Idle problem

[slappinX 10+ year member]

i just installed a new 180 amp iraggi alt. It works great when i drive but when i come to a stop and a heavy bass note, I see my tach drop and feels like it wants to die but won't. My voltage is 12.8, full tilt at idle then jumps to 14.2v when i rev it. Does anyone know what it could be?

here is a video of my tach after it has warmed up. you can see it idle fine then when i turn up my music you will see it fluctuate. Is this an easy fix like grounding or is it moreso cleaning or replacing something.



dont mind the noises, I recorded the video on my mac and i was pressing buttoms and it picked it up

I have an 89 DX with DPFI. any help would be great.

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[audioarsonal 10+ year member]

Probably need a smaller alt pulley.Did you charge the batteries with a charger before installing the alt?

 

[slappinX 10+ year member]

Probably need a smaller alt pulley.Did you charge the batteries with a charger before installing the alt?

yup. the pulley is just as small as the stock one

 

[MasterOfAllBass 10+ year member]

my rebuilt alt is @ 200 amps in my 99 blazer and dose the same thing i hate it.

 

[audioarsonal 10+ year member]

What is your idle RPM?What size is the crank pulley?

 

[slappinX 10+ year member]

I idle at around 750. iraggi gave me a over drive 3 groove pully

MasterOfAllBass do you have an iraggi also?

 

[J31Rob 5,000+ posts]

I idle at around 750. iraggi gave me a over drive 3 groove pully
MasterOfAllBass do you have an iraggi also?

no. rebuilt stock alt. reading > you.

 

[jrwalte 10+ year member]

yup. the pulley is just as small as the stock one

Does your alt stay around 14 volts when you are idling and aren't blaring your music?

If so, your alt is fine. The problem is an alt outputs less current at idle. To resolve this problem you'd have to get a second battery to help stabilize the voltage.

 

[MECHMAN 10+ year member]

The electrical load increases the mechanical resistance against the crank pulley and it's bogging the motor. If you try to put one of my 250amps on most 4 cylinders, it will stall the engine because it requires aprox 11hp to turn a 250 amp unit.

The voltage is getting low because the alternator isn't spinning fast enough. Small case HO alternators typically have lower idle output than a stock alternator.

I would try increasing the idle speed to help the engine hold up to the alternator load.

 

[MECHMAN 10+ year member]

Oh, BTW I just watched the video and saw that it's a Honda.

Honda regulators have load sensing circuitry that increases idle speed when it senses a heavy electrical load on the alternator. Because bass hits place an irratic load on the electrical system, the idle speed compensation can't react quickly enough to keep the idle steady. There is not much you can do to fix that.

The good news is that Honda regulator feature is the only thing that keeps the engine from dying when you put a big alternator on it.

 

[audioarsonal 10+ year member]

I idle at around 750. iraggi gave me a over drive 3 groove pully
MasterOfAllBass do you have an iraggi also?

Well with a 750 RPM idle and assuming you have a 3 to 1 ratio alt pulley size to crank pulley size.That would only put you at 2250 alt RPM.Most alts don't start output until 2400 alt RPM.

 

[slappinX 10+ year member]

Does your alt stay around 14 volts when you are idling and aren't blaring your music?
If so, your alt is fine. The problem is an alt outputs less current at idle. To resolve this problem you'd have to get a second battery to help stabilize the voltage.

when i have my music off, its around 13.5 at idle then jumps up to 14.2 when i rev it.

Oh, BTW I just watched the video and saw that it's a Honda.

Honda regulators have load sensing circuitry that increases idle speed when it senses a heavy electrical load on the alternator. Because bass hits place an irratic load on the electrical system, the idle speed compensation can't react quickly enough to keep the idle steady. There is not much you can do to fix that.

The good news is that Honda regulator feature is the only thing that keeps the engine from dying when you put a big alternator on it.

you are saying there really isnt much i can do?

Well with a 750 RPM idle and assuming you have a 3 to 1 ratio alt pulley size to crank pulley size.That would only put you at 2250 alt RPM.Most alts don't start output until 2400 alt RPM.

what size should i go with to get 2400 alt rpm?

 

[Johnny Drama 5,000+ posts]

You need either a smaller pulley for the alt or a smaller crank pulley. The alt isnt spinning fast enough to create the current you need. If you are at 14.whatever with rev and drop at idle with no music that is your issue.

You should keep a constant voltage with no draw against the charging system.

 

[slappinX 10+ year member]

You need either a smaller pulley for the alt or a smaller crank pulley. The alt isnt spinning fast enough to create the current you need. If you are at 14.whatever with rev and drop at idle with no music that is your issue.
You should keep a constant voltage with no draw against the charging system.

i will email iraggi to see if he can send me a smaller pulley

 

[audioarsonal 10+ year member]

You need either a smaller pulley for the alt or a smaller crank pulley. The alt isnt spinning fast enough to create the current you need. If you are at 14.whatever with rev and drop at idle with no music that is your issue.
You should keep a constant voltage with no draw against the charging system.

A smaller CRANK pulley would make the problem worse.It would have to be larger.But chnging the alt pulley is much simpliar then the crank.

Also when the vehicle is running there will always be a load on the alt.