Fried ECM

[wot440]

All this talk about fried ECM's is making me hungry....

Good one! You guy's are a riot.

Good to see it's not a Buick. Had me going for a while. Hey just for giggles, what's your charging voltage?

14.1

 

[AJ/FormS]

Old post I know, but since a resolution was never posted; I'll thro my 2cents in.

One other thing I can add is... after it dies, it will crank with no spark, and spark at the release of the key and fire for a second then die.

1) it will crank with no spark
2) and spark at the release of the key
3) and fire for a second then die.
These are three problems;

As to #1,
see note1 below
as to #2
This is called ; "the one spark test", and confirms the ECU is able to command a spark. It tells you; the ECU and coil are alive,and the case-ground is working; therefore the entire circuit is working, in "run mode". It does not say anything about the pick-up.
as to #3
If you get more than one spark while cranking, but the sparks quit while cranking after a few;this indicates the entire system is working in "crank-mode"; but for some reason, one or more items in the system went into hibernation.
As for the coil and it's ballast, and the powersupply system, they all work with points, so must be good.
That leaves just four things;
the pick-up,
the case ground,
the crank circuit,
or a faulty ECU.
As for the pick-up, see Note #1 below
As for the case ground, and Ecu: they passed the one-spark test, so I wouldn't condemn them yet.
note #1
That more or less just leaves the pick up inside the D.
To test it, I usually pull the D out and spin it's driveshaft with the key in run position. But if you don't want to pull the D,for whatever reason, then; you will need to get the pick-up out of the D and stroke the magnetic "pole-piece" with a piece of iron; I use a small screwdriver; key in "run". Every time your iron leaves the magnet it should send one spark. It does not matter in which direction you stroke it. Some pick-ups need a more rapid stroking than others. You are trying to simulate a minimum 300 rpm cranking signal . You cannot stroke too fast.
No multiple sparks means pick-up is dead.
If you do get multiple sparks, then there is a mechanical problem with the reluctor; it might just be too wide a gap,(spec is .008 to .011 using a non-magnetic feeler gauge) or there is not enough iron in it's construction, or it's magnetized. If you pull it off the shaft, take note of which slot is on the roll-pin index; they are marked with arrows as to in which direction it should be rotating in your D. My testing has shown that most pick-ups will spark reliable enough to idle, at no more than .030, and will still spark at .000,lol, ie rubbing.
If you get multiple sparks, and the reluctor is doing it's job; then is it possible the spark is getting lost inside the D? I have seen the Pick-up resistance running and working at between 150 to 350 ohms.

I know some,a lot, or most of this diagnostic, has been posted in preceding posts, and the guys have posted good stuff. This post is a recap, and puts it all on one page, so that if you want to try it again after your points need work, it should be an easy diagnostic. I like Del's test apparatus, and since your junk is now on the bench, using his diagnostic, that should point you in the right direction

My gut feeling;
since the engine quits while running,
and you then get no sparks while cranking;
I think you will find the problem in the pick-up. With a slim chance it could be a power supply interruption.
That's the best I got

When all else fails; check your alternator for an A/C component; you may have, but I doubt it, a blown diode.

 

[wot440]

Been a while. Quick update. With Pertronics in. I deleted the fusable link, from the 12v starter selonoid to the bulkhead connector, and also bypassed the bulkhead connector for that circuit with a soldered direct connection. First time the engine run without a misfire in forever. I think this could have been the root of my electrical problems. So... I also made the same direct connection for the alternator and brown ignition wire.

 

[AJ/FormS]

I deleted the fusable link, from the 12v starter selonoid to the bulkhead connector, and also bypassed the bulkhead connector for that circuit with a soldered direct connection. First time the engine run without a misfire in forever. I think this could have been the root of my electrical problems.

That is what I did as well,(except the fusable link) with same results. Whoah
Except;
with the fusible link gone, you now have no protection in that hi-powered circuit. And so, if a short develops,your car could catch fire . What I did was run the ignition off a relay, triggered by the key, to remove the load from my OEM 1968 ignition switch. And then I subbed in a small gauge wire for the fusible link. Eventually, I found a correct F-Link and installed it. No more worries.

 

[wot440]

That is what I did as well,(except the fusable link) with same results. Whoah
Except;
with the fusible link gone, you now have no protection in that hi-powered circuit. And so, if a short develops,your car could catch fire . What I did was run the ignition off a relay, triggered by the key, to remove the load from my OEM 1968 ignition switch. And then I subbed in a small gauge wire for the fusible link. Eventually, I found a correct F-Link and installed it. No more worries.

Thanks. I certainly do not want a fire. I'll try to source a new fusable link for protection. Will a fifty year old fusable link deteriorate over time?

 

[AJ/FormS]

Will a fifty year old fusable link deteriorate over time?

Yes and no;
The wire will survive quite nicely, but the insulation does get hard, and sometimes brittle. But the big thing is that after so many years it may have been heat-cycled so often that the wire has become fatigued, or some strands may have come loose, or the ends are fragile.
That F-link is like a slow-blow fuse. It's job is to melt before the rest of the wiring gets hot enough to catch fire, but it takes more time to melt than a regular fuse does to blow. And over 50 years, it may or may not ,have been cycled dozens of times, there is no way of telling, except by stripping the wire and examining the strands.Unless it has obviously failed.
Two signs of obvious failure are; melted insulation, and/or separation inside the jacket when you try to pull it apart. A third sign is wire discoloration.
F-links are color-coded;the color indicates it's wire size and power-handling ability. You replace yours with a same colored one. And a same length one. They are crimped in; not soldered, then insulated and sealed.
If I can, I double crimp, the second one at 90* to the first. The quality of the crimp is very important. If you create a high-resistance connection right from the get-go, you could get stranded on the side of the road.
Do not bury it in a sheath, it needs to be air-cooled.
I know; rules, rules, and more stinking rules........

 

[wot440]

Thanks for that explanation. When I looked at my fusable link, it seemed weak. As I could bend it into a 90* angle or more and it would just bounce back as if there were no wire inside at all. When I stripped it, there were around ten very small dis colored wires, that totaled the size of a no.18 ga. wire or smaller. Just did not seem this was sufficient for the integrity of my voltage needs. IDK. I did take the car out today. Run smooth with no misfire noticed. Brakes still need some work so No WOT testing in this 4K pound boat with zero road feel.

 

[67Dart273]

When you say "deleted" did you provide an alternative fuse/ breaker? VERY dangerous. Those old girls are not well protected in the fist place, and removing the fuse link adds a LOT of room for a Great Big Failure

Examine the basic diagram from the MAD article, which shows what is NOT fused

from here Catalog

So you bypass that and now none of the ammeter wire is protected, nor the bulkhead connector, not the ammeter, nor the wire going back out to the alternator. The headlight circuit has a breaker in the switch, but the wire from the switch to the splice and back out to the battery is not protected. The wiring to AND FROM the ignition switch is not protected, nor the main feed to the fuse panel "hot" buss.

 

[wot440]

When you say "deleted" did you provide an alternative fuse/ breaker? VERY dangerous. Those old girls are not well protected in the fist place, and removing the fuse link adds a LOT of room for a Great Big Failure

Examine the basic diagram from the MAD article, which shows what is NOT fused

from here Catalog

View attachment 1715529931

So you bypass that and now none of the ammeter wire is protected, nor the bulkhead connector, not the ammeter, nor the wire going back out to the alternator. The headlight circuit has a breaker in the switch, but the wire from the switch to the splice and back out to the battery is not protected. The wiring to AND FROM the ignition switch is not protected, nor the main feed to the fuse panel "hot" buss.

Appreciate your help. I read through the upgrade and will be using this as a template before driving the car. As I stated, I certainly do not want a fire. Is there a specific length to use for the fusable link? Thanks again.