Ignition testing...

[dotorg]

Does anyone have any good tips for diagnosing where a problem is in an ignition system?

After a week of futzing with this in the evenings, I finally got the stock ignition and the jacobs ingition installed in the car. I'm 90% certain that its all wired up correctly, with stock coin going through the secondary trigger, into the ignition computer, into the ultra coil, back to the distributor.

Poking around with a multimeter, I'm getting power and grounds as seems appropriate, but when I try to start the car, it never fires. I'm trying to figure out where in the chain of parts the problem is happening, but I'm not sure how one would test a coil, for example.

It appears the input side up to the jacobs ignition box is okay, when the car is cranking the "input" LED is lit up. The output LED, however, doesn't light up, and I haven't been able to figure out how I can tell if the problem is the ignition, the coil, or the wire going to the distributor.

Thoughts?

[dotorg]

*bump*

Anyone?

[Tim Walsh]

are you running points? if so are you getting a signal from them? sounds almost like you might not be getting any sort of "fire" signal from the points.

[dotorg]

I assume that the points are okay, because at least prior to reinstalling the jacobs stuff, the stock coil was working fine. I'm not 100% sure it still is because I don't have a connector on the end of the stock coil wire any more to try it with. Someone told me today I can just jam it into the end of teh distributor and it'll have enough juice to fire the plugs even without the metal tip/boot, so I may try that tonight to ensure its not something else.

Problem is the jacobs documentation sucks, and its not clear if the "input" LED turning on means its getting a valid input (ie, its seeing a reasonable series of timing signals from the secondary trigger(, or if it means something else. I'm assuming for now that "INPUT" being on means the stock coil is firing correctly and the jacobs is correctly reading it.

Without an oscilloscope, I can't think of any way to verify that the input to the jacobs is okay, so I'm trying to figure out how I can tell if its the jacobs ignition->jacobs coil link thats bad, if the coil itself is bad, or the link from the coil->distrubutor is bad. If I can cross those three off the list, then I can start looking at the rest of the stuff.

Someone suggested that I ought to be able to pull the signal wire from the distributor off and if I ground it and then unground it, I should get a spark out the other end of the coil. Presumably that means if I wired 12V into the ultra coil, and had a way to ground the other terminal, I ought to get a spark if its workign when I unground it. Maybe?

It'd be a lot easier if I had 8ft arms so I could turn the key while I was behind the car and could see.

[Early_S_Man]

A couple of ways to verify a 'proper' input and output to the coil ...

1. Connect a 12 Volt test lamp to the distributor lead after disconnecting from the distributor ... it should illuminate when the lead is ungrounded, and go out when the lead is grounded. This will verify that power from a 'pullup' resistor is getting to the points through the trigger lead.

2. Connect an analog multimeter [DC Voltage range; negative test lead to ground, positive to coil] to the 'hot' coil lead ... and ground the trigger lead several times, quickly ... you should see several needle 'kicks' indicating an output from the CDI-unit. Do the test both connected to coil, and disconnected [floating] from the coil.

3. Connect a new or 'good' used spark plug directly to the coil output tower ... without going thru distributor cap ... to test for HV output at coil while triggering the CDI-unit manually by grounding the trigger lead.

An oscilloscope with appropriate probes would be better for these particular measurements ... but sometimes you have to improvise!

[dotorg]

Did some more testing...

Points are fine. When I put the stock coil wire on the stock coil and just jammed the end in the distributor, the engine fired up just fine. I re-attached the jacobs secondary trigger, and did the rapid ground/unground of the trigger wire from the distributor, the INPUT LED flashed, so the input side seems okay.

Its looking like its something with the coil. Unfortunately I can't find any information about what the resistance readings should be on the coil so I can test it. No analog multimeter, either, and my digital one doesn't respond fast enough to pick up a voltage transient as fast as I'd be getting on the coil inputs from grounding/ungrounding the trigger line.

I'm hoping the coil is wired up correctly... with these aftermarket units, its just the two coil wires from the ignition computer, right? No power lines or anything? (Coil + to +, coil - to -, ground to ground and output to distributor?) I ask because the stock coil also has 12v going to it...

[Lorenfb]

Why are you not using a good stock Bosch CD unit? They're much more
reliable, produce an adequate spark, and keep your car original.

Also, they're simple to hookup and troubleshoot. Check out this
web site under Technical - Ignition Systems for possible insights
Also, the Diagnostics page may help with your present problem.

Loren
'88 3.2

[Lorenfb]

Forgot web site - Systemsc.com

[dotorg]

'68 cars didn't have a CDI system, just a coil.

[Lorenfb]

Then get a good Bosch CDI and don't mickey mouse it with non-Porsche
stuff.

Loren
'88 3.2