I have a 1992 W140 that won't start. Well it does, but it won't hold.

Basically, when I have enough battery juice, I could crank the engine, it will hold for 3 seconds by flooring the fuel pedal, then it die. Alternator doesn't work so well. So I have to jump start, charge it for 10 minutes, and crank the engine again. It died again every time.

What happened was this: I was running on empty, probably with about 1 gallon of Diesel in the tank then I put about 2 gallons of GASOLINE in it. Stupid mindless me. I ran for about 4 long blocks, engine knocks funny, I realize what I did, so I turn around to go back to the gas station. Engine died when I got there. I decided to fill up Diesel, probably 18 another gallons. Car ran fine. Phew I thought. Then a day (or two) later, another stupid move of mine: I was on a highway driving with a bit of uphill incline when I had to push the pedal hard at 70 MPH, suddenly the engine stop. Pulled over. Changed fuel filters think they might have clogged. Nothing seems of a suspect. Then car won't hold afterwards. Started fine but died after a few seconds.

Squeaking sounds coming from the engine when it turned at low RPM. But at high RPM it sounded ok. I had a brilliant mind from this forum who happens to be close by looking at this problematic car and he could not figure out what the problem is. We did check and saw that the fuel was going out of the injectors' delivery valves when it cranks, not sure if it's the right amount, and the squeaking was not due to the belt.

Unfortunately, the alternator doesn't charge so well, every time I crank, it takes about 5-10 minutes to recharge the battery from another car with jump start cable so I could start the engine again.

I sounded to me:
1/Battery drained completely due to bad Alternator so car died on battery juice be drained of due to the crankings. The Brilliant Mind told me as long as the engine start it should sustain without alternator and battery because everything is mechanical at that point. (this is when I speculate that its the Alternator that have broken and caused the car to stall everything.

or
2/ Fuel isn't delivered enough due to clogging
3/Something is holding back the engine, causing the squeaking.

Please advise. Thanks, and regards,
Californian.

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1992 300SD, 290K miles.