I recently was given a 1977 450 sl roadster fuel injection with about 80k miles on it from my grandpa. It seemed to be in good shape, as he took good care of it. However, on the trip home, two hours out of his house it stalled on the highway, and would start up after a few minutes of rest, but stall out quickly again. It mader a funny, light, airy hum tone when it was off after stalling. We had the car towed home and sent to a mechanic. The company did a bunch of work to improve the driving quality, and a new fuel pump, which was what the problem was found to be. However, after driving the car every other day or so after the repair, it stalled after only 15 minutes of driving. It made the same noise, and would start up again but stall ouot after rest. Any ideas?

 

It sounds as though your fuel pump is working if you're getting the hum from the back, so it could be the ignition control unit. These do sometimes have intermittent faults. You need to check if it has spark while it is actually in breakdown mode. If it is the ignition control unit, you should be able to find someone who can repair it for you. These are expensive to buy new. It is a silver box with two plugs on it, mounted on the LH inner Guard, sort of near the coil. Follow the small wire from the distributor, (which should be green) if you can't find it.

It is also possible that the green wire from the distributor has a problem with it though, but this is rare.

 

I found the box, with wires intact. How exactly am I supposed to check for a spark, though? The box doesn't seem to have any openings.

 

I suggest you get a mechanic involved to check this. The voltages can be in excess of 20,000 volts and can give quite a kick.

 

OK, I will. Are there any other suggestions that I can give the mechanic regarding my situation?

 

Just to make sure that your fuel pump is cutting in and you have fuel pressure.

Also when he checks it, The green wire should have about 600-800 ohms resistance, and should not earth.

Good luck