240Z, 260Z, 280Z Performance / Technical Discussions related to performance motor enhancements, upgrades.

Amp Clamp Reading

Old 09-27-2015, 03:24 PM
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Amp Clamp Reading

Hi all ,
I have a 1978 280Z pretty much stock. When I bought the car the previous owner put in a new alternator (rebuilt Hitachi) . Here are some questions/issues...my dash volt meter is pinned at 16~v. while at idle with no loads battery voltage is ~14.3V. So I throw on the amp clamp while on idle (no loads) I'm at 16-17 amps while the clamp is on Battery neg. From what I can find it is a 60amp output alternator. As I put a load on the system (lights, blower rear defrost etc) it drops to around 11 amps. The issue is some times as I'm in say 3rd gear at around 3000rpm Ill get a cutout/hesitation. I took out the alternator out of my 77 donor car ( knowing the 77 has a external regulator) my dash volt meter shows 12.5 volts, but alty light comes on. I checked the battery with the car running with my DVOM(with the original alty I bought with the car) on AC I don't have any excessive AC voltage, so the rectifier seems good. I have tested the battery with two different Midtronics systems the battery just passed a test. If possible could someone post a pic of their wiring to the alternator wiring for reference?
Attached Thumbnails Amp Clamp Reading-20150921_182532-3-.jpg  

Last edited by FrappNasty; 09-27-2015 at 03:44 PM. Reason: picture
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Old 09-27-2015, 05:08 PM
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You probably wont get much at idle. Have you tried taking a reading at say 2000, or 4000 rpm? I think the reason you are hesitating at 3000 could be due to TPS being not adjusted properly. I have the same issue at 3000, if I try to hold the throttle where I am not accelerating, but trying to keep it at 3000, it starts bucking because of the fuel cut off for cruising. Its not adjusted properly, but I haven't bothered to tinker with it because I don't ever cruise at that rpm, so really it isn't an issue for me. Does it hesitate if you just grab first gear, second, third, forth, but keep hitting say 5000 rpm?

She is gorgeous!!1
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Old 09-28-2015, 02:01 PM
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You might have a bad alternator. It should never put out that much.
How to Test a Car Alternator
You might burn up everything. The other alty needs a regulator to put out the required 14 +- voltage so your light comes on.
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Old 09-28-2015, 06:40 PM
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Thanks for the compliment on the car it is a work in progress....as they all are. So here is what I did, I had a used battery out of a VW TDI, with lots of reserve. I then adjusted the timing within the distributor (advanced the retard timing via the plate in the distributor) and I am not having any cutouts now. I'm still concerned with the amp output, I didn't mention that I also ran the amp test with loads on with higher rpms, it would climb then level out around 17-19 amps. My dash meter is still around 16v and battery at about 14.5v. This could be normal output, but I can't find any specs. But I think the alternator is weak. As far as cutout at higher rpm, none.
Also Skully, I checked out your road trip pics, we just just did a 1300 mile trip to Portland ORg. It was a blast! The car is happiest at 80mph all day. Thanks for the input guys, I'll let you know what I find. Also I lived about 5 years in Stoon, some good memories...Bud's On Broadway!

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Old 10-06-2015, 06:34 PM
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After doing some more research after checking into the timing issue, it looks like my distributor has only one hall pickup. Aren't 280z supposed to have two? Still can seem to find what sort of amp reading is spec at the battery with loads on/off, at idle and higher rpm. So if someone out there has a amp clamp and a few minutes, I would really like to see what you are getting.

Cheers.
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