Car falls flat on it's face at 4,200 rpm

[99FiveOh]

Still sounds like the alternator to me. A diode could be bad and still allow the alt to charge a little. Then shortly it goes out. I'd have it checked someplace else.

Also, when you ran a wire from the back lug of the alternator to the block on the fuse box, did you get any charging? if you didn't, then you ruled out wiring.

 

[99FiveOh]

Another thing, to explain why you have continuity with the Red/Green wire.

On your regulator you will see the letters: A S I
The A is your battery monitering circuit, this tells how much voltage is needed for battery maintanence. This is an uninterupted circuit strait to the battery/block.

The S is for the "Stator" circuit, you'll see this wire come out of the reg. plug and go right back into the stator plug. This tells your alternator to start charging.

The I is the Red/Green wire, it is grounded UNTIL the alternator starts charging. This is because it is what powers your idiot light inside. If the alt doesn't work, you'll have power to one side of the idiot light and a ground on the other side, which in turn makes the light come on. When the alt starts charging, there will be a positive charge on both sides of the light, and as a result, it will go out.

Another thing about the ( I ) circuit is that the bulb in your dash breaks the power signal down to 8 volts. This is the initial signal that powers up the regulator in the first place.

 

[HISSIN50]

Thanks for all your helps guys. One more quick question. I've been probing some things this morning and found continuity between the green/red wire on the plug for the alt regulator and ground. I shouldn't have this right? Thanks.
- Justin

EDIT: I somehow missed the post above mine while glancing through this the first time.

Some basic regulator info: The Green/red wire is an essential item to get the alternator to start producing current. The ignition switch sends power down the wire, through the battery light and to the regulator. The regulator supplies a ground for this wire when the alternator is NOT producing voltage. This is why when you turn the key-on but dont start the car, or your alternator is crapping out and really not making voltage, the battery light comes on. If everything is ok, the regulator removes the ground and the light goes out.

There is a resistor to mimic the draw of the battery light, in case the battery light fails.

 

[badstang123]

I still haven't figured this thing out. There is still zero ouput from the alternator no matter what the rpms. Here is what I have done:

- Checked all fuses
- Bench tested alternator
- Checked all power and ground cables
- Put new alternator plug
- Disconnected rear battery (To make sure it wasn't the problem)
- Chased all wires to look for bare spots or missing insulation

Today I took the voltages of the wires leading to the alternator plug. Here's what they were:
A - 11.9 volts
S - 15v when car first started - then fluctuated between 12.0 and 13.0
I - 11.6v

What should these wires be at? If the A and I are a bit low it is probably because when the car is off the battery is the usual charged 12.7 volts, but once started, since the alternator isn't charging the voltage at the battery is 11.9 while the car is running.

What would you do next guys? Thanks.
- Justin

 

[99FiveOh]

Did you have the alternator retested? Somewhere else? Did you run a line strait from the lug on the back of the alt to the pos. battery terminal?

 

[grrrrrrr]

Disconnect your positive battery lead and hook an ammeter in series with it. Better yet buy an ammeter that you can clamp around a cable. Start your car up and see how many amps you're pulling. If your alternator generates 200 max amps then all throughout your cars operating range you should see less than that. I'm better something in your car is pulling way more amps than it should. And if your car is falling flat on it's face at 4k rpm then you're losing spark or fuel. Prolly spark... Check your plugs, make sure one isn't burnt through in a less than obvious place and shorting to the block... Check the insulation on your plugs by running the car at night and looking for arcs.. You can't see these during the day. First thing to determine though is whether your alternator is putting out amps at 4k or whether it's pooping out.

 

[99FiveOh]

Well, if the plug was shorting on the block, it would only do so when that plug was supposed to fire anyway, on top of that, the coil will only draw so much power from the charging system to accomplish this anyway, so that wouldn't cause his draw.

I still suspect the alt is bad. In my last post I explained how to completely rule it out. If it checks out, then we can go on to the next step. The charging system on a Mustang is very simple, there can't be too much more than a bad alt or bad fusible link. Also, he said this happened when he got rid of the U/D pullies, that wouldn't point to the plugs or any of the ignition system.

 

[badstang123]

If you guys look a couple posts back after I had it pulled and bench tested it did the same thing when I first drove it and now I don't have any output from the alternator at all (It runs at 11.9 volts when the car is on with no charging what so ever. This is at any rpm. I did run a power wire straight from the alt to the battery. That didn't do anything. I'm going to have the alt retested tomorrow at a different shop, so we'll see what they say.

 

[99FiveOh]

If you are getting the voltages to all the wires going into the regulator, like you said earlier, and you had no charge when you ran a wire strait to the battery, then the alt is toast. I don't care what the first shop told you. They built it and are probably too proud or cheap to admit it's bad.

Hopefully the next test will show the truth.

 

[badstang123]

I have a slightly off topic question but related. Can you spin an alternator too fast? I put the stock pulleys back on and the crank, and waterpump and then a slightly smaller alt pulley. Do you think that could fry the alternator?

 

[HISSIN50]

I have a slightly off topic question but related. Can you spin an alternator too fast? I put the stock pulleys back on and the crank, and waterpump and then a slightly smaller alt pulley. Do you think that could fry the alternator?

All accessories have a critical speed; for 3G's, it's about 15K RPM. If you know the crank and that alt pulley diameter, you can figure out what kind of critical speed your alt might see at redline.

Good luck.

 

[99FiveOh]

I seriously doubt you over-spun the alternator. All that would do is wear out your bearings. However, if the bearings are somewhat bad, the alt would show it's charging on a test, but when the alt gets spun to a certain RPM, the bearings start to seize causing your car to fall on it's face, as you describe.

 

[badstang123]

I got the alt retested at Pep Boys today and it put out a whopping 8.62 volts. I guess that's my problem. It's just odd to me that the other shop checked it and said it was fine, I put it back in and it had the same voltage drop at high rpm (But worked normal at a lower range of rpms), and then after one rev up it died completely.

I did some math with the pulley sizes:
Crank Pulley = 6.5"
Alt Pulley = 2"

Crank Circumference = 20.41"
Alt Circumference = 6.28

1 Crank rotation = 3.25 alt rotations
4000 rpm = 13,000 alt rpm
4500 rpm = 14,625 alt rpm
5500 rpm = 17,875 alt rpm

According to what you said Hissin, it shouldn't be a problem till over 4500 but my problems start (Before it blew up that is) at 4,000 and above. You guys think I'm overrevving the thing?

 

[99FiveOh]

You might be overrevving it. I have an underdrive pully on my alt, but stock pullies everywhere else and it seems to work well that way. Buy yourself a new alt or get the shop to rebuild that 200 amp one and have a stock sized pully put back on.

 

[HISSIN50]

I cant comment firsthand about the possibility of a failure because I tend to play it safe with pulleys, but IMHO it would not surprise me at all that the alt couldnt handle the stress and heat from excessive revs. That's just a pile of conguessture (conjecture+guess) by me though.

A lifetime warranty unit might be a nice idea (for when this happens again) - and have this current one rebuilt for a spare (unless you have an extra car, etc and this doesnt have to run 24/7). Most of the online alternator vendors dont require your old core............

Good luck.

 

[badstang123]

I took alternator back to the people who built it and they said the stator went bad. They blamed it on an extremely large draw that caused it to go out. There going to replace it with a 240 amp stator for me though. We'll see how things work out once I get it back in.

 

[99FiveOh]

They are full of crap! A large draw my a$$! Do you realize how much you have to be running to reach the capacity of a 200 amp alternator? Remember, our alternators are what the Fox guys are upgrading to because even at 130 amps it's damn near bullet proof!

If it was short circuited, then it's possible that might have caused the failure, but it's doubtful. You would have remembered the short because it's alot like shorting the battery out, big sparks etc.!! I'm glad you found the problem and it's being fixed! Let us know how it runs afterwards!

 

[gcomfx.com]

A draw that big, you should be smelling smoke somewhere.

 

[badstang123]

I did have an optima red top that went bad about a week or two before this happened. The negative terminal started to rise out of the battery, which cracked the plastic around it and then acid started boiling out. I didn't know it till i heard the whining noise in my stereo. I looked under the hood and the thing was sizzling. I think this is what might have caused it.

 

[99FiveOh]

Yup! Sounds like the problem. did you get the new alternator in yet?