78SC won't start - ignition

DaddyGlenn · DaddyGlenn's Garage

First some history... For several weeks, at random times, the engine would just shut down. I couldn't tie it to anything. Sometimes it was while driving down the road, other times i was sitting at a light. It usually fired right back up on the first shot or even restarted itself before the engine completely spun down. It was not a fuel issue as the restart often resulted in a back fire (igniting the unburnt fuel). I figured I had a loose wire or a rotted 30 old wire. I put this trouble on my list of things to dig into.

Then the other day, after an uneventful drive to my son's Cub Scout meeting, she didn't want to start when it was time to leave. A friend helped with some quick diagnostics in the parking lot and we discovered that there was no spark.

The car is now home in the garage and I have begun my troubleshooting. Following the Bentley manual, I have eliminated the cap, rotor, distributor pulse unit and all the wires connecting them. Bentley suggests that my trouble is in the CDI or the coil.

Is there any way to test a CDI and coil, short of replacing them? Do these symptoms sound familiar?

The CDI is only 5 or 6 years old but I suspect the coil is much older.

I await your collective wisdom.

jtfreels · 01-22-2009, 08:46 AM

Glenn, sounds just like the problem I had... when you mention "distributor pulse unit" what do you mean?

In the end my problem was the magnetic pickup coil inside the distributor, (connects to the green wire) I would get 655 ohms (or what ever) on the green wire. But after it ran for 5/10 minutes the engine would die, the green wire was "open" and it would not start till it cooled off.

Jay

DaddyGlenn · DaddyGlenn's Garage

Quote:

Originally Posted by jtfreels

Glenn, sounds just like the problem I had... when you mention "distributor pulse unit" what do you mean?...{snip}

The Bentley manual actually calls it the "distributor pulse generator" which is the magnetic pick up coil in the distributor. So according to Bentley, mine is good.

jtfreels · 01-22-2009, 10:07 AM

Ok then, didn't have a Bentley when I was working my problem

Here is a link on testing the CDI CDI whining, new coil, but no spark from coil

I gathered up a bunch of links related to ignition on my blog, in the 2008 section.

Good luck.

Jay

T77911S · 01-22-2009, 10:20 AM

mine was doing the same. i thought it was related to the engine getting warm, then i think it just kept getting worse. i replaced the permatune with MSD and it ran perfect for a year, then it did it again. i sent the MSD back and they tested it and it was fine. i replaced the coil and all is well.

DaddyGlenn · DaddyGlenn's Garage

thanks Jay! You just gave me my next step. I'll tear into the CD box in a day or two.

T77, I guess if I end up replacing one then I will just do the other, too.

I just need to confirm that one or both of the suspect parts is indeed the cause.

kodioneill · kodioneill's Garage

i would replace the hall effect unit in the distributor. the wire coil inside is fine as hair. when they get old they sometimes open causing the failure particularly when hot. i wouldn't mess with the cd box most of the time they just fail and aren't intermittent.

good luck

pozee · 01-22-2009, 01:37 PM

Glenn,

Your situation got me thinking about this thread:

Momentary total ignition failures...why?

DaddyGlenn · DaddyGlenn's Garage

Quote:

Originally Posted by kodioneill

i would replace the hall effect unit in the distributor. the wire coil inside is fine as hair. when they get old they sometimes open causing the failure particularly when hot. i wouldn't mess with the cd box most of the time they just fail and aren't intermittent.

good luck

I don't think that is the problem. I can see voltage spikes generated when cranking but the car still won't start. By the process of elimination, either the CDI is not sending the current to the coil or the coil is not sending current to the distributor. It looks like I will be replacing both the CDI and the coil but I would like to confirm a failure before investing a couple unemployment checks in the parts.

P.S. anyone need an efficiency/process improvement guy?

DaddyGlenn · DaddyGlenn's Garage

Of course now I just went out and turned the key. I don't know why I did it. I just felt like it. Wouldn't you know the damn thing started right up.

pozee · 01-22-2009, 04:52 PM

Did you read that other thread I posted a link to? Seems you're having similar issues.

Jiggle the ignition switch while the car is running and see if that affects anything.

In most instances, the CDI and coil will either work or not. Sounds like a loose ground or ignition switch problem. Then again, the CDI and coil may intermittently cut out when hot if they are defective - but not likely. Have you tested the coil for correct resistance?

Good luck, this sounds frustrating.

DaddyGlenn · DaddyGlenn's Garage

I did read the other thread. and it sounds very similar. I am now reconsidering the pulse generator/hall effect coil in the distributor. After all my earlier trouble shooting, I never tried to start it until this evening.

I'll check the resistance on the coil and keep the multimeter in the car for a while. very strange....

jtfreels · 01-22-2009, 06:29 PM

Next time it dies on you (sorry I'm not an optimist) check the resistance on the "green wire" I'll bet its open.

Jay

DaddyGlenn · DaddyGlenn's Garage

Quote:

Originally Posted by jtfreels

Next time it dies on you (sorry I'm not an optimist) check the resistance on the "green wire" I'll bet its open.

Jay

No worries. I'm sure it will die, too. I doubt it is the green wire,though. I replaced that 2 years ago. I am really leaning toward what others have suggested, the pick up coil in the distributor. In fact, I ordered one last night.

pozee · 01-23-2009, 03:44 AM

I meant jiggle the KEY around in the ign. switch with the engine running to see if that affects anything.

kodioneill · kodioneill's Garage

Quote:

Originally Posted by DaddyGlenn

I don't think that is the problem. I can see voltage spikes generated when cranking but the car still won't start. By the process of elimination, either the CDI is not sending the current to the coil or the coil is not sending current to the distributor. It looks like I will be replacing both the CDI and the coil but I would like to confirm a failure before investing a couple unemployment checks in the parts.

P.S. anyone need an efficiency/process improvement guy?

glenn even though there are spikes in your reading they often are not strong enough to trigger the cdi.

CliffBrown · 01-23-2009, 09:18 AM

It's often the "green wire".

Lot's of threads about this problem.

DaddyGlenn · DaddyGlenn's Garage

The pick up coil arrived this afternoon. Our host was all out so I was forced to order it elsewhere. If you need one now, PM me and I'll share my source.

I pulled the distributor and swapped out the old for the new and reinstalled it. The kids just went to bed so I'll wait for tomorrow to fire it up and reset the timing.

holtjv · 01-26-2009, 05:48 PM

I have an extra cdi if you need it--pm me. Jack

ischmitz · ischmitz's Garage

Our hosts sells a rebuilding sevice for CDI units. A simple test is to listen for the whistle of the box with the ignition turned to ON. If you do not hear that chances are the box needs repair.

To trigger a 6-pin bix you need to hook up a 1.5 battery to the trigger input. The negative pole of the battery goes to the signal wire and the postive pole goes to GND of the car. That way you can test if the trigger circuit of the CDI box is working.

If you get failures that worsen with time and only after some driving you might have a box on tis way out. They latch up when they get hot and start to work again after sitting for a couple of minuites when you cycle the ignition. This is a typical failure mode.

Ingo