Intermittent stall after alternator replacement ?!

[FitzPR]

My alternator went out about a month ago, and as i was intending to do a commute from University (just finished my BSME at 34) to my internship, i changed it out in the parking lot of the AutoZone next to the school. Looks like the unit in there was the original one.

It had been intermittently not charging at startup, a quick rev had always woken it up before, but now it was gone, so quick swap.

At the end of the swap, i attempted to start it with the coil wire disconnected from the distributor. “Why isn’t it starting?” “Why do i hear big ol’ sparks?” “Oh duh” Plugged it in and drove off.

I get about a mile away, and the engine shuts off. No stumbling or sputtering, just like the key was removed. Cranks fine, won’t start. All connections and fuses look ok. The wire harness for the alt, is also the main power feed to the ECM, and it had felt a bit stiff and crispy, so my first thought was some kind of fault in there. It was a few days before finals, so i left it on the side of the road. Battery was a bit low, didn’t do a whole lot of poking before it wouldn’t crank, but the drive from the store to the failure was all low speed residential, bypassing massive traffic,so i think it just hadn’t charged much.

All indications are that the new alt works, though some kind of insidious no warning failure is theoretically possible, i think i can rule it out pretty safely.

Fast forward to two days ago, Saturday June 1st, i charge the battery, check the fuel pump is working (wiggle VAF, turn key with starter disconnected) Not really suspected, just being diligent, starting with the easiest checks. Says i to myself: “what if it just starts?”

It did.

Drove fine for little outing on Sunday.

One stall on the way to work this morning, but it started fine afterwards, and i was like a block away from work when it did anyway.

No issue coming home.

My current guess is igniter and/or coil, probably both are original, ~282k miles old, maybe they didn’t like having to crack off big long sparks while the coil was disconnected?

What y’all think?

 

[Kernal]

What model/year 80?

Check that all connections are tight of course including the ground to the inner left fender coming off the negative batt cable, ensure batt cables are tight on the posts, also check the fusible links on the positive battery post. Check that the high tension coil wire is connected securely at both ends.

After all that report back what you found then wait for in depth advice from an electronics expert.

Did you remove the battery when you replaced the alternator?

 

[FitzPR]

What model/year 80?

Check that all connections are tight of course including the ground to the inner left fender coming off the negative batt cable, ensure batt cables are tight on the posts, also check the fusible links on the positive battery post. Check that the high tension coil wire is connected securely at both ends.

After all that report back what you found then wait for in depth advice from an electronics expert.

Did you remove the battery when you replaced the alternator?

It’s a 94, and I did pull the negative while I was working.

But I think I found the problem! When the fault is occurring, there’s a bad connection, possibly at splice E5. There is only a tiny amount of voltage at the supply side of the EFI fuse. I used an add a fuse to feed it temporarily from a different source, and it works perfectly. I think I’ll probably run a separate cable back to the screw terminal for the Main fusible link to properly repair it.

So, my earliest theory that the harness had an issue resulting from my manipulation of it to get the alt out seems likely to be true

 

[LandLocked93]

Hope you found it.
If not and it craps out on you again, try wiggling all the wiring you disturbed in the process of replacing the alternator - at dusk or night time, w/o a light - looking for arcs.
If you find one or more, there ya go.
After replacing (actually just removing and reinstalling) my alt, I had an issue and found that the insulation on the alt terminal end had deteriorated and was arcing across to the case of the alt after reinstall.

 

[jonheld]

There is only a tiny amount of voltage at the supply side of the EFI fuse.

Are you certain that the main fusible link is not faulty.?
Fusible links have been known to become intermittent. The silicone jacket tends to hold the internal wires in place even after a fracture.
The fact that you installed a new alternator when the battery was in a low state of charge, points to a more than possible fusible link issue.

 

[FitzPR]

Are you certain that the main fusible link is not faulty.?
Fusible links have been known to become intermittent. The silicone jacket tends to hold the internal wires in place even after a fracture.
The fact that you installed a new alternator when the battery was in a low state of charge, points to a more than possible fusible link issue.

Yeah, it supplies full voltage, but it doesn’t make it through to the EFI fuse.

I’ve put in a wire from the link to the fuse (from circled C to oval 2), and now it runs reliably, except now the lights don’t work. The only thing that works through splice E5 right now is charging!

What doesn’t make sense based on the diagram, it seems like the taillights and such should work if the alt is working, they’re drawn as running from the alt in a separate wire. But they aren’t working, so it looks like I’m going to have to open up the harness to determine what’s really going on

 

[jonheld]

Yeah, it supplies full voltage, but it doesn’t make it through to the EFI fuse.

I’ve put in a wire from the link to the fuse (from circled C to oval 2), and now it runs reliably, except now the lights don’t work. The only thing that works through splice E5 right now is charging!

Well that certainly makes splice point E5 the prime suspect. Good luck.

 

[FitzPR]

boy do I feel dumb.

It’s the alternator terminal. It’s been like this the whole time, inside the boot. I didn’t need to open RB2, and route around the splice

Pic 2 shows what was actually still fully connected, about one half of the larger wire’s strands were not broken, shown here in “less green”

By the way, anybody know what size the larger wire is? The smaller one is roughly a 10 gauge.

Any tips on how to terminate these with new end(s) would be much appreciated.

 

[landtank]

The smaller wire is what would be 9 gauge if it existed. Run 8 gauge for both wires.

 

[FitzPR]

The smaller wire is what would be 9 gauge if it existed. Run 8 gauge for both wires.

That explains the slightly tighter fit than the 10 gauge wire in my Dorman yellow eyelet.

But i actually went ahead and did this, around the same time as when you posted:

The wires are about 2-3 inches shorter now. I squeezed it as much as i could using vice grips, then released em, tightened the screw, and repeated. Kept going past when i couldn’t pull the wires out, then soldered it together. (Using a plumbing torch on the tip of the eyelet, and pliers holding it at the base, that’s why there’s that orange line, that’s about the extreme edge of the flame). I wire brushed it, but didn’t get a pic of that

Still gotta trim the loom jacket and do some taping, but it seems to work