Informational post, did a search but did not find this scenario.

98 ML 320 intermittant cranks, no start or intermittant engine dies.

check fuel pressure, ok.

Check for ignition spark, none.

Crank sensor replacement (usual fix) no help.

Scope and pin testing, crank, cam sensors, coil resistance, wiring, all WIS ignition tests passed but yet no spark.

Applied 12 volts directly to coils (middle wire of coil connector) and engine
fired instantly. Jumped to coil fuse f26 same result.

Continued to back test wiring,cir15 terminal of ignition switch, burned contact, would flow enough voltage to pass all the BOOK TESTS but not enough amperage to supply the coils.

Replaced switch, ($15) available separate, pops out of the steering lock.

Replacing the $15 ignition switch restored the amperage capacity of the circuit. The engine started and has continued to run.


BTW, this was a former RAP vehicle,110000 miles and many ,many ignition cycles


This information has been provided by a clown who works in a stealership

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Paul

That very interesting. Is the part to which you make reference shown in the attached diagram? If so which part is it?

Attached Thumbnails

 

Ran across this problem before and it was a bad key. It would start and run for 1 second and shut down.

I AGREE WITH STAN TRY ANOTHER KEY, THEY HAVE A TRANSPONDER CHIP THAT FAILS, IT WILL NOT COMMUNICATE WITH THE COIL RING THAT IS AROUND THE IGNITION SWITCH CAUSING A ONE SECOND START AND STALL.

Ron in SC,
Yes, the ignition switch is in the picture but is not labeled.

S2 is the entire housing assy which is pinned to the steering column.

The ignition switch is the lower end of S2. The letter "N" of N24/4x1 is sitting on the ignition switch, the ignition switch pops out of S2 without removing S2 from the steering column.

BTW this was not a key or Das problem. Those were eliminated during testing.

__________________
Paul

Did it ever run again ?

__________________
Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

sdanville,
Sorry,

The last line should read, Replacing the $15 ignition switch restored the amperage capacity of the circuit. The engine started and has continued to run.

I will edit the post to reflect the success.

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Paul

I had this happen with my ML recently - and the computer did not see top dead center so it just turned and turned over - never started - except on rare occassion. Took about 4 days in the shop for them to find it - and now that they replaced the top dead center sensor it runs great...

__________________
W Hopper
GWS-MBCA President
Check out MBCA's Largest Event in 2010 - StarFest® 2010
www.starfest2010.org
http://twitter.com/starfest2010

Is this different than the crank sensor?

But that is how they described it to me. I am not a mechanic. But I do believe that that is what it is.

It has to know where the cranks shaft is to be able to fire the spark plugs.

__________________
W Hopper
GWS-MBCA President
Check out MBCA's Largest Event in 2010 - StarFest® 2010
www.starfest2010.org
http://twitter.com/starfest2010

What's a RAP vehicle?

__________________
Lenny

There are only three sports: bullfighting, motor racing and mountaineering; all the rest are merely games. --Ernest Hemingway

'10 GL550/'04 BMW 545/'99 BMW 323/'98 ML320/'87 VW GTI (race)

itb76,
RAP = Roadside Assistance Program vehicle=hard use,always doing something

All M-B dealers have one or more RAP vehicle to provide jump starts, flat tire replacement with the owners good spare, and 2 gallons of fuel for the rare times a customer runs dry. This is a free service to all M-B owners, subject to a mileage restriction, our dealership has an approximate 60 mile range, 24-7. 1-800-FOR-MERCedes

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Paul

To Replace it--- There is one electric clip and one bolt - then it pulls out. Under 3 minute job (now that I did it once)..
I bought mine online for about $55.00
I posted a picture of it on this site. At 1st I was sent the wrong one. Thats the frustrating part of do it yourself - waiting for parts via UPS.

__________________
Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

Thanks Paulwho. I've never had to use the RAP, though my wife did call 1-800-FOR-MERC once when the center bearing on the driveshaft gave out at 80 MPH. In central Illinois, outside of a good cell phone coverage area. Then the cell battery went dead. The only business in the area was a Lion's Den adult video store. She had two small kids with, but they were good about letting her use the phone. It was a real tale of woe, but I was able to borrow a neighbor's Suburban, hook up my race car trailer and drive 350 miles to get her, after it was towed off the Interstate. All's well that ends well, I guess!

Apologies for going so far off topic....

__________________
Lenny

There are only three sports: bullfighting, motor racing and mountaineering; all the rest are merely games. --Ernest Hemingway

'10 GL550/'04 BMW 545/'99 BMW 323/'98 ML320/'87 VW GTI (race)

Paul,

I have a 98 ML320 with a similar problem. The car stalled on my wife during a hot day. No Check engine lights appeared. I replace the Crank Sensor first. The car ran great but once the temperature gauge read around 85C and it is stop normally and allow to set for about 10 to 20 minutes it cranks( motor turns over but want fire). Open the hood allow the engine to cool down to about 80C and it fires right up. When it is cold it fires up everytime.

Next I replace the fuel pump and filter. The same problem occurs. It ran great down the road but when it is stopped and heat soaked it will crank but want start. Does not give a check engine light at any time.
It will start somimetime if you stop it and right way after restart.
Once it is hot it want start. It appears to be sinsitive to the temperature of around 85C. Any ideas.

Regards,
Don Mel