You can't afford to get snarky with the only knowledgeable person helping you.

A good scan tool will show if the ECU is released by the DAS box to run the car. The DAS or alarm system don't need reset, it is plug and play if the key matches the DAS and DAS matches the ECU. I've shuffled these 3 parts between cars and never had a problem. I've even gone so far as to put a 97 C280 and 97 C36 AMG ECU in my 97 SL320 and had zero starting issues. The fuel maps were all wrong but the car ran and drove.

Also, if the key / DAS / ECU are miss matched the engine will run for 3 seconds then shut down, you car isn't doing that.

There are usually CD manuals on E bay.

On my 97 C280 / SL320, the 50A ( is 40 A on my cars ) fuse on the K40 is for the electric air pump relay / motor on my cars and won't affect starting of the engine.

If there was a " short " you would have melted wires / fuses that have cleared. Calling this issue a short shows a fundamental lack of understanding of electrical systems. Couple this with the lack of a wiring diagram and this project is doomed to fail.

I appreciate the help but I do not appreciate the tone.

A short can very easily cause a low voltage issue especially if there is high resistance in the short. Remember that V=IR and the equations for series and parallel circuits. A short with a bad connection will cause a voltage drop and not melt wires. Think of how when you run too much load on a circuit the lights dim. There is either a voltage draw(could be a short) or the multi meeter is wrong when reading injector voltage but not when reading battery voltage.

Got it. It gets really frustrating on my end going through the same explanations over and over then you not having a wiring diagram. Dig around on e bay for a service manual CD. The electrical section is called ETM . A wiring diagram is critical.

You are speaking of a compound problem that , while possible, isn't common. In any event, get a wiring diagram. If e bay does not pan out, MB has a online manual service and All Data / Mitchel have consumer grade one car access for something like $ 30 per year.

Well I do appreciate any help I can get on the issue. This is something I'm working on in my free time and hopefully I'll have a bit more of that next week.

Correct. That's my understanding, so I don't think it is the immobilizer. Since it runs with starting fluid the issue seems to be fuel. I don't know how to interpret the 6V you measured on the injectors. If you are measuring the high side then I think it should be higher. If you are measuring the low (switched) side then I don't know how a multimeter wold interpret the PWM signal there. I think you would see a pulse. I would verify the fuel pump runs with the key on and measure the fuel pressure.

The security/ECU/immobilizer/fob/IR/chip issues in these cars are a nightmare however. Mostly they prevent the owner from using their own car. That is my experience anyway. Hopefully that is not your problem.

The 98 + cars with a " smart key " fob are the difficult ones, 97 is simple.