electrical gremlin, car dies while driving?

[TastyReuben]

Odd problem has developed in my 83SC past few weeks. While driving it will occasionally switch off, no sputtering, just flat line like the light switch flicked off. Occasionally I will see the tach and other electronics flick to 0 and then jump right back up if I'm doing 40-50+, and sometimes I've just got to roll off to the side of the road.

Then the car is in a no-click no start condition, but emg flashers still work? Takes a jump from my portable box immediately and the alternator test on there shows good.

First time was right as I shifted from 3rd to 4th for the first time that day, earlier I had been working on the sunroof motor and radio replacement so I assumed I just didn't have enough juice in the battery. But the problem has become more frequent, and now seems to be 50/50 when I come to a stop. Idling and revving in the garage will not re-produce the issue far as I can tell.

Recent work on the car would be the sunroof / radio swap that killed the battery twice and a heat backdate project where I deleted the engine bay blower.

I'm running the battery over to AutoZone for a check up, but I let the car sit for the past 15 days and it just fired up first try. Strange. hoping for some other clues from the Pelican brain trust on this one, thanks!

[911obgyn]

Grounds, remove and clean them even if they look tight. Clean and tighten fuses. Easy stuff first.

[Bill Douglas]

Originally Posted by 911obgyn

Grounds, remove and clean them even if they look tight. Clean and tighten fuses. Easy stuff first.

Yep, there are half a dozen locations around the car. The workshop manual will show you where they are. And while you're at it also check and clean the engine to body ground.

[TastyReuben]

thanks will try that. Anyone have a list or drawing of the ground locations handy?

[dannobee]

Or the plug for the ignition switch that goes to the frunk area. Make sure that it's not loose.

[PeteKz]

The fact that the tach goes to zero when the ignition stops firing indicates that the CDI box lost power, or has an internal problem. In addition the the usual grounds others have mentioned, specifically look at the brown wire from the CDI connector, and to the ground point on the inside left fender.

[TastyReuben]

Originally Posted by PeteKz

The fact that the tach goes to zero when the ignition stops firing indicates that the CDI box lost power, or has an internal problem. In addition the the usual grounds others have mentioned, specifically look at the brown wire from the CDI connector, and to the ground point on the inside left fender.

I think you are onto something since that's where I was working when I did the heat backdate, I removed old wiring for the blower and an engine bay light that's long gone, and had to move the ignition coil to get the new cover plate in and squeeze it through some wiring there. Hopefully I didn't damage the CDI unit itself ?

[TastyReuben]

Originally Posted by PeteKz

The fact that the tach goes to zero when the ignition stops firing indicates that the CDI box lost power, or has an internal problem. In addition the the usual grounds others have mentioned, specifically look at the brown wire from the CDI connector, and to the ground point on the inside left fender.

All the wiring and grounds look good to me, with the car running I’ve been shaking and pulling various wires a bit to try and recreate the problem but no luck. Is there a way to open the CDI box for visual inspection?

[PeteKz]

Yes. Four screws on the back remove the back cover. If you don't see anything obvious, send it to Bob Ashlock for testing and rebuilding. I would plan on spending the $350 or so he charges to rebuild it, even if it tests good, because his rebuilds are better than original, and those units are 40+ years old now. Check his web site.

[TastyReuben]

Which fuse is the CDI on? Chasing a few theories here.
Also I’ve read that when the CDI goes bad it can be a heat problem? which might explain why I can’t recreate the problem in the garage easily

[gwmac]

I had the same or very similar symptom, turned out to be the coil.

[TastyReuben]

Originally Posted by gwmac

I had the same or very similar symptom, turned out to be the coil.

How did you diagnose that? Just swap coils and pray? Mine appears to be original but who knows.

[Schulisco]

Originally Posted by TastyReuben

How did you diagnose that? Just swap coils and pray? Mine appears to be original but who knows.

Most of coil related issues are due to insulation issues due to engine heat and vibrations.
Carry a spare coil and a can of ice spray with you, make a test ride to provoke the symptom. If it happens cool down the coil with the spray, but don't freeze it! Try to start the engine. If it starts - voilà! Replace the coil and be happy.
If not - bad luck. No, no, just kidding
Then cool down the CDI box in the same way to rule this out too.
You can use a MSD8222 coil as a good replacement. They're vibrating resistant due to being tar filled (instead of oil which spills when mounted overhead) and could be mounted overhead as the original coils too.

Thomas

[gwmac]

finally got bad enough to replicate in the garage,had a timing light and voltmeter on it and located it

[mysocal911]

Originally Posted by PeteKz

Yes. Four screws on the back remove the back cover. If you don't see anything obvious, send it to Bob Ashlock for testing and rebuilding. I would plan on spending the $350 or so he charges to rebuild it, even if it tests good, because his rebuilds are better than original, and those units are 40+ years old now. Check his web site.

Really? Please explain how you arrived at this conclusion? Have you opened one and analyzed the circuit board and components being used?
What are the inadequacies of the original Bosch CDI? Have you done comparative electrical tests?

[mysocal911]

Originally Posted by PeteKz

The fact that the tach goes to zero when the ignition stops firing indicates that the CDI box lost power, or has an internal problem. In addition the the usual grounds others have mentioned, specifically look at the brown wire from the CDI connector, and to the ground point on the inside left fender.

Or lost the trigger signal from the distributor.

[PeteKz]

That too. As for better than original, take it up with Bob. See his website.

[mysocal911]

Originally Posted by PeteKz

That too. As for better than original, take it up with Bob. See his website.

If you believe everything that's posted on the internet, please get some help.
As they say, "The blind leading the blind".

[TastyReuben]

Originally Posted by mysocal911

Or lost the trigger signal from the distributor.

Would this be the green wire from distributor? Checked on it and seems ok. I was going to open the distributor and clean it up, but what I don’t understand is why the car would be in a no click no start condition after shutdown. What on these cars can prevent a start? Other than a dead battery.

[Schulisco]

Originally Posted by TastyReuben

Would this be the green wire from distributor? Checked on it and seems ok. I was going to open the distributor and clean it up, but what I don’t understand is why the car would be in a no click no start condition after shutdown. What on these cars can prevent a start? Other than a dead battery.

Yes.
Be aware - that inductive pickup signal is pretty low on voltage and power. The green cable is a shielded cable with a thin center core. If there are any minor breaks or contact issues they can cause running issues for sure. But - in case of a breakdown while driving and no immediate restart afterwards, try to wiggle a bit on that cable while a helper person try to start the engine ... if it then starts you got the culprit. Another option is to use a spare green cable if possible, but they're pretty expensive. If your cable insulation is hardened that much due to the engine heat over the decades it's basically a good idea to replace it anyhow. My SC used to have the longer green cable with 700mm length:
Longer cable part no: 928 602 907 00
https://www.pelicanparts.com/search/?q=928+602+907+00
The shorter version: 930 602 907 01
https://www.pelicanparts.com/More_Info/93060290701.htm?pn=930-602-907-01-OEM

But I don'texpect that because your issue seems to be heat related as this happens only when engine is hot. Also heat issues are not so common with the green cable. Nevertheless it's definitely worth a check.

Dead batteries can also be an issue, but not so much on CIS cars. Later injection systems have a voltage surveillance and if voltage is too low while cranking they prevent engine start as they expect a serious problem. A CIS - no matter if its a lambda controlled or a pure mechanic version - won't do that. If they gets electrical power they will start somehow.

Basically on CIS cars almost every part can cause a no start situation, because any component works for his own without caring others. So any contact, any cable, any seal, any hose, everything.

Here's a good troubleshooting guide referenced by the cis911primer.com website:
https://cis911primer.com/Troubleshooting%20Guide/Notebook%20Spiral.html
It focuses on CIS related issues, but also others. I also believe your issue is caused by electrical issues. But this might be also a good approach to narrow the issue down.

Also https://cis911primer.com/pages/test_troubleshoot.html#TS_chart

I still vote for the coil. Check that first as I described earlier. If the coil hasn't been ruled out, chasing for any other issues makes no sense.

Thomas