86 300e with 250K miles on it. I was on the sprain pkwy going north to upstate new york when suddenly there was a hiss and wierd knocking sound. I started pulling over and just as I did the car died. I checked the spark plugs, voltage regulator - brushes are fine...Couldnt visually see any wires disconnected, tested the battery it was fully charged but the thing jsut wouldnt start at all...it would turn and die. Had to get a tow truck (my first two experience ever...it was devastating) and he towed me to some random garage where the guy is going to wake up and find my car in his driveway...

Any ideas what the problem could be ? So I know what to expect tomorrow when i speak to this guy tomorrow. I hope this doesnt cost me a bundle.
I towed it here Y and J auto, 79Mc lean ave, yonkers, ny. Thanks.

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***SAMI*****
1986 300E 240K
1999 Mitsubishi Spyder GS 60K

Your motor needs three things in order to start and run:

1. Spark, easily checked by using a spark checker to replace spark plug.

2. Fuel

3. Compression, lack of this would signal serious problems, but I doubt this happened.

If I had to guess, because the car died suddenly and the engine still turns, you lack either spark or fuel.

One thing to check, since you mentioned a hissing sound, is for a large vacumm leak, the plastic line the supplies vacumm to the brake booster can break and result in a large enough vacumm leak so that the car will not start due to a leaned out fuel mixture. The knocking sound may have been detonation caused by the lean fuel mixture. The line takes a few minutes to change and costs around $50.00 or so. Most MB dealers stock the line or can get it overnight, you will need your vin number to order it.

Make sure you put a dollar limit on the work order before you sign it, say for a couple of hundred. That way the mechanic doesn't have a blank check for repairs without your approval.

sami, if the garage where your car was towed isn't trained to work on MB automobiles I would call 1-800-FOR-MERC and have MB Roadside Assistance evaluate your problem. If it's a simple vacuum leak the tech will probably use some duck tape to temporarily repair the leak so you can drive to a shop to replace a hose. In the future call them when you're stranded along the highway.

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Fred Hoelzle

I would first start with checking the fuel pumps. Turn the switch to the #2 position which is when the dash lights come on and listen for the hum of the fuel pumps. You should hear the fuel pumps humming and the sound will come from the rear under the car, below the passenger seat. No humming means fuel pumps may be shot . If there is a humming then fuel pumps may either be creating pressure for the injectors and the fuel filter may be clog. Or the problem could be that the fuel pumps are create pressure but not enough for injectors to fire. Also check your OVP relay. Keep us posted.

Didn't something like this happen to several people and it ended up being the Crank Position Sensor?
Also something similar happened to another guy but it was his rotor inside the distributer cap that had cracked and broken off.

fuel pump relay. I keep spares in the glove compartment of my 87 300e and 88 300ce.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)