Mach929

iTrader: (3)

i'm beginning to question whether i have an issue or not. through megasquirt or tunerstudio, what does your voltage read and how stable is it?

mine idling at 900rpm with the headlights on it jumps between 13.25v-13.75v. a continuous jump of .5v seems like a big sweep to me.

curly

iTrader: (25)

That sounds low, I think 14.5 volts is normal, which is where mine is. It jumps less than .5 volts too, I think somewhere around .25 volts, very rapidly.

Ben

iTrader: (33)

Sounds just a little on the low side. I would recommend confirming your voltage with a dmm on the battery before doing anything further, but it might be new alternator time. Your ecu doesn't have any control over this.

curly

iTrader: (25)

Ok scratch that. Just cause I'm a nice guy, I went out and checked. At 900rpm I was getting 14.00volts, jumping up to 14.2 for a split second every 1-2 seconds. Didn't change at all when I turned the lights on.

Mach929

iTrader: (3)

at the battery 14.22-14.23 stable

here's a random log, they all have always looked like this

curly

iTrader: (25)

Well I was about to check mine and compare, but found 12.6 volts :( My poor altima red top has been through a lot. 6+ years old and when I still had a radio, I'd listen to it while I worked on the car, including months of rebuilding the engine, recharge the battery, repeat. Even so I'm getting higher voltage in TS :P

Ben

iTrader: (33)

Well the charging system sounds solid then. Maybe you have an ecu ground that's a little unhealthy.

Mach929

iTrader: (3)

yay wires not my strong point

stranges12712

iTrader: (1)

Was it cold or warm. When its colder the alternator works harder and chargers the battery bet 14.2-14.5 when its warm usually 13.7-14.1

Mobius

iTrader: (2)

My scangauge normally reads 14.5 with the engine running.

Mach929

iTrader: (3)

it was about 50 degrees out. looking at some other's logs mine actually isn't far off though i'd like it to be cleaner, i'll clean up a couple grounds, if it doesn't help oh well the car runs fine, or with any luck it will burn to the ground

Braineack

iTrader: (62)

Ben or Matt or Jerry, is this something the 3700uF cap might help?

WestfieldMX5

FWIW Megasquirt adjust certain parameters (like injection opening time, ignition dwell etc) according to battery voltage. If your battery voltage is 14.2V and your MS thinks it's 13.2V I suggest adjusting the MS voltage divider so that MS reports 14.2V as well.
Battery voltage is determined with a resistor voltage divider to bring the 12 volts down to under 5 for the CPU to convert. R3 (50K) and R6 (10K) form this voltage divider. These are both 5% tolerance resistors and in my case, the ratio was 5.22 instead of 5, causing similar differences between actual and MS values for battery voltage. I swapped the resistors out for 1% values and now it's much better (0.2V difference). If you're paranoic, you could replace one resistor with a trimmer and adjust that to the exact voltage.
$0.02 etc.

Ben

iTrader: (33)

Probably not--though it also wouldn't hurt anything.

Braineack

iTrader: (62)

regarded the flux, not the voltage drop across the battery and MS...

Ben

iTrader: (33)

Yes, but I'm kind of worried that the flux is caused by a bad ground rubbing around.