In a nutshell, this is my issue:
- With an older stock alternator, I was getting some dimming of lights at a slow idle. Volt gauge showed readings that fluctuated, as low as 11 Volts, which set off a warning beep on the gauge. Coming off an idle brought voltage back up. I decided to replace the alternator, and I thought it was a good time to get a high-output model to better support my stereo. I got a 200 Amp alt from Motor City Reman.
- With the HO alternator (even with the provided 2" undersized pulley, vs. 2.5" stock), idle output has become even worse. It takes about 800 rpm for the alt to cut-in, after which it DOES perform much better than stock under high load (Stereo, defroster, blower, lights, etc).
SO
1) Is my idle speed possibly lower than normal? It looks like it settles around 600 - 650 rpm, which I've taken to be normal for a Auto Cavy. It has been suggested that I could be due for a tune up, but I didn't think the revs were unusual. There are quite a lot of vibes in my dash, but I've got aftermarket engine mounts.
2) Motor City Reman is sending me a 1.75" pulley, but I'm not sure that will completely solve the problem. Also, I was able to use the stock serpentine belt for the 2", but I doubt I'll be so lucky if I go even smaller. Do you guys think it's a sign of a poor-quality product that this should be needed? Do other HO alt users have this much trouble?
3) Failing everything else, I hope that I will shortly have an update from HP Tuners for my car, so I should at least be able to up the idle speed that way as a workaround. Any reason why I should think twice about doing this?
Thanks for any feedback.
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HO alts only increase the amps at higher rpm....like you are experiencing. they do nothing (sometime worse) at low rpm. your idle is normal for an auto.
when you had the stock alt...did you have any underdrive pullies? i have a crank pulley and my factory alt doesnt really charge at idle.
I had that issue w/ my stock alt.
It eventually totally crapped out one day. When I used my power windows, the car shut off..
I replaced it w/ a HO alternator from the same company. At idle, the voltage would be in the high 12's. The lights would still dim etc etc..
I used HPTuners to raise the idle to 900 rpms instead of 650 & all my issues were solved. The car sits around 14.5 @ idle and the lights are bright as hell.
whiteboyz24 wrote:when you had the stock alt...did you have any underdrive pullies? i have a crank pulley and my factory alt doesnt really charge at idle.
No, the pulley was stock. I'm beginning to think that maybe this had been going on for longer than I thought, and I only noticed the dimming at idle after I installed a volt gauge. It recently became most obvious now that Air Conditioning season is here, since the idle is slowest, and the full-blast blower fan has an obvious slowdown and speedup at stop lights.
RedDevil wrote:I used HPTuners to raise the idle to 900 rpms instead of 650 & all my issues were solved.
Good to hear this option should work. Hopefully they'll get my calibration decoded soon so that HP Tuners works for me.
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RedDevil wrote:I had that issue w/ my stock alt.
It eventually totally crapped out one day. When I used my power windows, the car shut off..
I replaced it w/ a HO alternator from the same company. At idle, the voltage would be in the high 12's. The lights would still dim etc etc..
I used HPTuners to raise the idle to 900 rpms instead of 650 & all my issues were solved. The car sits around 14.5 @ idle and the lights are bright as hell.
was 900 the lowest you could go with decent voltage?
At one point, the car was set to 850 rpms and it was fine.
To be honest though, I never really went through & changed it to see how much it affected voltage.
If you wanna find out what will work for you, just sit in the car and push the gas pedal just a little bit to bring the RPMS up to what you would like it to idle at. If you have a voltmeter, you will be able to tell where it has to idle to get the voltage you want.
The car is now a 5 speed, so the idle is at 900 now anyways.
Hope this helps,.
power output at idle all depends on the alt, and how it was made.
You can get HO alts, that have a decent output at idle, but most are designed for driving speed output.
Resolving my issue took both an extra-small alternator pulley (1.75" diameter), as well as a small adjustment through HP Tuners (100 rpm up at idle) . I'm still at a fringe where I can still push it with my stereo, but I could take that out with a higher idle if necessary. Voltage is nearly solid at higher RPMs, no matter what load I throw at it.
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