Update on 120 amp Mancini alternator install = more questions:

[DocMel]

Update and history

I installed the 120 amp alternator kit on my 440, 71 Cuda.  (I have an aftermarket radio and FAST fuel injection)

The new alternator did not put out a charge:  At full battery charge and engine at idle, on my hand-held it read 13.8v at idle and got lower , and lower upon acell at 3000, and got progressively lower in voltage until it got to below 13.0 volts

So I reinstalled the old alt,  everything read great at a solid 13.8 at idle, and 13.9-14.0 volts at 3000 rpm

So I sent in the 120 amp back to Mancini for another at my cost of $21 for shipping

I just installed the replacement from Mancini.  I am completely stumped.  It reads 14.1 v at idle, and 14.0 at 3000 rpm.   I ran the engine for about five minutes, and that what I have now

Is this thing putting out a charge?    I find it hard the believe I may have another defective alt

  Heck, I even switched out the two small wires on the back of the alt to see if that would make a dif:  No change, 14.1 at idle, 14.0 at 3000 rpm

What, if anything, am I missing here?
 

[Chryco Psycho]

Battery voltage is 13.2 or 2.2 / cell x 6 cells , so if you have 14v it must be charging , it should drop to 13 v with it not running , as long as the voltage exceeds the battery voltage it is charging , sounds like you have a few accessories to run so 14v sounds right

[DocMel]

Ok  That makes sense on the surface.   Just dont want to end up on the road dead:  thats the only prob with fuel injection.  If you get low on voltage, you cant really limp home as you can with a carb

[72cudamaan]

You don't say what your batt voltage is with the key off. A sulphated plate in the battery will cause a
low charging condition also. Have you done a load test on the battery?

[DocMel]

Yes.,   did a load  test on the battery at the shop when I had an charging  problem about 3 weeks ago and went to see why my bat went low  at that time:  The bat load test listed as good, with an indicated low output at regulator (Turned out to be poor grounding at the regulator housing)

I exchanged the battery for a new one  anyhow at that time, bought a  new regulator and fixed the regulator ground at firewall and had the charging system checked again at that time:  all listed as good

Really, the only issue I have had since is trying to go to the 120 amp Mancini conversion kit     

Im thinking the only real test is to go out and drive today, stay close to the house and monitor my hand held and see if my voltage goes down to 13.0:  if it does, I still have a problem with the 120 amp conversion

I am open to any other advice out there

By the way, if one hasn't noticed, the alternator in the Mancini kits are REMANUFACTORED:   Says it right on the box it comes shipped in.  The sticker in obviously placed on the outside of the box OVER the original Denso part number so that you dont have easy acess to the actual Denso part number to order one yourself

   While I dont have an issue with certain remanned parts as long as they work, you would think they would sell new ones, not remanned:  If I missed the fact that the alts in these kits are listed as remanned on their website, Ill be the first to apologize for even bringing it up

[Haddixj]

you should be able to go to autozone or parts store and they will do a charging system test for free by loading the system.

[Strawdawg]

Sounds like the factory alternator was perfectly adequate to handle the load as the voltage did not drop.  If it had dropped substantially at the battery when the lights were on and you were getting on it, then it would have been too small.

If the first Mancini unit would not stay above 13.5v at the back of the alternator or battery, that would be a sign of a bad alternator assuming your connections and wiring was solid.

The second one sounds as if it is working as it should be.

I have not looked at the FAST specs but I have seen XFI systems working when the voltage was close to 10 volts.  I suspect you are being a bit over cautious

[DocMel]

All 

Went for a 60 mile drive, stayed at  constant 14.1 v so I believe I am ok

You bet I am over cautious:   Example: When I broke down last time because of a no charge it was on a steep and curvy mountian road here in Co with NO shoulder to pull over.  Also no cell coverage.  I had to walk about 2 miles to the nearest house, and no one was at home.  When I got back to the car I waited for about another 20 min till a person pulled over, and he took me another 15 miles to the nearest tow service:  Suck factor was really high that day

My older alternator did the job, but barely :  But nothing will work in a charging system unless all of the related components work

Really, the initial goal here on this post wasn't to get the original alt to work correctly:  I had already done that with my old 60 amp alt.   I just wanted to get a higher amp alt to push what aftermarket electronics I have on the car now,  and the original 120 amp Denso alt from Mancini did not work

Lets be honest:  60 Amp alts dont work well with all lights on on stock car to begin with, especially at WOT.  Adequate, yes,  but as good as it could be, no way

I would recommend to anyone  to go with a higher amp alt, period, even its a 75 amp unit

In my situation with Mancini, I just got a bad alt to begin with in their kit:  I had it replaced and all is now good

Frankly, going to a higher push amp alt makes sense,  period

One last note ref the Mancini kit:  The alt bracket kit is of high quality, very beefy and comes with all mounting hardware.  But the alternator does not come with the two small nuts to hold the two regulator wires on with
 

[Strawdawg]

No question that it makes sense if the existing alternator will not hold the voltage up.   If the voltage does not hold under load, then it means the amperage supply is low assuming that the wiring is good.    It even makes sense if you just want an insurance policy to minimize an old unit's chance of failing.  The Denso should be a better alternator with regard to longevity.  On the other hand, I have seen several new (not rebuilt) alternators that were bad out of the box and I often prefer finding a factory original that is used because of this.

I live on a ranch in the country and I understand being stranded.  I don't even like walking a mile back to my house if I break down on the place if it is 105 degs but then I am old.

Your next job is to call Mancini, ask for the boss, and ask him why you had to pay shipping to return a defective alternator that was not checked before it was put on the shelf to sell.  I bet if you are polite you will get your money back.

[DocMel]

Good points   And Ill give Mancini a call today as see if I can recoup the return shipping charge   

[Chryco Psycho]

A 60 amp alt should keep up just fine even with everything on but not at idle , after installing extra accessories you can have problems , modern alts may charge better at idle which will help but you can do that with a smaller pulley on the alt too .

[Aussie Challenger]

When I fit a new or another alternator to a vehicle I always check the voltage at idle, then increase revs  to around 2,000 and see if there is a difference, then I turn on all the accessories and all head lights, check idle voltage and then rev up again. A working alternator voltage will drop 1/2 - 1 volt with all accessories on at idle but go back up when engine speed increased if alternator is working, it is a simple test and has never let me down.