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Hello, I recently had my car run into a no-start issue after changing some dash lights.  Whilst changing the dash lights, I created a power-ground short at the speedo.  I'm worried this somehow or another created a short back to the CDI via the TD pin from the Tach.  Not sure what is possible other than I know the car was working fine before the dash light mishap and is not after.

I pulled the old CDI and found that D1 on the internal circuit was a short circuit, not behaving as a diode should.  Additionally checked the spark and it was very weak.  The CDI had a HV whine, so I don't think it's dead.  Just not operating how it should based on the blown diode.  The diode also was the incorrect size (must be from a rebuilt) and since it bridges from ground to power, I figure my dash incident could have caused this. 

Long story short, I bought a CDI+ to replace my old CDI.  I'm a bit nervous to plug it in to the car without knowing that the rest of the electronics are fine.  Is there some pin test I can do to verify that the plug is seeing the expected operating conditions before plugging the new toy in?

As far as I can tell, I fixed the short in the dash and don't seem to have any issues else where.  Everything lights up, fuel pump operates, and can't identify any other issues from my limited experience.  Appreciate your help and looking forward to the new product!

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@gtgrad CDI 6 pin connections are as follows looking at the PLUG** on the harness with it's two keyway 'ears' at the top

A  top left:  COIL 'A'

15 top middle: 12V

7 top right: Distributor Signal +

31/1 bottom left: COIL '1'  (-)

TD bottom middle: Tacho Drive

31d bottom right: Distributor Signal -

**Note:  The sticker on the side of the CDI case shows the CDI SOCKET connections on the unit as you look into the connector.

 

Basic checks

CDI box disconnected.  At CDI plug on loom with ignition OFF:

Check resistance between pins 7 and 31d.  Should be around 600 Ohms.  This is the resistance of the pickup winding in the distributor (must be plugged in to distributor of course!).    If you can plug the meter in whilst wiggling the green wire, it should stay locked at this reading.  If it goes open or short circuit, then the green wire is bad.

Check that TD is not shorted to GND.

 

CDI box disconnected.  At CDI plug on loom with ignition ON:

Check 12V between pins 15 and 31/1.

 

 

 

 

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@Jonny Retrofit

Checked both items mentioned and got ~580 Ohms between pins 7 and 31d.  Wiggled the green wire and didn't see any changes.  TD is not shorted to ground.  With the ignition on got battery voltage ~12V across pins 15 and A.  

Installed the CDI+ unit and gave it a crank.  Still not firing.

The tacho does a sweep from 0 to 7k RPM to 0 on key on.  When I turn the key it goes to 1-2 kRPM sorta of erratically.  Turn it off, turn it back on and basically same behavior.  

I'm assuming (hoping) that the CDI+ should be fine.  But I'm not sure what else to chase down here.  

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Black Bosch Coil:  0.221.121.001

Resistance between terminal A and 1 with CDI+ disconnected:  0.6 Ohms

Resistance between terminal A and center:  690 Ohms

Resistance between terminal 1 and center:  690 Ohms

I can't test the cranking visual behavior without my assistant being home.  I did check when I turn the key on, the green light turns on for about a second.  As soon as she gets home, I'll do a spark test and check for flashing on the CDI+ box.  I guess the good news if both of those come back as acting as normal, then I have a functioning ignition system.  One step closer to a functioning car I guess.. 🙂

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@Jonny Retrofit

Checked status during cranking and got a flashing green LED. 

Attached a plug to the center lead from the distributor and got a pretty healthy spark on crank.  It was for sure brighter than the spark I got with my older CDI, so I think the ignition system to the coil is working.

I'm going to check the individual cylinders with a timing light tomorrow to verify each of them is getting a firing signal from the distributor. 

From there I'm thinking it could be a fueling issue.

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@Jonny Retrofit

Worked on the fuel system sensors today and found a loose connection in the CSV circuit.  It happened to start getting a bit cooler here around the same time I started all this work, so I think this may have been a coincidence.  Fixed it and it fired back up!

Back to a running vehicle with a much improved ignition system.  I also have your fuse kit on the way, should have a functionally modern classic car soon enough.  Appreciate all of your suggestions. 

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