I've got a 1994 320e wagon which wouldn't start. I charged the battery, and it started & drove fine for a day. The next day, the battery was dead. I replaced the battery, but the engine still wouldn't start. I suspect a fuel system problem.

There is a continuous faint, high-pitched humming noise that seems to originate from the electronic fuel injection system (HFM). There's also a lower pitched rhythmic kind of ticking/purring sound which seems to come from the same area.

I manually pulled the throttle cable, and both the humming and ticking noises stopped. I'm going to leave the battery connected overnight to see if the battery drains again.

I've checked to see if there were any bare wires touching metal. I found some bare wires, but none touching metal and apparently unrelated to the problem. I'm stumped and would appreciate any ideas/suggestions for pinpointing or solving the problem.

Is the noise from the throttle body area?

This is electric motor driven and could be the source of the noise.

Also, do a search for "Mercedes bio degradable wiring insulation" Cars from this era had insulation that crumbled. The was mostly the engine harness, good news is that the harness can be changed in an hour or so, some updated used ones pop up in the parts section of this forum.

the previous post is correct, the harnesses degrade badly. any bare wire you see means more you can't see. the throttle body harness has the same wire that's crap, just tougher outer insulation.

give it to a shop and they'll tell you put harnesses on it and then we can see if there's a real problem. stray voltage in harnesses you can't see make for strange issues out of the blue. good luck, chuck.

I bought this car used knowing about the terrible wiring, the previous owner had the harness replaced to the tune of $1800, still im finding cracked insulation all over the place..... Bad wiring, terrible windshield wiper design, the worst air con system ive ever seen. this car is crap! Im gonna buy something reliable, maybe an old English car or a Yugo

Hey, a 1956 Fiat 500 would be it. Just need a shoe horn to get in, ha, ha. Also, make sure it comes from California and never was operated anywhere else.

Seriously,
If the engine wiring harness was replaced, doesn't mean that the Throttle Body wiring is good. Throttle Bodies made before 1996 are most likely equipped with bad wiring and can short out things you rather would not have shorted out. I bought a 95 E320 Sedan, with bare wires, I mean absolutely no insulation at the throttle body. Engine Harness was replaced with a 2002 updated version. The bare wires on the throttle body, actually took out the e-gas computer. To see the extend of the damage, you'll have to cut the sheath from the Throttle boddy and have peek inside. Or, much tougher, if you can see the manufacturing date, you can guess by date. There are other spots in wiring, but the previous are the most important.

__________________
Mostly, I don't know notin, I just know where to look.
I am looking back, to over 30 years in Electronics Design.
Electrons don't care if they move in a car, computer or relay!

95 W124 E320 M104.992 - Because, I love to repair, naaaah!
Over 221,000 Miles
Cheers,
Norbert

Yes i guess your right, its more fishing than i want to do but if i have to take it apart wire by wire i will. Ill fix this SOB if it kills me, then find someone i dont like and see if they want a free car! Its pretty bad when my old ford truck with 260000 miles is more reliable than a MB with 120000, this car is every bit as problematic as my 1987 range rover