MSefi.com read only forum (Jan.15,2018)

when I power my ecu from the stim, 14.25vDC is applied by my ac/dc box per my dmm across +/-of the stim, but tuner studio only shows 13.1/ 13.2 v. u5 has an input of about 12.5 and an OPut of 4.98. I'm scared to test any of the pins on the IC cuz I don't want to harm anything by an accidental cross. I need to get this poop figured out NOW!!! any help would be great. IM SO CLOSE!!

Dave

GraffixWB wrote:when I power my ecu from the stim, 14.25vDC is applied by my ac/dc box per my dmm across +/-of the stim, but tuner studio only shows 13.1/ 13.2 v. u5 has an input of about 12.5 and an OPut of 4.98. I'm scared to test any of the pins on the IC cuz I don't want to harm anything by an accidental cross. I need to get this poop figured out NOW!!! any help would be great. IM SO CLOSE!!

Dave

14.25v is an odd figure, so is that the off load voltage? If so, loading it could easily pull it down, if an unregulated supply. But the MS should be happy with anything over about 9v. 4.98 is fine for a 5 volt regulated rail.

this is from my ac/dc until . 12v .750A is the rating. Its odd cuz its the closest I had off hand to replicate driving voltages. its about .5v high, but I wanted to see is the gauge matches the battery reading. it doesn't. it seems the ecu is seeing less than it should. I have big injectors and DO NOT want to tune around anything. I already cant tune idle correctly,,

Stick the DVM probes onto the bootloader pins and measure that voltage. Multiply by 6 and the result of that shall be equal to the voltage on the 12 V supply into the MS.
However.
If you have a 12 V supply with ripple on it , the DVM and the MS may very well show different results

Try powering the bench setup with a lab grade pwr supply or quite simply a 12 V car battery , but make sure to install a 2 A fuse directly at the +terminal of the battery.

When powered by a clean DC MS and DVM shall read the same.

Heribert

GWB,

In addtion to what others have said, it's worth noting that the power is 1/6th of the actual supply due to 2 resistors (R3=50K and R6=10K) that form a voltage divider. These bring the voltage supply into the 0-5V range that the processor can measure. However, these resistors have tolerances (usually up to ±10%), and this affects the measured voltage if these resistors are not exactly to specification.

Nothing will be affected significantly by the slightly low reading. However, if it bothers you, you can find different resistors for R3 and/or R6.

Lance.

I also get this effect when I'm connected to my car. is reads 11.8-12.0v on tuner studio and 12.6 at the battery (lil dead after sitting all winter)alternator brings it up to 13.1/2, where is should be if v levels were .6-.8 higher like they should be...

just bench tested it with a motorcycle batt. 12.79 on batt. 11.7 on megatune and tuner studio. d'oh! guys! I'm JUST learning this stuff so i'm having trouble diagnosing it myself

GWB,

You don't have to diagnose it yourself, I described the problem and solution above. To repeat, you need to adjust the values of R3 and R6. You can do this by searching through some resistors with a ohmmeter to find values where R3 is exactly 5 times R6, then swap these into the main board.

The slightly lower voltage at the 12V side of the regulator is due to the diode D10 in the path, it lowers voltage by about 0.7 volts, so what you see is normal.

I don't know how I can be any more clear than that, so I won't really have anything more to say...

Lance.

THX!