E320 Starting Problem

I have a 96 E320 that sometimes starts fine, then other times cranks but doesn't start. Some days it takes 5 or 6 tries, then finally starts, other
days not at all. I'll come back 2 days later and it fires up no problem. My mechanic said he couldn't duplicate the problem, and I left it there for 2 weeks. I have replaced the crankshaft positioning censor, the fuel filter, plugs, wires. Am thinking about going to the dealer, and they told me it would be at least $200 just to see if they can figure out the problem. Any ideas out there before I spend a bunch of $$? Thanks
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Does the no start always occur when the engine is cold? Or is it intermittent?
When the motor does start, does it start quickly and otherwise normally?
If this were my car, and I own a '97 E320, I would strongly suspect the fuel pump relay - it's an ON OFF switch for the electric fuel pump.
When you turn the key to ON do you ALWAYS hear the fuel pump run for about a second prior to you cranking the engine?
Listen carefully, it's your money; if no brief hum is heard the fuel pump relay becomes the #1 suspect.
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When it starts, it somethimes starts quickly, other times a few seconds, and sometimes I can try 4 or 5 times and then it starts. One thing I do hear is some kind of clunk in the engine compartment just before it starts.
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Steve wrote: ...

This clunk noise is not the fuel pump working: the fuel pump makes a sound like an eletric motor, very discret when it works. It's at the back side of the car, at the bottom of the fuel reservatory, down the right rear door. You can hear it when the key is at that position right before the cranck stage - when all the lights at the dashboard comes. Let your car be inspected by a competent indy to diagnose this clunk noise. HTH, RSalles
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I can try 4 or 5 times and then it starts.
Do you mean it cranks but doesn't start OR
Turn the key and ..... silence????
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Always cranks. As for the fuel pump relay, I listen for it every time I try to start it. And I hear it, a brief hum, and sometimes it starts and sometimes it doesn't, so I would think to rule out the relay, I would think. Happened twice today, cranked it over about 3-4 times and it eventually started, but something isn't right.
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If you have trouble starting the car after hot engine and within like 30 minutes... then you got fuel pressure leak... usually a fuel injector is leaking. TG had this problem too.
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My wife had owned a 1990 300CE which had the same engine as yours. Her car would often stall within a couple of miles when stopping for stop sign. This was within a few miles from the house. Only seemed to happen for her in the morning, on the way to work. The car would begin to shake violently and then stall. Restarting was hit or miss. There was never an issue with the initial start-up in the garage.
I once ran the car at high speed on an interstate, during this period. When I came to a stop, at the exit ramp, the car shook and stalled. It took me close to an hour to restart. It seemed to want to start, but wouldn't. The car was dropped at an independent MB shop that in the past has done excellent work. They could not find the problem, it didn't stall.
After the problem persistent, the car was taken to the dealer, which was NO HELP. It actually stalled on dealer mechanics in town and needed to be towed. The dealer couldn't find the problem, essentially gave up.
It wasn't until the car went to another independent MB shop for a water pump replacement that the problem was fixed. At least it never happened again. I had mentioned the stalling problem to them at the time the car was dropped at the shop for the water pump. The plugs were real bad and were replaced. But, I never heard if they found something else. We later traded the car but never had a stalling problem again, for several years.
I recently bought a 1991, 300SL, again with the same engine. It has about 97,000 miles. The previous owner mentioned a starting problem with the car. It was taken to the shop that repaired our 300CE. They found no problem after having the cars for several weeks in which the parts man drove the car daily. This car has a manual transmission. The clutch must be depressed for the starter to run. After not being able to diagnose the problem, the shop is assuming the clutch was not being fully depressed when the problem occurred.
A couple of weeks ago, I had a problem starting the 300SL. It is garaged. I didn't have time to spend trying to get it running, so it sat for a day. The next day, I had to crank the engine several times, long duration, before it finally ran. No problem since, but I'm not confident the problem won't return. I may have depressed the gas peddle the day it won't start and maybe flooded it, was a very damp day. But that is likely a long shot, because the way the car did start, was when I just held the gas peddle to the floor and cranked until the car started.
Good Luck,
John
PS. The mechanics in the independent shops had all worked for the local MB dealer or other MB shops, so they are familiar with the brand.
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Your problem with hard long cold starting is because the engine temperature sensor is not working correctly... it didn't register proper temperature that the computer didn't know the car was full cold... therefore did not engage fuel enrichment to start up the car.
I always wanted one of those R129 300SL or the SL320... I prefer the 5 speed auto... but manual is good too!
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Tiger Thanks, I'm making copies of all these notes in the event the problem returns.
The 5 speed is fun to drive as I always liked to shift going back to the '60s. Eventually I will grow-up but trying to delay the inevitable.
John

temperature
speed
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Thanks for all who replied. It's not a hot or cold problem. It can be the first start of the day or trying to get out of a parking lot after 10 minutes. So I'll try to listen for the fuel pump relay that TG suggested.
I looked at old records from previous owner, and they had the crank positioning sensor and the neutral safety switch replaced. Both were a result of not starting. Another question.. are you suppose to be able to put the car in neutral and start the car? I can start it in neutral.
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If the engine cranks and starts in N consistently, but not P, then the problem is in the interlock or the neutral safety switch.
WE thought there was an engine problem!
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