign module)
However, thank you for the Bosch injection link, however, the FSM link is of great interest to me however appears to be broken.
Sorry about that. I fixed the link in previous post. But here it is again anyway: Model 107 Maintenance Manual Index

Have you checked the fuel flow? You may know this, but some new owners have hooked up the fuel lines incorrectly. The supply line from the pump finds it's way to the front of the fuel rails (diferent cars have different rails, but in principle they are all like this) From there, flow splits and passes to rear of rails where they recombine through Fuel Pressure regulator . The fuel passes through a pressure damper and then flows back to tank.

If this is connected correctly, you might measure the fuel flow you get on the line leaving the damper. (You will have to jumper relay, or provide 12V to pump directly. You should get 2L/min (1L/30 sec is the spec)

While you have that line disconnected, make sure you can blow through the return line to the tank (there is a nozzle inside tank that gets clogged)

If you are not getting flow, common problem for cars that have been sitting, is sludge in tank, clogged tank screen and plugged up fuel filter. It could be that you just get enough fuel to start the car, but not to keep it running.
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Do you mean that owners inadvertently connect the supply line to the dampener, Which passes through the fuel regulator then on through the rest of the rail?
Yes, you would be surprised how many times that has happened here! Some thought it should be like that. Others inadvertently connected the hoses that way because at least on some cars, they are close to each other.

Well, at least the car is starting and running. Unfortunately, I am receiving absolutely no contribution from cylinders 1,2,5 or 8. The other four cylinders are running perfectly with even contributions. Each of the eight of the cylinders has 150 psi and new injectors.
That is odd. The injectors fire in pairs 1&5, 4&8, 6&3, 7&2. So if 7 fires, so should 2. Same if 4 fires, so should 8.

Make sure you have the numbering correct and that the injector wires are going to the correct injector (it is easy to reverse some of them. If you find an error and it is injector groups that are not firing, then check trigger points. First just rotate and using ohmmeter make sure each contact opens and closes.

Otherwise, check continuity of injectors back at the ECU plug under the dash. If you disconnect one injector bank (left or right) and measure resistance between terminals 11 (ground) and pins 3 to 6 in turn, the injectors should each measure about 2.5ohms. Then do the other bank. (If you leave injectors connected, you should read about 1.25ohms for the pair in parallel. This will tell you whether the harness from ecu to injectors and the injectors are OK.
So sounds like you have bad new injectors? Did you do the resistance check?
That may not be correct. EPC says the top hat seal for an early Djet like my 72 is part # 1160780473


By the way, these are the only seals. There is a rubber clamping bung up above, but that is not a seal.

Hopefully the injectors all have a plastic pintle seal fitted over the metal tip. The above top hat seals are designed to have these in place.

By the way, how are you checking to see that an injector is firing or a cylinder is functioning?
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