Greetings,

The car (84 380SE) is now sitting in the garage, cranks but won't start. I have observed that there is spark on an earthed spark plug attached to the distributor end of coil wire, but no sparks on the spark plug wires (tried on wires for cylinders 1 & 2.

Now the fact that this is happening, does that mean the problem *IS* either cap, rotor or HT leads?
AND that the ignition module (on fender inner) and other electrics (coil, distrubutor, resistors, green wire etc) *are* working properly?

My understanding is that *if* some on the electronics are down, eg distributor inners, green wire to ignition module or the moduel itself, then there wouldn't be sparks at all anywhere.

Other info: OVP and ignition coil are new, the cap and rotor are 5 months old, all HT leads have aroud 1.1k ohms, and I have tried starting with my old cap and rotor (which was old but working).

Thanks guys and any comments would be appreciated.

This is the part of the program where "substitute known good unit" would be real handy (if you had an ignition module). The ignition modules are known for failure on that year model. The weird part is a "partial" failure. Usually they either work or they don't. I wouldn't suspect the rotor or cap unless there is a ton of carbon tracking. Coil failures are rare and the over-Voltage protection relay isn't even in that circuit. If you knew what Voltage the spark output was it would help. If I had to guess(man I hate to guess) I'd go for the module. If it helps, you can use a module from an early (1984-85) 190E 2.3. Really.
Regards,
Randy D.

I've had in a couple of instances both on 380 models the harness at the ign. control module, not the wire to the distributer but the 4 wire harness was defective. It tested good with a mutimeter but for some reason replace it corrected the problem. No comebacks yet.

Just wondering, what equipment do I need to measure the voltage at the spark plugs? What capacity would be good? 40kV, 50kV?

To measure KV in the secondary side of the ignition you need an oscilloscope. There are several "variable gap" tools available that can give a good estimate,however...it is suggested that they not be used on electronic systems because of the "potential" for damaging components. The system should be capable of 38,000 to 40,000 Volts but anything around 20K is more than enough.
Regards,
Randy D.

Hi Randy,

Thank you for your info. With regards to your earlier post about ignition module, does my car's symptoms fit partial failure of the module? I got the car to start few times today but it stalls soon after and then is *very* hard to start again. I am unable to get a loaner module and it's a rather expensive part to do trial & error...

I have tested these:
- Jack 5 of diagnosis socket is battery voltage against ground.
- Voltage difference between jack 4 and 5 is 0 volt
- Green control line resistance between terminal 3 and 7
(inner and outer of the plug) are about 650 ohms
- dwell angle I cannot measure.
- the plug on the distributor end of the green wire is cracked, but all connections looks fine.

I don't suppose this proves that the module is fine, and as Stan pointed out the wire harness could be defective. On top of electrical problems it could be fuel as well...

I still hope I can fix the problem myself, but looks like I will have to get the car towed to a MB specialist for repairs, but at least I wish to know what could be wrong so I don't get ripped off...

Here's my other post regarding starting problem, it's got extra info and historyhttp://www.peachparts.com/shopforum/showthread.php?threadid=20883)

Thanks again for everyone's help.

Regards,

Bill

Greetings,

Thank you everyone for your input and help.

As a final hope/try, I got a second hand ignition module today, came home, plugged it in, and the car started straight away.
Whew...glad I didn't get it towed yesterday...

However, the car idle fine in P or N, but rpm would drop very low (but didn't stall) when put in gear or A/C switched on. Does this have anything to do with the ignition module?

Thanks again.

Best Regards,

Bill