In my Iroc I have the stock alternator, I've been told it's an 85 amp and a 110amp, depending on the parts store I go to. Anyway, rather I'm sitting in traffic or driving, unless it's revving high, the voltage will drop from mid above 12 on the gauge to mid below 12. I have a brand new 1000 amp battery, so that's not it. I have checked all the grounds I can see, no go. When it drops I push in the clutch and rev it and it'll go back to normal, but even then sometimes it drops right back down. It also doesn't matter if I have nothing on, or the stereo, wipers, headlights, etc. HELP!

 

sounds like the voltage regulator has/is going bad..

that keeps the voltage at a steedy rate...

i had to replace the whole alternator on my moms vans becuase it was built in..

 

Have you any suggestions for an alternator? I have seen many on ebay that are 140+ amps and around $110, but the ones in Summit and Jeg's are easily $200+. I have a large sound system and plenty of other things (underbody neons, H4 headlights, etc. etc.) that pull heavy power, so I want to be sure that it isn't going to crap out on me!

 

Check the voltage at the battery with the car off. Should be 12.4-12.6 volts.

Then check it with the car running. Make sure EVERYTHING is off. Should be at least 13.8 with 14.4 being nominal.

Next turn on everything except the stereo; the heater motor to high, the A/C, the headlights, the rear window defrost, and the wipers.

It should still read at least 13.2volts. Now crank that system. At worst is should not drop below 12 volts. If it does then your system is pulling a lot of amps.

A 140 amp alt isn't always the answer. The GM regulator/rectifier is set to start charging only if the engine's above 1200 RPM. Until then it won't supply more than 40 amps. This is what keeps the thing from getting hot at idle and totally blowing up.

Unless the 140 amp alt puts out more amps than that at idle, it won't do you any good. Just make sure you look for that when you're buying one.

 

Based on what you say it sounds like the brushes are going bad. When they get worn down they tend to get sloppy in the holder and cause low or intermittent charging. The battery is not 1000 amps, it only can cold crank that mometarily. Batteries are rated in ampere/hours for normal charge/ discharge cycling. Most are in the 75-85 amp/hour rating meaning that the battery will deliver 75-85 amps for one hour before it becomes discharged. www.alternatorparts.com is blowing out new Delco OE Cs-144 alternators for about $200. It's the same unit that came on the Caprice police package and it's a good unit. I believe the CS units in 87 were either 65 or 105 amp units. Before you condemn the alt trickle charge the battery anyway, then check how it charges. If the alt is charging it's probably not a regulator. I have rebuilt quite a few and I have yet had to replace a regulator, it's either the bearings or the brushes. Keep in mind that a 140 amp unit will have less output at idle than a 105 unless you undersize the pulley. In your application a 105 amp unit should be fine. If you upgrade go with the CS-144 and not an upgrade to a 140 amp stator with the stock housing. The CS-144 has better cooling and will hold up better.

 

So, from what I am hearing, I should go to AutoZone and get a large case 110 amp?