280SE Spark At Coil But Not At Plugs

[FastPete]

Hey,

I'm trying to sort out my 280SE M110. It was running rough (stalling at idle). I checked the spark on each plug wire with a timing light and the spark on each cylinder was very erratic.

I replaced the Distributor cap, rotor arm, ignition coil, ballast resistors, and plug wires.

Now, I'm not getting any spark at the plugs. I hooked up a timing light between the coil and distributor and could see that it was sparking while cranking.

Just wondering if anyone could point me in the right direction and help me hunt down the problem.

Thanks in advance!

[rumb]

double check your rotor, make sure it is the correct one and it has continuity.  I have heard of people getting bad ones, especially if not original bosch. and make sure the spring loaded carbon pin is in place in the disti cap.

[FastPete]

Hey, The rotor has .5k ohm between the top and the tip. It's a Beru replacement. Does that sound right?

I might get a bosch rotor to be on the safe side.

I actually think I've lost spark between the coil and distributor now! I've run out of daylight so will need to wait until tomorrow to check again.

I re-checked all connections on all the parts I replaced and didn't spot anything out of the ordinary.

Is there an ignition troubleshooting guide that shows what voltages to expect throughout the ignition system?

EDIT: I found a troubleshooting guide on the online service manual. I'll run through that and report back.

[karmann_20v]

I had a similar issue in my 450SEL and was the rotor. If you have the old one, swap it in and see what happens.

Another potential issue is the green wire between the distr and the ignition control module, but check the rotor first.

[UTn_boy]

Be sure to check your ballast resistors, too.  If all else checks out, I'd suspect a corroded connection at the switching transistor unit, or even a bad switching transistor unit itself. 

[FastPete]

I went ahead and replaced the ballast resistors along with the coil. I'm hoping it's a connection problem as the wiring is a bit tatty.

I was thinking of the switching unit also. Hopefully it's not the cause!

Thanks!

[ptashek]

I went ahead and replaced the ballast resistors along with the coil. I'm hoping it's a connection problem as the wiring is a bit tatty.
I was thinking of the switching unit also. Hopefully it's not the cause!

The switching unit can be repaired cheaply.
If you need to do it, I'm local and can help out.

[w116john]

hi

i had a simallar problem and i ended up replacing most of the parts you mention,  but in the end it was the green wire from the distributor.

it had some chaffing and had worn through, it would fail intermittently it was the last thing i checked

all the best

john

[FastPete]

This is great. I'm going g to spend the weekend at it. I'll report back. Thanks for the suggestions!

[markb]

i had a similar problem and i ended up replacing most of the parts you mention,  but in the end it was the green wire from the distributor.

I often have very rough cold idling after heavy rains. I've replaced everything but the ECU, and the green wire. It APPEARS ok and it's insane cost makes me red in the face. John, may I ask what you paid for yours?

[ptashek]

i had a similar problem and i ended up replacing most of the parts you mention,  but in the end it was the green wire from the distributor.

I often have very rough cold idling after heavy rains. I've replaced everything but the ECU, and the green wire. It APPEARS ok and it's insane cost makes me red in the face. John, may I ask what you paid for yours?

Technically speaking, it's a piece of coaxial cable that is impedance matched to 600 Ohm +/- 150 Ohm.
Worst case, it should be possible to reproduce it at minimal cost provided the original connectors are in good order.

[w116john]

markb

when i was looking prices were a bit mad, it was cheaper to buy a second hand distributor with a good wire attached

i have seen some recently on ebay that were cheaper so keep an eye out.

i think a decent mechanic would be able to tell if the wire was working, i took my distributor out and had it tested and i was with him when he was testing it, and on initial inspection it worked but it was only after the cable was moved a bit did it start to fail.

give it a try

best of luck

[markb]

Thanks guys.. I figured it might have an impedance spec. And then there's the difficulty matching the color  . John, did your wiggle test require a scope, or just a DC continuity/short test? Now that I think about it, I suppose the reluctor or whatever lives inside the distributor could be sensitive to moisture? Once the car warms up, she purrs like a kitten. An old kitten.

[w116john]

markb

apologies for my lack of mechanical knowhow but the mechanic just spun the distributor and it obviously sent signal through the trigger wire which he measured with a voltmeter?

he assumed it was fine but on another attempt there was no signal, i bought another distributor and it turned out to be rubbish but the trigger wire was fine and i replaced that, i have had no problem since on the electrical side

no shortage of other jobs to do

[markb]

Thanks John, test procedure and no shortage noted!

Sorry Pete for going slightly off-topic (I think)!