intermittent no starting 420SEL - PeachParts Mercedes-Benz Forum

#1 11-01-2002, 12:52 PM

I have an 86 420SEL with 125K miles on it. Car has been running pretty close to perfect, but last night could not get thing to start at all.

Here's the history on the problem.

A few weeks ago, the starter would buzz (maybe whir is a better description) when I turned the key. Engine did not turn over at all. It seemed to be related to started the car after I had pumped the brake until the brake pedal would not give, though I would guess that this could have nothing to do with it. The car also ran fine once started.

This probably mysteriously went away...

Then, had problems started my car one day about a week ago. Woke up and moved my car so that someone could get out of the driveway and parked it on the curb and turned the car off. Came back 45 minutes later to go to work. Turned the key, engine was trying to turn over, but nothing. Next turn of the key... started fine. Car ran perfectly and started fine later in the day.

Then, week or two later...car would not start. Again, car was moved out of the driveway and then I came back to it a few mintues later. I turned the key and held for several seconds and the starter would try to turn the engine over, but nothing. Tried again. Nothing. Waited a few mintues, tried again, nothing. After a few rounds of this, car started right away. Ran great-- better than ever.

Same thing yesterday morning. Moved car from driveway. Car started. Went to work. Car would not start for several minutes. Then when it did, it was fine.

Around 4pm that day, went to start car, it hesitated, but started on the first turn of the key. Rough idle for a few seconds, but then car ran fine.

6:30pm. Car would not start at all and it still sits where I left it. The engine tries to engage but it seems like its stalling out right away. Giving gas doesn't seem to help. Not sure if this makes a difference, but this time I parked on a small (very small) incline, with the car pointing up.

The day prior, it ran perfectly. Started car to move out of the driveway and it was fine. Started car a few minutes later. Fine. Started car around 4pm. Fine. Started car around 6pm. Fine. Started car around 8pm. Fine. Started car around 10pm. Fine. Started car around 2am. Fine. Started car around 6am. Fine. Car ran and started like it was brand new.

Without fail, if the car started it ran great.

Also, if anyone knows of a good shop in Boca Raton Florida, please let me know. I've heard of the one in Davie, but that's a hike and a half if you have to tow!!

stevebfl · #2 11-01-2002, 01:04 PM

My first guess would be the fuel pump relay. Try thumping it once next time it won't start. Try jumping the relay if it still won't start.

If that doesn't work you need to find whats missing. Your Dania connection would be worth the tow, if it comes to it. I presume you are talking about Raul at Ultimate Euro Repairs. In the wilderness that is S Florida, Raul is a gentleman.

#3 11-01-2002, 06:40 PM

I decided that whatever was wrong with it would be above my head, so I had my car towed to Ultimate Euro Repairs today. Seems like a nice guy. Lot's of old benz's out front made me feel confident that he knows what he's doing.

Still curious what people think about my car.

psfred · #4 11-02-2002, 11:54 AM

Three possibilities here:

1) No fuel. This means bad accumulator, bad fuel pump, bad fuel pump relay. Latter is most likely, so no fuel delivered.

2) No spark. This will have to be investigated on the car, can't help from here

3) Starter not engaging. If you get only a whirr or screech, the overrunning clutch is bad or the solenoild is getting weak and the starter gear isn't engaging the flywheel. If the engine won't rotate, it won't start....!

Peter

#5 11-03-2002, 04:12 AM

thanks for your comments.

pretty sure the starter is working fine. The whirring was a problem, but it apparently went away (have no clue why, but it did). Pretty sure the flywheel is enganging, at least it sounds like it.

No clue if I'm getting a good spark or not. If it makes a difference, the car runs great when it does start.

My guess is problems with the fuel system. Raul at Ultimate mentioned on the phone (based on what I told him) that it might be a problem with the pressure accumulator. Other posts on this website indicate that it might be a problem with the relay.

Could it be a problem with the fuel pump if the car runs fine once it starts?

We'll see, I guess.

Thanks again.

David

psfred · #6 11-03-2002, 08:37 AM

If the fuel pump relay isn't making good contact all the time, sometimes the fuel pump will run, and continue to run until you shut off, and sometimes it won't, in which case the car will either start and immediately die or not start.

MB relays are notorious for cracked solder connections as they age -- depending on the temp, phase of the moon, whether your rabbit's foot is sideways or not, etc. they will sometimes work and sometimes not.

Peter

#7 11-03-2002, 09:08 PM

So assuming it's the relay, how much should I expect to spend?

Thanks for your help.

David

#8 11-05-2002, 10:13 PM

nothing. car started fine and ran great. he is at a loss as to what the problem is. so am i.

#9 11-07-2002, 07:46 AM

I have the same problem sometimes. the car will whirl but it won't start, so what i usually do is put in in nuteral (N) and the car starts with no problem. Usually this happens when the car has been sitting for few hrs, so if anyone out there can help us please do. thanx

#10 11-07-2002, 08:06 AM

What does the transmission have to do with starting the car? Why would have the car in neutral make a difference?

At any rate, Raul @ Ultimate started the car Wednesday afternoon and it "finally" (I knew something was wrong but I'm not sure if I really want to say "finally") didn't start. He said it was "most likely" a problem with the fuel pump and fuel pump relay, so both are being replaced for a cost of $630. Is that fair?

David

#11 11-07-2002, 10:55 AM

Should not be hard to diagnose. Does the starter whip the engine over when it doesn't start? If the starter speed is up to snuff - then it has to be ignition or fuel. If the starter whips the engine over and it doen't start - turn the key on and listen for the buzz of the fuel pump in the back of the car. If it does not buzz - pump is failing or fuel pump relay is going bad or ignition switch is going. If starter does not whip motor over consistently and it whizzes or turns slowly then speed up - check battery cables or starter/ solenoid is going bad. If you logically diagnose your problem - the cure should not be too hard to figure out.
Just read you last post as problem being pump/or/relay. Pumps are about $300 and the fuel filter should be changed at the same time. If price includes relay and filter - it is very fair. Just had the same problem on the Porsche. Pump just clicked no start - just cranked. Disconnected voltage wires to pump and ran 12 volts direct to pump from spare battery to see if it would run - it did not - pump was seized. If it had run - problem would have been relay.

96C220 · #12 11-07-2002, 04:10 PM

Either One of Three things....

#1 Fuel pump relay about to die... There may be a cold solder joint, or other failure in the relay that will cause it to work intermittently, or finally quit.

#2 The actual fuel pump - it may be failing. But I would think that if the pump is failing hesitaton, or rough running due to inconsistent fuel pressure would be present. Does the car exhibit any of these symptoms?

#3 A ground somewhere may be loose, and making contact some of the time... This would lead to more of an intermittent no start / stalling in motion problem, as a bump in the road may loosen the ground and cause the fuel pump to stop pumping fuel while the car is running. Chances are this is not the case in your car because you have only mentioned intermittent starting issues.

You mentioned your tech recommended replacing both the relay and the pump. Did he test the pump by jumping the relay contacts to send 12V directly to the pump. - With the seat out or even with the first aid kit open you should be able to hear the pump.

The relay is a simple fix, and chances are will cure the problem. Especially if the pump tests out ok. Did the tech give you any reason for wanting to replace both? Or is this more of a preventative measure in case the fuel pump is on its way out anyway?

Also make sure the fuel filter is replaced when the pump is replaced.

Hope this helps,
George

psfred · #13 11-07-2002, 07:10 PM

If the car won't start in Park but does in Neutral, the starter safety switch is going bad. This switch (on the transmission) will only allow the starter to run in Park or Neutral so you don't start the car, with your foot on the gas, in gear -- it will immediately leap forward (or backward).

A bad shift linkage bushing will sometimes cause trouble, too, by not pushing the linkage all the way into the Park position.

Peter

#14 11-08-2002, 06:43 PM

Just picked my car up from Ultimate.

Raul said that the problem was that the fuel pumps (apparently there are two--never heard of that before), were not working properly and they were pulling two much amperage from the fuel pump relay. As a result the relay would heat up and not work properly. Since the relay would be warm after running, this is why it tended to not start after having been recently started. He said that I could replace the fuel pumpt relay as a temporary fix, but that eventually the same thing would happen.

He also replaced the fuel filter.

Car starts and runs great.

Replace fuel pumps, relay and filter. Total cost, including tax = $691. Is this fair?

David

96C220 · #15 11-08-2002, 09:24 PM

The odd thing is the only thing I can think of that would cause the fuel pumps to draw excessive current from the relay is some sort of blockage, forcing the pump to work the motor harder than ususal.

Maybe the fuel filter was clogged? or there was some other blockage in the line that caused a flow restriction, which was causing the pumps to work overtime?

I have never heard of a motor just randomly drawing too much current. Ususally the current of a motor is a function of the mechanical load placed upon it.

There is also some fused mechanisms here where if it was drawing huge amounts of current, it would actually blow the fuse. I havent seen the 420 SEL's fuel pump relay, but some mb relays have a fuse atop them.

The relay was definitely bad, the pump on the other hand - I'm not sure if it was bad or not.

Regardless for the work you had done it's a decent deal. And at least this way you wont have to look at the fuel delivery system for a while.

Take care,
George

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