battery voltage vs scanmaster readings

[challengermike]

My scanmaster shows my battery volts to be about .5 to 1 or more volts at times less than what the battery is.I have checked it at the alt and battery and they seem to be .1 to .2 volts with in each other.Is this something i should be worried about?I thought the alt was going bad because at night with the cooling fan running and the lights on it was reading 12.5 down to 11.9 on the scanmaster,but the alt and the battery never showed less than 13.9
Now i dont know if this is related or not but ever since i bought the car and put it together the o2 readings have never been right at wot.The most i have seen is 656.And i know its wrong because if i richen the fuel up threw the chip it will run so rich at wot it blow alot of black smoke(yet no increase in the o2 readings(656)
Do you think that i should worry about the scanmaster voltage

 

[mikestertwo]

My scanmaster shows my battery volts to be about .5 to 1 or more volts at times less than what the battery is.I have checked it at the alt and battery and they seem to be .1 to .2 volts with in each other.Is this something i should be worried about?Do you think that i should worry about the scanmaster voltage

The voltage read on scan tools is not battery voltage, it is ignition voltage. What you are seeing is voltage drop in the wiring. This is normal. As far as your O2's reading low you could have a bad ground somewhere or the O2 sensor is bad.

 

[Pronto]

How are the CCs when driving around?

 

[challengermike]

ccs are moving.they scroll decently fast.

 

[Pronto]

Probably start with checking the battery. Don't overlook the wires, they can look good but be corroded inside the sheath.

 

[Steve V]

Had one here last week, with new alt,battery,cables,new grounds,new fuseable links. Showed about 1-1.5 less at the scanmaster.

Batt and alt were the same. I am figuring voltage drop at the ign switch or somewhere in the circuit.

It was a fresh rebuild and it was running well at the time. I have read/heard about this before.

It's the 1st time I actually seen it after about 7 TR's of my own plus a few friends/customers.

 

[Razor]

Scanmaster reads voltage the ECM see's on its ignition input.

Battery-starter, starter-fusible link-fusebox, fusebox-ignition switch, ignition switch-ecm. Thats a lot of wire and a lot of connectors.

 

[challengermike]

I am doing an alt test tonight,i have already checked the ecm fuse and that has the same voltage as the battery,i have also checked the connector on the ignition switch and it seems to be ok,but i have not pulled it apart yet to check the condition of the terminals.i did try wiggling it and there was no change on the scanmaster volt #s.

 

[Razor]

Did you check voltage at the Ign input to the ecm. Not the battery input to the ecm.

 

[challengermike]

I can check the voltage at the ecm,got side tracked tonight buy somebody needing there car fixed.However i did do a load test on the alt and it is weak.If i load it to any thing above 60 to 80 amps it drops to 10.5 volts.So i will have it rebuilt and see it if effects the scanmaster #s.

 

[A2000RICH]

My scanmaster shows my battery volts to be about .5 to 1 or more volts at times less than what the battery is.I have checked it at the alt and battery and they seem to be .1 to .2 volts with in each other.Is this something i should be worried about?I thought the alt was going bad because at night with the cooling fan running and the lights on it was reading 12.5 down to 11.9 on the scanmaster,but the alt and the battery never showed less than 13.9
Now i dont know if this is related or not but ever since i bought the car and put it together the o2 readings have never been right at wot.The most i have seen is 656.And i know its wrong because if i richen the fuel up threw the chip it will run so rich at wot it blow alot of black smoke(yet no increase in the o2 readings(656)
Do you think that i should worry about the scanmaster voltage

you said in your first post that the alternator never showed less than 13.9--------that means that its not the alternator.........RC

 

[challengermike]

I had the alt tested and it tested fine off the car.I also had another alt a 12si and it tested good also(better than the orignal at low rpm amps)so i put that one on the car.And its still the same as before.So i guess its time to start looking at the wires.Where should i start at the ecm or trace it back from the alt?I also didnt know if there could be a problem with the alt light,it seems to work normal,key on lights up running go's off.Also if someone has a wiring diagram that they could post it would help alot.

 

[mikestertwo]

The voltage read on scan tools is not battery voltage, it is ignition voltage. What you are seeing is voltage drop in the wiring. This is normal. As far as your O2's reading low you could have a bad ground somewhere or the O2 sensor is bad.

You don't have a problem with the voltage reading...move on. Concentrate on the low O2 issue. Check grounds....replace O2 sensor...ect.

 

[challengermike]

would'nt that be low for a ignition voltage?sometimes it drops to 11.9.Im just questioning it because it seems most people dont have this happening.I know my gn i had a few years ago never read that low.If it is correct thats fine,I guess i just need some more convincing it is ok.

 

[mikestertwo]

11.9 volts is low. Are you running a small diameter crank pulley or stock? Is this voltage reading at idle? Does the voltage increase with rpm?

 

[TurboBuRick]

would'nt that be low for a ignition voltage?sometimes it drops to 11.9.Im just questioning it because it seems most people dont have this happening.I know my gn i had a few years ago never read that low.If it is correct thats fine,I guess i just need some more convincing it is ok.

I think more are like that than you know.

The addition of accessories to the fuse panel are the main culprits. Old wires, bad grounds and even a bad ignition contact can all contribute.

Best to do is start removing accessory load from the fuse panel.

 

[challengermike]

As far as i know the pulllys are stock.Anytime a load is put on it(cooling fan,a/c or lights it drops alot.Then when you give it gas it will come up some maybe to 12.5 to 12.9.but it will never recover to the 14 to 14.5 range untill all is turned off and it is run for awhile without them on.Even with just the fan kicking on it will drop to 13. to 13.5.It just seems to me that it should pick the voltage up when it requires the extra amps.maybe not to 14.5 but i would think it shouldnt go below 12.5.

 

[challengermike]

Also i just tested the A6 wire at the ecm.It reads almost the same as scanmaster but it seems to react quicker than the scanmaster.So the meter was showing what #s would be coming up next before the scanmaster would display them.Only about 1-2second delay.So where does this wire come from the module?,i can test it there.

 

[challengermike]

I just remembered that i could have an underdrive pulley on the car.When i put the car together 2 years ago i had to use a shorter belt,its a carquest K060605.But i would think it would only affect it at idle correct?

 

[challengermike]

OK,i checked the grounds at the ecm.i used the chart on vortecbuicks.A12 was KO .01 R .04,D1 was KO .01 R .04,D6 was KO .17 R .05,D10 KO .01 R .04,D12 was KO .03 R .02.

I also checked C16 battery voltage
12.16 key off
11.8 key on(cooling fan was running though)
13.8 running (with coolong fan running)