niteshade247

As some of you might know I picked up I nice little tool. Well tonight it picked up a drop in voltage in the ECU just as I went to stop in the driveway tonight. Now I haven't set this part of this tool yet but it said "warning ECU voltage low average voltage 15.4 low voltage 14.2" is this normal or not? This is the first time in the week I've had this thing pluged in that it's said this. No CEL is showing with this so I'd like to know from some of the more experienced people do I need to be concerned?

RIWWP

iTrader: (2)

Are you saying it alerted at 14.2v? If so, it needs adjustment. You shouldn't be hitting 15v at all, normal running should be 13.0 to 14.9.

niteshade247

Yes it is factory set to report anything lower than 14.2v. I'll set it to pull up the live data on it and watch it for the next few days. Thanks for the info.
There is a lot on this tool and I haven't had time yet to set it all up. Got some days off coming up think I'll do it then so I don't have any more WTF moments.

RIWWP

iTrader: (2)

Yeah, warning low at 14.2 sounds odd. Cars run on a 12v system, and alternators typically put out around 14.0-14.5v, with the ECU and everything set to work down to about 11v. 15v is too high on every car I've ever dealt with voltage issues on. My MSM runs at 12.7 to 13.9, i RARELY even see 14.0v, and my ECU will start shutting down components to protect them at 15v because of overvoltage risks, and shut itself down at 15.5v (which would shut off the car and prevent the overvoltage)

Granted, I never dealt with a voltage issue on the RX-8 and am not 100% sure of it's target voltage range, but I can't believe it is supposed to be north of 15v.

niteshade247

Yea I'll set a gauge up to watch the live data and let you know what I see.

9krpmrx8

iTrader: (46)

I had my alternator overcharge and do almost 3k in damage (ABS modulator, boiled the battery, etc.). Check it out properly. And you need to calm down with this Ultragauge, this is exactly why Mazda doesn't put pin point accurate gauges in the car. If they did, people like you would be visiting the dealer every other day.

Legot

iTrader: (1)

^Accurate.

Before you try to fix anything, use a multimeter to check the actual voltage of the battery. The OBD reading of standalone readers (not bluetooth or wireless readers) doesn't use the OBD reported voltage (weird, right?). Most measure the voltage directly supplied to the OBD port through one of the pins.

There's usually a decent voltage drop between the system and the OBD port, and it's possible that your ultragage is overcompensating for that drop in an attempt to be more accurate (which isn't necessarily possible for similar reasons to the fuel level). Less likely, inaccuracies can come about using this method because once that voltage is in the reader it has to be sent through an ADC, and who knows how accurate the onboard one is.

niteshade247

Sorry there 9k but it just shocks me that mazda would put such bad gauges on a car that has such low tolerances to changing heat/pressures. If mazda would have put more accurate gauges yes more people would have rushed off to the dealer instead of cooking or blowing a engine then limping or towing it to the dealer. Thanks again RIWWP for the info found out it wasn't the ECM that's the problem my Batt is starting to die. I think the sudden cold snap here is killing it.

RIWWP

iTrader: (2)

How is a failing battery causing your alarm to come on at a perfectly valid voltage?

Legot

iTrader: (1)

Magic

9krpmrx8

iTrader: (46)

niteshade247

I noticed a drop in all voltage across the bord this morning at startup and when exiting the Hwy. Tested the batt and it's low. The drop is only happening when the RPMs drop after being on the Hwy so it could be my alternator it going out and slowly draining the batt. I did notic yesterday morning on startup she acted like she was going to flood for the first time ever sense ive owned it.

RIWWP

iTrader: (2)

Ok, glad you are fixing the battery....why are your gauges reporting wrong to begin with?

niteshade247

Because I haven't had time to set all the reporting points on the gauge yet and it seems factory settings are realy high but if not for it going off like it did I might not have checked anything and ended up flooding her on a cold morning and being stuck with a dead batt. I've got tomorrow off and will be going through the hole thing and set it all up to the specs of the car so I shouldn't get any more false warnings or incorrect warnings.