No Spark - CDI Testing

[jjrowe]

Does you snap on meter have a current setting? If you look at the schematic http://forums.pelicanparts.com/showt...=cdi+schematic the current through the signal wire through the points to ground should be (Vbatt - 0.7) / 1000 ~ 12 milli amps.

Ooops messed up on that, missed a resistor. should be 12 / 33 or 0.36 an amp.

Yes, I can measure current so I will check that by grounding that wire through the meter. Your post reminded me that there is no signal from the points per se, its just supplies a ground when the points close. My first test when I get home will be whether the wire to the points is grounded when disconnected, indicating a short to ground.

Jesse
76 911S

[rick-l]

I think I would proceed like this

1. points open 12 volts on the wire
2. points closed 360 mA through the wire

this is at the distributor
Someone will correct me if I'm wrong

[jjrowe]

Fixed it! There was a short between the signal wire from the distributor and ground. I first checked the resistance and there was none



The wire shield had cracked and the metal shielding was touching the internal wire. I had to peel back the shielding to see it. Once I fixed that the car started on the first crank. I forgot how much fun that car was to drive!



Thanks for all your help

Jesse

[Simonrex55]

I had the same issue as I wasn’t getting the car to start. I jumepered power from the rear window heat fuse to the red wire on the box and i was able to start. Now i know the problem is upstream, or is that downstream, on the other side of the rear firewall

[Fred Winterburn]

Good work tracking that down. Short of a lightning strike right on the car, I really don't see that shielding is necessary to prevent spurious triggering of the CDI. I wonder what test scenario or real life circumstance made them do it, or whether it was arbitrary since it's a signal wire? Most CDIs don't need shielding on the points signal wire and I don't think the Bosch 3pin does either. Fred

Originally Posted by jjrowe

Fixed it! There was a short between the signal wire from the distributor and ground. I first checked the resistance and there was none



The wire shield had cracked and the metal shielding was touching the internal wire. I had to peel back the shielding to see it. Once I fixed that the car started on the first crank. I forgot how much fun that car was to drive!



Thanks for all your help

Jesse

[b00mslang]

No spark on my 82' Coupe. So, I swapped the coil on my running 79' Targa and still no spark, however, the White wire to the coil was connected to terminal "1" instead of terminal "A" (as per Bentley's and how it was wired up on my Targa). The coil off of the Coupe started the Targa so it's not the coil and my CDI on the Coupe is whining away. I haven't check the points yet.

[JSV798]

You have points on an '82 car? My earlier car (1978SC) doesn't have points; the distributor generates a pulse that passes down the green wire to the CDI. This wire can short. Result no spark. Suggest you check the green wire by putting a meter across the two wires after you have detached it at one end. If you have continuity then there is a short.

[b00mslang]

What about the wires being effectively crossed between the 2 coils? That is, on the 79' the White wire was connected to the "A" terminal on the 79' but connected to the "1" terminal on the 82'? They both ran that way but I didn't think they were interchangeable. The White to terminal "A" is as per the Bentley manual but the 82' has it wired up backwards.

I haven't pulled the distributor cap and just assumed points.j

When you say: "put the meter across the 2 wires", which 2? The green and...?

[JSV798]

The green wire is known to fail. It's actually a shielded cable; if you disconnect it (on my car I can do this somewhere near the oil feed for the chain tensioner) you will find two pins; these two pins should show infinite resistance or no continuity. My meter has a buzzer for checking continuity. If you can't find this connector then disconnect at the CDI and check for continuity between pin 7 and 31d.