Dougs951S

I've been convinced I had a dying alternator since I bought my car. Cold start I usually see about 13 volts, down to about 12.25-12.5 once warmed up. Gauge also reacts to loads like brakes or windows which pull it down to just above or right on the 12 line. Cleaned all the grounds and it made no difference. Guess this is normal, either way I've noticed no electrical issues.

User 52121

Ok logged into the Windows side.....

Looking at my stack of logs here:

The very first log I took, it was in the 50s (outside air). Battery voltage seemed to hover around 13.6v.

The logs I took on Saturday when I first installed the LC-1, show ~13.3v. It was only in the low 60s for a high, and I didn't actually get the car on the road until the evening when it had dropped to the upper 50s.

Logs I took yesterday after getting the LC-1 sorted out (wasn't reading properly, had to make some adjustments per Josh) when it was much warmer out (upper 70s) show a consistent 12.65-12.72v. Note though that this was also after dark, with the headlights on.

So it seems, as the outside temp rises, volts go down (which was already established as "expected behavior" earlier in this thread). I guess I wish I had the logger back when I had the Bosch alternator to see if there was a difference.

I'll take a log again tomorrow morning now that I've cleaned the grounds and see if it makes a difference.

EDIT: In case you want to see - here's one of the logs I took last night showing the 12.6v. http://omniglh.net/951/44444.xdl

We need to get .xdl files to be added to the list of acceptable attachments here on RL.

User 52121

Ok... took a bunch of logs this morning.

Seems that voltage at the battery is ~0.3v higher than what the logger says. Otherwise all voltages listed here are what the logger reports. I have to park my car downtown and am not interested in leaving my nice multimeter in the car, so I didn't take any other readings with it after I left the house.

Battery was ~12.45v this morning before starting, according to my multimeter.

Upon cold start after sitting overnight, ~13.2v per the logger. (13.5 at battery).

Driving for 5 minutes or so, between 40-60 mph on country roads getting to the expressway... down to 12.6-12.7v.

Remained constant at 12.6 or so while doing 70-75 once I got on the expressway. Upper 60's ambient air temp.

Once I hit traffic (bumper to bumper) it fell. 12.5, 12.3, 12.1 and seemed to hover between 12.09 and 12.17 for the rest of my trip in... easily 90 minutes of bumper to bumper, 5-10mph. Gauge on dash pointed square on the line for 12. Intake air temp was in the 180-190 degree range so it was definitely warm under the hood.

Hit one free pocket in traffic about halfway in where I was able to get up to ~40mph for 3-4 minutes. Voltage started to creep back up after ~3 minutes or so, back to 12.6. Once I stopped and sat for a minute or two it was back to 12.09-12.17.

RPM doesn't seem to have any effect. Load doesn't seem to have much of an effect (fans cycled on and off like normal, maybe made 0.1v difference, headlights on or off, maybe 0.1v difference). Car runs just fine, not doing anything screwy or anything.

I worry it's going to get worse once the summer hits and it gets HOT outside. :/ With no more back seat, I don't get to drive it very often other than at PCA events, unless I commute in it (otherwise the family usually goes with me... so I gotta use the truck or the wife's car). Last thing I need is a problem while stuck in rush hour traffic.

Hey Refresh - so knowing you have a new engine harness, and have a similar issue, I'm gonna take a gamble that the problem isn't in MY engine harness. Are you still running the original battery cables? I'm still running the originals. They don't *look* bad... but maybe there is a problem lurking under the insulation (?)


PS - just gotta say... thanks to Joshua @ Rogue Tuning.... dude I love having data that I can record and replay....

blown 944

Try measuring voltage at the alternator post and at the battery when you're seeing low voltage. I have had the battery cable become resistant about 16" from the battery.

User 52121

Thanks Sid I'll try that when I get home.

I wonder if I/we are under-driving it? In eniac's thread he mentioned "using the smaller Bosch pulley"... see: https://rennlist.com/forums/4449611-post35.html I'm not clear if he did that because the stock pulley for the Nissan application is not a 6-rib pulley. I'll have to measure the dia of the two pulleys (what's on my Nissan one, and what's on the old Bosch) to see if the Bosch one is smaller.

mudbuddha

Jim- you worry too much. How does it feels when you are on boost? If it makes you feel better, I will take your OEM alternator whenever mines let go

86 951 Driver

Have you replaced your battery cables yet?

the alternator should be running about 13 volts I would think around town. Mine shows 12 volts almost constantly after the fans start running.

User 52121

I have not. But reading this post....

From: https://rennlist.com/forums/10320989-post22.html
...makes me wonder if my problem lies in my battery cables.

Mine certainly *look* fine... but that doesn't mean much! I shot Robby a PM, figure it can't hurt to put fresh cables in the car anyways. I'll also look into perhaps swapping in some new battery connectors like the quoted poster above did to see if that solves anything temporarily.

Ronin-951

Just a couple observation's, first, Lead/Acid Cells produce 2.2v, so resting Voltage should be 13.2v - are you touching the Battery Posts and not the Connector's? Like said above, any Crimp can be corroded, even a proper 12 Ton pressure Crimp, so Solder type Post Connector's are best. We are dealing with a corrosive Gas here afterall. Output Voltage of the Alternator's Regulator is generally between 14.2 and 14.5v - no matter the Amp Draw unless above 80% of the Rating [Transistor Heat thing] = unlikely. When using a Meter, always use the lowest Scale possible that covers the expected range of measurement. For my money, only a high end unit like a 'Fluke 77' gives accurate .0 readings at the 12vdc level. When measuring, use a jumper to the Lead Battery Post, not the Car Frame/Engine Block/Ground Lug/Battery Post Connector - minor point, but your looking for minor difference's. Sometimes looking for a Voltage Drop is better than looking for Resistance, use the Volt Scale and measure one end of a Wire to the other end, while hooked up and energized, looking for 0v. If you do use the Ohm Scale, always unhook at least one end of the Circuit.
P.S. Ya, sounds to me like a poor Alternator Positive Wire or Mount Connection - some depend on the Mount for the Ground path.

User 52121

I will take another reading when I get home and make sure I grab it at the posts. I'll also poke around and take some different voltage readings at the alternator.

And I am using a Fluke 88.

odb812

My voltage problems were from a bad negative cable going from the battery to the block. The insulation was all cracked up in the bend behind the intake manifold. I was checking the voltage drop between the neg post and each of the grounds while turning accessories on and off when I noticed the cable. I replaced my cables and now there is minimal voltage drop(~.2-.3v) and it doesn't drop when I add accessories, but my passenger window is still slower than the driver.

User 52121

Ok did a couple quick tests.

First it seems I have a ~0.5v difference between the dash gauge and the actual battery. Gauge square on 12v, 12.1v in the logger, 12.56 at the battery according to the Fluke after driving home.

Car sat in the garage for a few hours while I went to dinner.

Just did a few tests now after it had time to cool, formed mostly from tests I saw in other threads.

13.5v at the battery according to the Fluke.

13.5v from the negative battery to positive post on the alternator.

14.3v from positive post on alternator to alternator case.

As the car warmed up while idling in the garage, voltage at the battery started to drop (fell to 13.1v) but voltage at the alternator stayed at 14.3v.

0.1v when going from positive battery post to positive alternator post.

0.1-0.3v when going from negative battery post to various ground end points around the engine bay.

1.3v when going from negative battery post to alternator case. (!!!)

0.4 ohms from alternator positive post to battery positive post.

Sounds like I still have a negative ground issue somewhere, no? Perhaps the alternator itself isn't grounded very well?

If Robby doesn't get back to me by tomorrow AM, I'll order a set of Porsche cables. I took a look at the cables in the car much more closely tonight, and they're not as pretty as I thought they were... some of the insulation has cracks. So even if this doesn't solve the issue, I'll have peace of mind knowing they are fresh.

Have an AX this Sunday, so hopefully I'll have them in my hands, one way or another, before Saturday so I can install it then.

User 52121

FIXED IT! (Temporarily)

Thinking about the 1v+ drop from the alternator case so I rigged together two 12ga wires from the alternator case to the block. Boom. 14.3v at the battery.

About to go sit in rush hour traffic... The ultimate test...

URG8RB8

I was going to tell you to read my post from Ice Shark Cable thread. Guess I failed to mention that I also properly ground the Nissan alternator with the same type of 4 AWG cable.

PS: Anybody tell me how to link to a post from another thread?

86 951 Driver

I still have the standard alternator, but my voltage is low. I wonder if I need to get a supplemental ground or possibly just new cables all around.