battery voltage display in the main dashboard

quick65 · #1 (**permalink**) 01-06-2010, 06:48 PM

when my car is running i measure 14.8v at the battery, about 14.6v at the fuse on the switched 12v supply lead going to the ecu, but only see 13.4v (at best) in my dashboard display on the c-com software. is this typical? how would i go about changing this in an attempt to see the propper battery supply voltage that is being applied?

TurboNova · #2 (**permalink**) 01-07-2010, 12:30 AM

Are both the power and grounds for the ECU directly to the battery?

quick65 · #3 (**permalink**) 01-08-2010, 01:28 AM

yes, both go directly to the battery. like i said, the voltage reads good all the way up until it enters the ecu. at the 12 switched lead after the fuse as it leads into the ecu i have
14.4v, but in the software it displays as 13.4v and thereby provides calibration correction due to the low voltage condition.

TurboNova · #4 (**permalink**) 01-08-2010, 01:26 PM

Have you unplugged the harness connector from the ECU and checked the voltage at the pin on the ECU?

quick65 · #5 (**permalink**) 01-09-2010, 08:25 AM

no i haven't, but i have checked it on that side of the fuse which is only about a foot away from the ecu...so my thinking was that if that foot of wire has enough resistance to be dropping a full volt across it then it would probably make a good heater. lol. i will check it with the volt meter first thing this morning just to be completely sure though. if it were a bad connection the voltage would be erradic but it is very stable. what do you guys see for a voltage in your F9 dashboard vs. your voltmeter on the dash?

quick65 · #6 (**permalink**) 01-12-2010, 01:41 AM

ok. so i measured the battery voltage with the car not running. it was 11.8v at the battery and 11.4v at B17 and B18 with the connector unplugged. i wasn't able to monitor the voltage in the fast main dashboard because the connector was unplugged. but since i was seeing more than a full volt difference and now i have measured the line loss to be
0.4v, that would leave a remaining voltage loss of greater than 0.6v within the ecu, or that the ecu is reading the voltage differently than my fluke 87 meter as well as my autometer guage. where do i go from here?

quick65 · #7 (**permalink**) 01-13-2010, 01:42 AM

also, in verifying my wiring i noticed that pins D3, D5, D6, D8, D10, D12, D15, as well as
B25 are all ground leads that are not installed into my harness.

TurboNova · #8 (**permalink**) 01-13-2010, 02:02 AM

That's normal for a GM TBI (actually generic harness)

quick65 · #9 (**permalink**) 01-14-2010, 05:18 AM

thanks brian,
today was a nice day so i was able to actually fire the car up and drive around the block. the master dash says my voltage to the ecu is 13.9 when it infact is 14.4. is this something i should worry about?
the reason i ask is because i'm trying to troubleshoot a carbon fouled/fuel fouled plug condition i'm having. even though my air fuel mixture reads 14.7:1 my ngk 5671a-8 plugs always look dark brown or soot covered. the 02 sensor works cause i can add fuel and the reading reacts accordingly as well as black smoke is generated under acceleration. this is with 22 degrees of total timing, 116 octane fuel, and 22 pounds of intercooled boost from my F1R. i tried going to an autolite 3924 just to see if i could get the car to idle and keep the plugs tan. no deal, still dark. msd 7531 and hvcc coil. could the cam
(.742/.749, 271/281 @ 0.050" on a 115*) be preventing me from getting the motor to exhibit plugs as a normal 9.5:1 motor would at idle?

TurboNova · #10 (**permalink**) 01-14-2010, 01:33 PM

The voltage is fine don't worry about it. What is your initial timing where it is at idle? Is this setup set up for sequential or bank to bank? The cam is fine. It could be your accel enrichment is too hi. It could be also your VE table just needs more work.