Ignition Troubleshooting......Meaning of

[jh225]

What is meant by "Terminal 4" in this scenario?

Starter turns, engine does not start or develops insufficient power:

1. Connect spark gap to ignition transformer terminal 4 and set it for 12 mm. Start engine

In deciphering the factory manual, I take that to mean. Make a 12mm gap to the coil terminal 4, but I have no idea what they are talking about by terminal 4

Later on in the troubleshooting it states:

5. Check ignition transformer.
Disconnect plug and high voltage wire at ignition transformer

Ignition transformer primary (term. A and B):
0.10 to 0.165 ohms

Ignition transformer secondary (term. 4 and A): 390 to 630 ohms

Talks about terminal 4 again but also mentions A&B which I would assume would be the 2 studs on the coil. That still leaves me wondering what terminal 4 is.

[Ericv]

Terminal 4 is the lead from the coil to the distributor. Primary "A" should be the input voltage from the CDI box and "B" should be the ground if I remember corrctley.

[scarceller]

Looking at the schematics:
Term 4 is the center hi-energy wire on the coil, it's where the spark wire that connects the coil to the center of the distributor goes.
Term A & B are the 2 posts on the coil these goto the CDI pins 1 & 2 but neither is ground these are simply the isolated outputs to the coil in the CDI setup the coil sees several 100 volts on the primary (not simply 12 V) so be careful working on these posts or the wiring to them with engine running. The CDI simply charges a large internal capacitor to a few 100 Volts then dumps this energy to the coils primary at the correct time as indicated by the distributor's magnetic pickup.

In the end if you measure the resistance across the 2 posts (A&B) you should read .1 to .16 ohms (very near 0 ohms)

Then measure resistance from the hi-energy center (Term 4) to either of the posts should read 390-630ohms

I'm simply not 100% certain but my bet is it's not Ground but rather one side of the large capacitor - most likely the CDI box isolates the energy circuit to the coil from the main cars ground circuit so not to induce excessive noise into the cars ground circuit. I could be wrong here maybe someone who knows the inner working of the Bosch CDI can help?

[scarceller]

This may help, I created this simplified schematic from the master schematics:


In the upper right notice the delay relay, this is a special relay located in the engine bay on the left side tin just above the 3 fuses. This delay relay comes on the minute the Fuel Pumps come on and this is what powers pin 8 of the CDI, so the pumps must be running for the CDI to come on. But when you shut the car down the pumps shutdown first but the CDI stays powered for 3-5 seconds by the delay in the relay. The idea here is to allow the motor to burn any extra fuel before the engine stops.

[304065]

Google DIN 72552