94' Cobra Dies with AC is on

No the factory cobra pulley (the original alternator) appears to be smaller than the stock GT version. So i am actually running the alternator faster with the stock GT replacement alternator. I bought a DC clamp amp meter today. When it arrives I will test the amperage coming from the alternator charge wire.

I feel as if something is going goofy with the charging system from a wiring standpoint. However, I am not savvy enough to properly diagnose all the wiring. I tried it before as a temporary test, but may install a more permanent heavy gauge ground directly to the alternator mounting bolt.

RioRed95Cobra said:

Do you know anyone with another computer? This whole thing sounds so odd.

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I have went way past crazy with this car. It is my Unicorn.

Yes, I went down that road several steps ago. I have a spare stock GT computer in the trunk i swapped out in previous iterations. I could give it another try. It only takes about 15 minutes to swap.

The last time I tried it the car would still noticeably miss around 2000 rpm with the AC on (same results both computers). However, it has made a weird evolution since then. Now it runs fine with the ac on, but completely dies off when the voltage drops below 13V. Typically after heavy electrical loads at idle maybe 10-15 minutes depending on how many accessories I turn on.

It's the labor of love I suppose.....

Unfortunately, I haven't had much luck with professional shops in the past. They usually poke around replace something trivial and it magically runs more so out of coincidence than corrective action. I pay $400 and it starts getting weird again. Happened with my, dare I say, Dodge Daytona....AKA Turbo-Turd

I think I am finally headed down the right road......I hope this proves to be reality and not another trick.

Today I received my clamp ac/dc fluke current meter. I clamped the alternator charge wire and the main battery cable to the fuse box in the engine compartment. I also left my multi meter on the battery to sense the voltage. Here are the results with the replacement alternator.

Idle with no accessories on:
charge wire 15-20 amps / main fuse panel wire -8amps ( - means charging battery, ie flowing from fuse box to battery)

Idle with ac/headlights on:
charge wire 50-65 amps / main fuse panel wire -5amps ( - means charging battery, ie flowing from fuse box to battery)

Idle with ac/headlights on/rear defrost:
charge wire 50-65 amps / main fuse panel wire + 0-2mps discharging (the alternator isn't keeping up)
ultimate dies in short order, the voltage ticks down until about 12.5 or so at the battery maybe 12.2 dead

---Swap back to original alternator---

Idle with no accessories on:
charge wire 15-20 amps / main fuse panel wire -8amps ( - means charging battery, ie flowing from fuse box to battery)

Idle with ac/headlights on:
charge wire 70 amps / main fuse panel wire -8amps ( - means charging battery, ie flowing from fuse box to battery)

Idle with ac/headlights on/rear defrost/radio on turned up:
charge wire 80-82 amps / main fuse panel wire + 0-1amps discharging (the alternator isn't keeping up)
ultimate dies in short order, the voltage ticks down until about 12.5 or so at the battery maybe 12.2 dead

What I noticed today. The pulley size difference was actually opposite of what i thought and a slightly larger difference than I originally thought. The replacement stock GT alternator came with a larger pulley. I originally assumed the larger pulley would make it spin faster....Duh it was opposite. The pulley on the replacement alternator is approximately Ø2.5" and the stock cobra pulley is Ø2.125". The 3/8" in diameter difference accounts for about a 15% difference in rpm. So what I am experiencing is a new alternator that is spinning about 15% slower than the original.

Just doing the basically math 15% of 65 amp ~ 10 amps. Adding 10 amps to the new alternators max amp output 65+10=75 amps. This still doesn't look like I have enough charge amperage on idle? Judging from the test with the original alternator I need at least 85-88 amps on idle running all accessories. I feel like I have been duped with the replacement alternator. It was one of the first things I replaced and I think the replacement is a pile of junk.

Next step....Try to swap the original pulley to the new alternator. If it still doesn't put out the amperage of the original I want to melt down in a forge. I also ordered a new replacement alternator. In the world of ty parts, why does it always have to be the one you least expect???

Longest story ever....Told in short hand format.

It was always the alternator. D'OH....The original went bad and the replacement was a marginally functional piece of crap. It would not maintain voltage and caused all the other systems to function improperly. It figures that the original culprit was one of the first items I replaced. I did not realize this until purchased a Fluke clamp on DC amp meter. This lead the way to the solution. Replaced the alternator with another replacement version and all is well again!!!

And the trauma continues....She got towed today after driving through a little rain.........I have a moisture related short. The weird part is it reacts identical to the way it did before the alternator swap. Thinking about a new regulator plug end and maybe a new AC clutch. Any ideas on what would short bad enough to cause charging issues when wet? I am going to spot check in the driveway by target spraying different components with water.