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Discussion Starter · #1 ·
Hi everyone.

So im having a weird electrical issue that is affecting my idle a bit. I recently replaced with an ACDelco reman alternator and it was running so clean until after my first 60 mile road trip.

Here's the symptoms.

At idle, my fuel pump is obviously oscillating causing somewhat erratic idle. The pump itself sounds like its going up and down in voltage consistently with RPM.
My lights are doing the same thing at the same rate.

I checked voltage and constant 14.8-15.9 volts at the battery while idling.
I checked all front grounds.

I do have a feeling that maybe the ground to my fuel pump is bad, causing fueling to fluctuate, causing rpm to fluctuate, causing alternator to fluctuate, causing pump voltage to fluctuate further. Does this sound plausible?
 

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How many amps is that new alternator? It’s a reman and not new? That could be an issue

Anything is possible, but do you have any OBD codes first of all?

Use a scan tool and check your live data stored Long Term Fuel Trims for me, there will be 2 different ones
 

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15.9 volts is REALLY high for a alternator to be charging. This seems off and I'd do the reading again. If your alternator is hitting charging levels of 15.9 volts, you might be over charging which could effect your electrical. PCFreak should chime in on this, I'm not sure if this is actually the case. I've always heard anything over 15 volts has potential to harm electronics.
 

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Yes going over 15 can harm the electrical system, the voltage regulator inside the alternator is probably defective,

I would get ahold of whoever you bought it from and have it exchanged.

15 & higher can damage your ecu and everything else, especially if your getting above 16 volts.

Should sit around 14.3-14.6 at idle, no higher
 

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Yes I’d stop running the car with that alternator as soon as possible before u do serious damage to a computer module and cost u serious $$$

Get a new alternator and return that thing u got
 

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140whp+15.72%= 162hp
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Mine sits at 13.8 so not good for you, sir. I did notice that sometimes my batt is at 11.6-12.4 when i start the car after not driving it for like 5-6 days but it charges up after a drive. Maybe it's time to replace my batt.
 

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Discussion Starter · #7 ·
So after a bit of reading and finding this thread
4G Electrics Flickering https://www.club4g.org/board/showthread.php?t=119959
I realized I have a bad crimp in my new ground cable I overlooked. I didn't think to check that because I usually associate bad ground with lower voltage, but it seems that the ecu can demand more power if it senses low voltage.

I'll check my crimp and go from there since the behaviour is just like in the thread I linked.

I'll update later today.
 

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Discussion Starter · #8 ·
UPDATE:

So im glad i came across the thread of dude going through multiple alternators. Mine had the SAME DEFECT. The voltage regulator on a remanufactured ACDelco alternator went out after less than 1000 miles. I had Rockauto replace it for me and she's running fine again. No weird issues whatsoever with the current alternator. I replaced it with another reman from ACDelco because I believe in the brand and their OEM for our cars. quality just goes down the drain when anything is mass produced but the 2 year/unlimited mile warranty is what convinced me.

Thanks for the replies. This case is closed!
 
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