Voltage drop under heavy acceleration

[Blackbirdws6]

Figured I would post this to the wider audience. I'm having an issue with the bird where when I give it heavy throttle or WOT. The voltage drops linearly with RPM so much that if I kept my foot in it, the check gauges light will come on. If I let off of the gas, voltage comes right back and its fine while cruising. It starts to dip right around 4k RPMs and up.

Here is the current configurations.

- Mr. Alternator 200A CS144 unit
- Fairly new belt tensioner
- Brand new NAPA premium belt
- Optima Yellow Top battery

All of the connections, power, ground, etc appear solid.

The belt feels like it has very good tension at rest and I've never had this problem before. The alternator had a voltage regulator go bad which was replaced under warranty. No signs of belt slip.

Battery tested good at the local auto parts store. So did the alternator but their machine doesn't spin it up very much.

Thoughts?

[LTb1ow]

Bad alternator or its kicking something on at high rpm that is drawing a **** ton of load without tripping a fuse/breaker.

[sweetbmxrider]

Would the other fuel pump kick in around then? But I think you need an ampmeter and test under the given circumstances.

[greenformula92]

Yeah but if something else were kicking on wouldn't it go to that voltage and stay there? Not continuously drop off as the rpm's rise

My first thought was belt slip but you said you don't have any. That leads me to believe that the alternator is going bad or you have another crap regulator.

Does anyone have a known good one you can try?

[MyFirstZ]

I was thinking bad alternator again as well. Other then that a bad wire. Not the right gauge or going to visually damaged causing excessive resistance during the higher amperage.

or the gauge is incorrect.....unsure of how it gets the voltage reading. But alternator seems the most likely.

[Blackbirdws6]

I contacted the alternator manufacturer and they said it could be belt slip. I don't see any dust and the belt still looks good but perhaps this is still happening. They mentioned trying a slightly smaller belt since they fit their alternators with slightly small pulleys to help with idle volts. So perhaps its tight but not tight enough.

I did not have the issue before but I actually had a significant alignment problem so the belt rode the balancer a bit towards the rear. Maybe this created more tension which is why I never had the issue before.

The 2nd fuel pump comes on around 4 psi and I will be making around 10 at that RPM where I am seeing the drop so I don't think that's it.

Ltb1ow is going to let me borrow a stock size pulley which I will toss on the alternator and give it another shot. If that doesn't do it, I will likely just buy a unit from the local store and see if there is any change.

[LTb1ow]

Why buy another unit, I can lend you the one sitting in my heep..

[Blackbirdws6]

Why buy another unit, I can lend you the one sitting in my heep..

I did not know the offer was available. I was prefer to try the stock size pulley before I break your working alternator. :)

[Dudbird113]

My old alternator would do the same thing, replaced alternator with a new one and shes charges like a champ

[Blackbirdws6]

The alternator I have is still under warranty so I will try the pulley from Matt and if it doesn't work, I will have them replace the unit.

[Pampered-Z]

I had the same issue and the alternator needed to be rebuilt. JSP had it done for me.

[Blackbirdws6]

I had the same issue and the alternator needed to be rebuilt. JSP had it done for me.

Good info. I still think its the alternator but I will give it the honest try with a different pulley and see what happens.

[Blackbirdws6]

Swapped to a stock size pulley for the alternator and the issue appears to be gone. Pretty surprised but I will take it :). Thanks to LTs1ow for the pulley shipment!

[ThoR294]

Darn was about to say pulley size. Nice job guys :P

[Blackbirdws6]

Well, seems the issue isn't entirely fixed. Changed spark plugs yesterday and took the car out for a run. Car ran like an animal but I saw the volt drop again on one of the pulls. I'm going to message the alternator company and get this thing replaced.

[Dudbird113]

Was the other pulley you had on there smaller than the stock one?

[Blackbirdws6]

Was the other pulley you had on there smaller than the stock one?

Yes.