My 1990 300CE (I have owned it for 9 months) all of a sudden would not start. My instinct (I have worked on cars for 45+years) was no gas or no spark. I could hear the pump come on and run for 1-2 secs. with ignition on so that seemed o.k. I then removed the distributor/engine cover and checked for spark from one of the distributor cap connections - none. I then pulled the plugs and they smelled of gas. I checked the coil as per the M-B manual and it seemed o.k. but it was old so I replaced it along with the distributor cap and rotor and plugs. Still no spark. I then received the "time-honored" advice from a M-B mechanic - change the overvoltage protection relay: while waiting for the new relay to arrive I checked the old one and found it to be o.k.(this car has the 9-pin setup), but I changed it anyway. Still no spark. I suspect that the ignition module is not functioning. I would like to be able to test the module and the various inputs to the module. A replacement module, used or new, will be bery expensive.

Hi there,
the ignition module in deed is very expensive and you want to be sure about it. Start here: Switch on ignition. Take your test-light and test coil terminal 15 (it's marked as such) for 12V- bright test lamp. Good? OK- Let someone crank the car now while you test the other terminal -1 (also marked) for a pulsating test lamp. If you got your pulse on Term. 1, you can be almost certain you've got a good module. If there's no pulse, you need to check the main inputs into the module before knocking it for bad.
Tell me how it went and if necessary I'll give you the detailled procedure on the input test of the module.
All the best,
Dokta

Dokta:
I tested the module switched output to the coil (#1 from XA connector) with a voltmeter and got a steady reading - no pulse or switching. I need to test the inputs to the module - there seems to be 6: cam sensor, crank sensor, coolant temp. sensor, throttle valve switch, CIS data and MAS. Of those it seems to me that the cam and crank sensors are probably the ones that the module can't operate without. I do not find any help in the various manuals I have/have access to, including the M-B CD-ROM. What's your advice?

Hi,
to be on the safe side, give me the VIN# and i'll check the wiring diagram for the respective inputs.
All the best,
Dokta

Dokta:
The vin# is WDBEA51D3LB165548.
Thanks.

Hi,
Here's the set up: Coupler 1: A16g1 and g2 (knock sensors), Coupler 2: Trimming plug. These two connectors are not relevant for your issue. Coupler 3: L5 crankshaft pos. sensor (measure about 1V AC from the pick up at crank speed!) Coupler 4 or A: pin1- signal 1 to coil, pin2-signal 31(ground), pin3- signal 15 to coil, pin 4-TN eng. speed signal to N16 MAS, pin5- shielding, pin 8- toX11/4 diagn.coupler, pin7 -to N3 inj.ctrl..
On this coupler you want to verify signal 1,15 and 31, the rest is not relevant for your "no spark" issue.
Last, coupler 5or B, you got pin1-L5/1 cam sensor, pin3- S65 AT overload protection switch, pin4-B11/2 coolant temp., pin5 shielding, pin6- 31 ground, and 7 and 8 being idle and full-load switch from throttle. Here really relevant to you are only pin 6, ground.
Let me know what you found.
All the best,
Dokta

Cary,

90 300CE, W124 Coupe, 104.980 motor

I seem to have a similar problem and wanted your advise if possibe. I read thru the thread and have a few questions.

Pulled in the drive way and it hasn't started since. Turns over, no problem. I assumed it was the coil, an Ohm test showed open, both coils. Replaced it. Still nada, wont start. Replaced the plugs, cap, rotor, still nada.

I have 12v, goin into the coil, both sides, same as you did, and only 12v comming out of the coil. No pulse, just 12 constant. Shouldnt this be a much higher voltage?
From the camshaft pos sensor, I have .5v ac when cranking...no good?
Continuity from the Coil to the module, and ground, same as the pins you tested.
Is the Crank sensor easy to replace? I cant seem to find the end by the flywheel.

Any recomendations on what to do next, aside from purchase a new ECU and hope that solves it?

Thanks in advance for any input you can provide.

__________________
Dean

Just sold em all !! Curently driving a, 06.5 VW GTI

90' 300CE
Euro Lights w/wipers, Clear corners, 17" Monoblocks, K&N Airfilter, Sportline Suspension, Custom SS single muffler exhaust
80' 300D
96' Harley Davidson, XLH 1200