300CE has no spark
 

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

Dokta:
I will check these out tomorrow 3/2/05 and let you know. I'm surprised the cam sensor is not relvant.
Thanks.

Hi, the Cam-signal L5/1 is only relevant to the ignition timing process of the module, not to its pulse output as in yes or no.
Dokta

Dokta:
Sounds reasonable. Thanks.

Dokta:
I have checked the items you listed ( I used a Sears Craftsman autoranging multimeter, model 82007):
-coupler #3/crank sensor: I got no ac voltage while cranking the engine over with the starter.
- coupler A: pin #1 (#1 at coil): continuity to coil and 12 volt dc at EZL.
pin #2 (#31 ground): continuity to ground.
pin #3 (#15 at coil): continuity to coil and 12v at EZL.
- coupler B: pin #6 (#31 ground): continuity to ground.
It looks like maybe I have a bad crank sensor?
Cary.

Have you checked all the fuses?

I had a problem where the car would turn over but not fire up, and all the fuses appeared ok froma visual look. I started removing each one and checking them, and found one that came apart when I removed it. I forget which one it was, but when I changed it, the car started right up.

Definately check them if you havent already, the fuses could look ok but actually be bad.

Alon

Hi,
no signal-no good. Change the sensor.
Dokta

Dokta:
Will do. I have one coming tomorrow. Ihave my fingers crossed. I'll let you know.
Cary.

Dokta:
Bad news! I replaced the crank possition sensor and still no spark! I tested the new sensor and did not get any voltage! I now don't know if I am testing it correctly or if my multimeters are junk (I have two - one older normal type and one newer electronic - I set the meter for ac voltage and put the red lead on the center socket of the sensor plug and the black lead on ground and crank the engine). I also checked to see that there was a tab on the flywheel - I found one.
So...I guess the testing is moot and I need a module.
Cary.

Hi,
instead of putting the black lead to ground you need to put it into the outer contact ring of the pick up cable end! But since you put in a new crank sensor already you are looking at the module now...gulp. Check with some guys on the forum to get a used one or try a used parts shop.
Good luck,
Dokta