Would an aftermarket serpentine belt cause the headlights to go dim?

 

I hate to be the *** here, but if you haven't tested both per request, then that aspect has NOT been covered...

I realize you don't have a ton of car repair experience, but I've seen many rebuilt and new alternators fail or not even work right out of the box, or within a few hours of installation...

one in particular was on a dodge colt (mitsubishi engine), I diagnosed a bad alternator (it had just had a new battery installed)... I had a tech install a new alternator and I did a VAT test on it immediately... 14.4 volts and 55 amps, a perfect read out... I had the car pulled around, charged the customer, and he drove off... 30 minutes later I get a call and he claims the car is running badly... thinking it's something else, I tell him to bring it back and we'll recheck... I do another VAT test and find 17 volts and 20 amps output... regulator on a rebuild failed...

another one, on a BMW, brand new unit straight from the dealer only output 10 amps maximum... thinking we were missing something, I spent 30 minutes making sure we didn't miss something... nope, everything appeared ok... order a second alternator, install it, wham, perfect voltage, perfect amperage...

so, just because its new doesn't mean it works...

 

Follow these pics to the conclusion.

I changed over to my back up alternator today (forgot how easy it was to swap alts on this car!)





I used my trusty home made cig plug volt meter to measure real time voltage while driving.





While in motion I get this: (13.8)


x

While stopped with the head lights and A/C on I get this: (12.3)





Conclusion..... didn't really help a damn bit. However I did notice that there were times the car idled slightly higher in gear and the voltage held great. This goes back to my initial theory that the car is idling too low in gear. It's at 675 most of the time and it should be at 750-ish to hold the RPM.

Even though I am not throwing a code, I did change the TPS recently and I am wondering if it might be set incorrectly and causing a lower RPM than what it should be in gear. Doesn't really make sense, but since I have no codes and the TPS reads fine on the tests I dunno.

It's the random occurrences of idling where it should, V/S idling roughly 100 RPM too low that have me stumped. The grounds are all fresh and new, the alt has been changed. It boils down to idle speed control while in gear now. When I first hooked the alt up it did the same thing as it always did with the old alt and I was about to just back into the driveway and quit, but after a test drive when it didn't change I had to come back for a gas card and when I restarted it was much less prone to acting up. I think this might be due in part to me disconnecting the battery. After a run or two it learns the sensors and might be setting the idle control.

Infact as I type this I am getting more convinced that since the computer just got reset I may need to wait until after a few drives to make a real assumption, but I do know that the same thing is happening with this alt, so I need to figure out a way to keep the idle 100 RPM higher or change that pulley.

Fresh alt, fresh grounds... I've done all I can do. I guess I'll just go over my VAC lines and make sure they are all tight again even though I just did it.

I also notice flashing of the "D" indicator even while at 3000 RPM if I use the turn signals though the car voltage is perfect.

 

Did you ever find a solution to this issue? I get the "D" flashing when I use the turn signals as well. Wonder if its something I should be worrying about.

 

My car is having the same low voltage issue at idle but my super afc says it is at 14.4 volts .Even my blower starts to spin slower when i turn on my headlights at idle .I replaced the battery and still have the same issues .since every ground (literally every ground) on my car was sanded and cleaned before the swap thinking its a problem with the regulator .A battery that has less amperage than recommended can also cause this since the battery plays a big part in the charging system in these cars .hope you find the bug because this is a common issue with these cars.

 

any updates?

 

Mine still flashes. It's less prevalent now that I have done pretty much everything to it I can to apply the fix. The alt change mildly helped just a tad, the new wiring and clean grounds helped just a tad. Together they made an improvement, but nothing has completely solved the issue entirely.

At the moment since all these fixes were applied, it's good enough to get by.

 

Take it to the dealer, lol.

 

this is why i hate electrical, hahaha... knock on wood.

 

have you tried getting a battery with a higher cranking amperage.
Dimming is usually not a voltage problem, its usually a starvation of amps.
I understand they are all directly related, but especially if you add aftermarket stuff or your car is just old, it sometimes just needs a bit extra juice.

You sure you haven't done anything to affect your idle, didnt you do that full time power steering thing a while back in another post, or was that someone else.

 

CCA has nothing to do with the car once on. The battery actually gets power FROM the alternator, not the other way around. The car is completely dependent on the alt and the ground while in running mode. The STARTER is the only thing that is dependent on the battery.

 

i just started having this same problem today.....

 

I understand that, but it is still in the loop. If it is not doing a great job of transfering the power from the alternator to the cells you will be effectively adding resistance into the equation and possibly get these symptoms. Think of it like a capacitor that helps deliver power during surges. A car running strictly on an alternator will not be a happy car, and will lead to premature failure of your alternator. Just trying to help you out man. As long as the cells aren't dry though you should be alright though.

 

besides the TPS, is there any other way to increase idle RPM?

 

my 96 lexus lx450 has the same problem. brand new reman alternator, tested 3 times in system, bench tested twice out of system. brand new stock battery (27 series battery @ 675 CCA) and @ idle everything dims rev up everything goes back to normal. im at my wits end here.