CDI Help

[LFogelson]

I have an '82sc that cut out yesterday.. hesitated with loss of power under load, backfired and stalled. I could restart it if I let it cool with ignition off. It would only run for 30sec, then 15 sec and then not at all.

My pop-off is ok, if I push the plunger in the air box I hear the fuel pump and smell gas. I pulled the center ignition wire and I get a spark to ground. I went through Bentley and tested the voltages on the CDI harness and they were as expected 12V on terminal 15 and a pulse between 7 and 31d.

However, I tested the resistance on my rotor and found it was 5 kohms, the rpm limiter type. This has been on the car over a year without problems. In my archive searches it seems this is for row cars, but I have a us car with 02 sensor and frequency valve.

Also when I took a spark plug wire, connected an old plug and grounded the threads, I got no spark. Is this a weak CDI, bad ignition rotor.

Does anyone have a CDI unit in the Baltimore area? or have any ideas or suggestions?

thanks

[Early_S_Man]

Sounds like a rotor or cap problem to me. The fact that you got a spark from the coil lead tells me the problem is 'downstream' from there.

The center carbon button may be broken or missing, or, there may be a crack in the rotor allowing an arc to ground, intermittently.

Check the coil for leaking and oozing goo, and check the resistance ... 0.4 - 0.6 Ohms on the primary, 650 - 790 Ohms on the secondary. If there isn't a spark gap 'load' for the coil, it can arc internally ... flashover' is the term Bosch uses in official documents.

One final note ... the CDI output Voltage is slightly lower when the engine is fully hot and ambient temps are above 85°F. Any problem in the spark path can cause a miss or cutting out.

Since this is an intermittent problem, my suggestion is to replace the cap and rotor with USA-spec parts ASAP!

[LFogelson]

thanks early_s I will check the coil resistance. However, the problem is not intermittant. The car has run well as a daily driver until yesterday. Since the stall it restarted with a lot of hesitancy smoke and smell 4 more times and now it will not start at all. I visually checked the rotor and cleaned all of the contacts.

[LFogelson]

The resistance on the primary coil is .5 ohms. How do you check the secondary? Also I am still trying to track down a new rotor and a CDI unit that I can swap in. Thanks

[Superman]

I think a cap and rotor for your car costs a total of less than $20. I find, and I've reported here on a number of occasions, that caps and rotors are a wear part, and if yours are older than 10-15K miles, then you need to change them.

Also, I just recently, this weekend, had an ignition problem. Thanks, Warren, for your help. The problem mysteriously went away, but not until after the car twice refused to start at all during dozens of attempts. I think unplugging and re-plugging the CDI plug simply improved a corroded connection. The green wire sends a very wimpy signal to the CDI box.

So I'm suggesting it could easily be something as simple as that. Poor connection wimpy signal. Or, it could be on the high-voltage end, like Warren suggests. Ignition systems are incredibly persnickity. They've got wimpy signals, and then they've got that high-voltage end. The cap, rotor and ignition wires. High voltage electricity behaves pretty interestingly. That signal is so anxious to get to ground, that it's choose the most interesting paths. If you cap is old, it'll run right down the dust particles on the inside of the cap and ground to the distributor body.

I (and I think Warren) am suggesting that you deal with the simple stuff before you go sourcing a replacement CDI box.

[LFogelson]

My cap, rotor and manecor wires have about 5k miles on them, that is why I suspect the CDI. I was hoping I could find someone else with an SC in the area to do a temporary swap for diagnostic purposes. My only hesitation is I do not want to ruin someone elses CDI unit if there is another problem in my car; but this doesn't seem likely and maybe I can first try putting my CDI on someone elses car. thanks

[Early_S_Man]

You check the coil secondary by inserting the multimeter probe into the coil output tower terminal #4, and touching terminal #1, the grounded common terminal.

To be sure, get confirmation of CDI problems ... take the car to a shop with an old Sun Analyzer ignition scope, and have them look at the signal at the coil #4 lead while the engine is running with the oil temp at 180°F or higher.

[Gunter]

Green wire from distributor to CDI module o.k.?
I would try a regular rotor with new cap and find a dark garage to check for sparks wandering.
Swapping a CDI module makes sense; I keep a spare one just in case.

[LFogelson]

I decided to install a new MSD 6420. I could get my old CDI to work cold until a high rev and then it would stall and the buzz with the ignition was not constant. No time or resources to try and R&R the old one so I bought the MSD ignition and Hi vibration coil.

The install of the MSD was straight forward (thanks to other MSD installation posts for 6pin connector) until I broke the positive battery terminal connection to the starter... another post. But today with a new starter the car is running very smooth. Further, I haven't even regapped my spark plugs yet as recommended by MSD. Thanks everyone for the help and input.