How do i check a coil with a timing light??

[irl]

71T wont start and Im not getting spark at plug ends. I was told I could check the coil with a tining light, anyone know how? I have one but have never usd one.

[Kemo]

i guess if you had an inductive timing light...just put the sensor on the coil wire instead of #1. Ive never done it, but logic would say that the light would just be on all the time like a flashlight. ill have to try it now

[irl]

Im going to try it now.

[acapella8]

subd

[irl]

With the battery in the front I cant get the gun power because the cables are not long enough......

[rattlsnak]

It would be just as easy to unplug the coil wire and check it for spark. But does your car have points or electronic ignition?

[irl]

It has points and I managed to get the gun powered up and no light. CD box is whining, I have a new coil, should I try that next. This all started when I put new plug wires in. It ran for a great test drive and died suddenly in the garage when I got back in the garage. Turns over with no start.

I have new points, cap and coil but did not want to complicate things more.

[BK911]

Originally Posted by Kemo

i guess if you had an inductive timing light...just put the sensor on the coil wire instead of #1. Ive never done it, but logic would say that the light would just be on all the time like a flashlight. ill have to try it now

That will work but won't always tell you if the coil is bad. Sometimes the coil will give off a weak pulse, not enough to spark the plug but enough to light the timing light. Chased my tail for hours because of that! Best way to check a coil is to check the resistance across the terminals. The haynes book has the procedure and the values.

[HarryD]

Originally Posted by irl

With the battery in the front I cant get the gun power because the cables are not long enough......

Ed,

Our Pals at Porsche solved that problem for us. On the Left side of the engine room is an electrical panel with three fuses. They are hot when the engine is turned on. Just hook on.

[HarryD]

Originally Posted by irl

It has points and I managed to get the gun powered up and no light. CD box is whining, I have a new coil, should I try that next. This all started when I put new plug wires in. It ran for a great test drive and died suddenly in the garage when I got back in the garage. Turns over with no start.

I have new points, cap and coil but did not want to complicate things more.

To get a spark to the spark plug in the engine. Several things need to happen. First, you need power to the CDI. Next you need to have a way to trigger the CDI (the points do this by opening and closing). Then the CDI will then send a pulse to the coil which will increase the voltage and send it through the high tension lead to the rotor and to the selected spark plug. You need to verify that each step in this chain is working.

1) Verify that the CDI is getting power. Do you hear it wining (if it is a Bosch unit)? If so, you are good to go.

2) Verify that the CDI is producing power to make a spark. You can do this with a "telegraph" test. Take the high tension lead off of the center of the distributor and put a spark plug on it. Ground the threaded part. With your plug attached to the center lead, open the distributor, remove the rotor, place your key in the run position, and manually open and close the points. Each time you cycle, you should see a spark from the plug. If you do not, you may have a bad CDI.

3) Verify that the coil gets a signal when you crank. Replace the rotor and distributor cap. Leave the plug on the center high tension lead. Crank the engine. Do you see a spark? If so, you are getting spark to the distributor. If not, your point gap may be off or there is some other problem with the connections.

4) Verify that the spark goes to the spark plug wires. Reattach the center lead to the distributor. Attach you spark plug to one of the leads going to the cylinder spark plugs and ground. Crank engine. If you see a spark you may have a timing problem. If no spark, you have a problem with your rotor or distributor cap or your wires are improperly seated.

Do a search here as there are many threads on this topic. Look especially for the ones by early_s_man. Warren (RIP) left a great deal of knowledge on troubleshooting this problem.

[Wayne 962]

I would use a dwell meter to check the signal from the points, although putting the timing lamp on the coil signal wire is a good test of the points / trigger / coil system too. If you're getting a good, strong signal, the problem is somewhere in spark distribution...

-Wayne

[irl]

Thanks I have been reading old articles all night, here is the one you discussed.

History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

I am having problems understanding the telegraph test. How do I attach a plug to the high tension lead and how do I ground the threaded part????

[BlueSideUp]

You can ground the threaded part to the fan housing.

As Wayne said I would check your points. I had the exact same problem after replacing the points on my '70T. I installed the tabbed washer backwards and it was grounding the points out.

I just checked for continuity from the rotor to the distributor and found that no matter if the points were open or closed I still had continuity.

[HarryD]

Originally Posted by irl

It has points and I managed to get the gun powered up and no light. CD box is whining, I have a new coil, should I try that next. This all started when I put new plug wires in. It ran for a great test drive and died suddenly in the garage when I got back in the garage. Turns over with no start.

I have new points, cap and coil but did not want to complicate things more.

Did you check to see that the wires are seated properly? What may have happend is the lead fromthe coil to the distributor worked it's way loose. Press them into plase. You may need to "burp" the trapped air out of the boots to get them fully seated on the distributor and coil.

[BlueSideUp]

Oh and it doesn't feel good to get zapped by the plug so wear gloves and don't touch the metal part of the plug. Take it from someone who learns by trial and error.

What distributor do you have in the car? Ts generally had the Marelli distributor but quite a few had the Bosch aluminum body unit as well. My car had an older cast iron body Bosch.

[irl]

Sorry to be slow here, Im actually quite intelligent with this stuff. -- Is the high tension lead the center wire from the coil to the distributor.

And if so I am fitting a spare plug up in it and touching the threads to the fan housing while I manually open and close the points.

[DW SD]

Originally Posted by irl

Sorry to be slow here, Im actually quite intelligent with this stuff. -- Is the high tension lead the center wire from the coil to the distributor.

And if so I am fitting a spare plug up in it and touching the threads to the fan housing while I manually open and close the points.

Ed,
High voltage (tension as you called) is indeed the fat (+/- 1/4" diameter) center wire from coil to distributor. You can also use a test wire to ground the plug. I grab the spark plug electrode with a wire with alligator clips on two ends. The second clip I attach to a solid ground. From there, I don't run the risk of being in the path to ground, which won't kill, but will make you jump.

Doug

[irl]

Thanks for all the support, Ill put it to work in the morning. Last question. I just think its odd that this happened after new wires went in, it seems ironic that I would lose my CD or coil minutes after the wires went in. The wires are tight and burped and I have not replaced, rotor, cap or points but I do have them here. My question is, could new wires cause anyhting to burn out suddenly as a result like points. The new wires are Magnecor.

If no ,I feel like it would have to be a ground or a connection came lose by the sudden stall.

[HarryD]

Magnecor wires can be tricky to seat properly on the plugs. Giv them a good push onto the plugs,you should feel a "click" if they seat properly.

[irl]

Well after going thr telegraph test, and coil test listed above and both showing spark, I put it all back together and it started. Who knows. I think I need to really go through and replace and check all grounds and wires with broken coatings. Its all a little messy in there and i feel it has something to do with what I just went through. But it runs nice, just put the new cap and rotor on, still started. Now I have to figure out the new point install. Thanks for all your help.