Author Topic: W108 "Beverly" intermittent spark (I think)  (Read 2166 times)

K-Jet

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W108 "Beverly" intermittent spark (I think)
« on: November 28, 2022, 15:43:59 »
Good afternoon,

So I have cleared all the documentation hurdles (did you know that California listed VINs using model names- 280SE 123456 instead of 108 018 12 123456? I didn't either- until now. Neither did my local DMV. They needed a lot of convincing) and now have 30 23 days to get the car in for a safety inspection, which I don't think should be a problem as it has all new fuel lines, brake lines, rebuilt calipers with new pads, and more already done. But it does need to run all the way to the inspection station (~25 miles) and back. Today is the first time I've had it on the autobahn, though for only 10 miles or so, and at moderate speed (indicated 60 MPH).

The motor died when exiting the autobahn, wouldn't restart, and I had to be flat-bedded home.  It still wouldn't restart after it was offloaded in my driveway. I think it's spark because when trying to start it, the timing light didn't flash. So I
  • Checked / adjusted / tightened the points
  • Checked voltage at the coil- 3.8 V
  • Checked resistance at the coil- 0.6 ohms
  • Checked resistance of the ballast resistors- both measured about 6 ohms without disconnecting them. There's continuity there, so that's enough, right?
  • Checked resistance of the coil wire- 1064 ohms
Reassembled. Still no start.

Pulled a spark plug, connected it to plug wire 1, and there was spark. Not only that, the engine started and ran just fine on 5 cylinders. A few more starts with the timing light. When the timing light stopped flashing, the engine stumbled and RPMs dropped. Sometimes this could be solved with the application of more throttle, sometimes it just died.

Then it ran beautifully for 30 minutes all around town before I parked it for the day.

The problem seems to be intermittent. The other ignition components check out. So I suspect the transistor ignition box (CDI box in Porsche-speak) Ideas? I've had no luck finding a backup / known good ignition box.
« Last Edit: November 28, 2022, 18:04:21 by K-Jet »
Dru
_____
1971 280SE "Beverly"
1990 250D 5-speed "Opa"
1995 E220T Sportline "Sport Kombi"
1980 911SC Targa "Petrol"

K-Jet

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Re: W108 "Beverly" intermittent spark (I think)
« Reply #1 on: December 03, 2022, 20:43:25 »
So I drove the car about 30 miles today to drop it off at the inspection station. The day was colder and the speed lower (no autobahn). I had a bit of stumbling about halfway there, but it cleared up.

This is not inconsistent with intermittent transistor box failure, as lower temperatures and lower RPMs would be less heat in the box, less heat expansion, and therefore lower chance of disturbing an unstable connection.

Has anyone opened up one of these? Anyone repaired one, or know someone who does?

Many thanks.
Dru
_____
1971 280SE "Beverly"
1990 250D 5-speed "Opa"
1995 E220T Sportline "Sport Kombi"
1980 911SC Targa "Petrol"

lpeterssen

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Re: W108 "Beverly" intermittent spark (I think)
« Reply #2 on: December 05, 2022, 11:44:15 »
Dear K-jet

There are other transistorized ignition boxes that work the same way.  They get the signal from ignition points and then the box sends signal to the coil.  You can get another system like that new and just change the connector terminal types.

The other workaround is to bring the car back to pure ignition points and condenser wiring scheme using the appropriate ballast resistor values.

It seems that you are specialized in k-jetronic system, it would be nice to be in contact when I put my hands on my w119-6.9

Be in touch

Best regards
L.Peterssen


Best


lpeterssen

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Re: W108 "Beverly" intermittent spark (I think)
« Reply #3 on: December 05, 2022, 11:54:29 »
Here some other news ignition control modules that would do the magic.

But…. If you plan to spend 200 to 400$ in a new ignition control module would be better to change the whole distributor for a new one sold by the people of 123ignition Germany which cost around 350$ and is a full new electronic distributor which does not require any external parts apart from the coil.  Looks original, it’s from hi quality and you will have no more problems related to spark.


lpeterssen

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Re: W108 "Beverly" intermittent spark (I think)
« Reply #4 on: December 05, 2022, 13:24:41 »
Here two electrical wiring schemes.  One for the traditional ignition point, where the coil field is interrupted at the negative side to generate the main spark thru terminal 4.  See figures/elements 30, 38, 39 (second attachment)

On the transistorized ignition the field on the coil is interrupted on the positive side. Generating the same effect. (First attachment)

Enjoy.

« Last Edit: December 06, 2022, 00:23:24 by lpeterssen »

K-Jet

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Re: W108 "Beverly" intermittent spark (I think)
« Reply #5 on: December 06, 2022, 16:45:11 »
The ignition123 solution looks very clean and reliable. I think that will be better than counting on 50 year old electronics. Thanks for the reminder!
Dru
_____
1971 280SE "Beverly"
1990 250D 5-speed "Opa"
1995 E220T Sportline "Sport Kombi"
1980 911SC Targa "Petrol"