Voltage difference between TS and applied voltage

[redmist]

I have my MS3X isolated in the car at this time as I rewire the car completely. I hooked the MS3X Ignition (red) and all grounds (10 total small wires from Main and X) leads to a power supply that supplies 13.75 volts. With that switched on, all my sensors work... Good stuff!

However, I am seeing a large voltage discrepancy in Tuner Studio.

Here is a picture of my volt meter reading right off the power supply terminals, and also the TS reading. The leads to the MS3X are only like 3 feet long.

Any ideas??

[radial]

My personal experience, as a novice user:

Just calibrate battery voltage in TS to match your voltmeter. Mine was off by 1,3v after the install (measured at the plug on the MS). Corrected it in the calibrations.

It's important that it reads correct between 11 and 16V where MS is compensating for example coil dwell in reference to measured voltage.
Outside this working area, is not so very interesting. Rather than an "indication" that you have a severe "electrical problem" if you fall down to 9v or passing 20v.

[redmist]

I played with the ADC counts for battery voltage a bit, its set at 0, and 29 right now (stock settings) however getting it to be the same voltage as things change is the issue I see cropping up. I can play with the counts, and get it to register 13.75 volts no problem.... but if I plug in my STIM using the 12 Volt adapter, then it;s not accurate as well.


If that makes sense.


I am marveled at how awesome the MS unit is, but equally amazed at how it can't determine correct voltage on an input.

[slow_hemi6]

12v adapter? is that a regulated 12vdc adapter? did you check the actual running (loaded) stim voltage with your multimeter and compare to TS guage? An unloaded and unregulated 12v adapter could be putting out 16v, I have seen it before.

[redmist]

Yes, a standard wall wart... I checked it with my Multi-Meter as well, it was dead on as to what it said it's output was to within .01 volts. Same with the large power supply in the pictures. TS Always reports an over voltage, when given a known voltage as an input.

[kaeman]

Did you check the voltages under load with the ms unit on or just check the voltages at the plug? Did you try a different voltmeter? I use fluke meters because they are very accurate, I have a couple of the cheap ones and they read a different voltage from each other. maybe the meter isn't calibrated any more. if you calibrated the voltmeter in ts then it should read the same voltages that you get with the voltmeter. remember that the coating on the board will affect your readings also. I found that the tuner studio gauge was pretty accurate, I was checking voltages and my dash voltage gauge(autometer) reads about 2 volts higher than actual vehicle voltage measured at the battery, the ecu and the alternator. all of which were within a tenth of a volt of each other using my fluke and the ts gauge was within a tenth of a volt for the fluke meter readings.

[redmist]

Did you check the voltages under load with the ms unit on or just check the voltages at the plug? The MS Unit was on, and hooked to my laptop, and my power supply and that's it. Did you try a different voltmeter? I use fluke meters because they are very accurate, No, the voltmeter in the picture is a good solid meter that I have varified voltages on. It's good... In fact it's showing exactly 13.75 V in the picture, and that just so happens to be what the power supply output is listed as. I have a couple of the cheap ones and they read a different voltage from each other. maybe the meter isn't calibrated any more. if you calibrated the voltmeter in ts then it should read the same voltages that you get with the voltmeter. I can make it read the same voltage in TS via calibration as long as the voltage stays at that voltage. For example.... I can play with ADC to make it say 13.75 Volts in Tuner Studio and Woohoo!!!!! It's fixed!!! Until that voltage goes away from 13.75, then it drifts farther away as voltage changes. remember that the coating on the board will affect your readings also. I have yet to take any readings off the board. I found that the tuner studio gauge was pretty accurate, I was checking voltages and my dash voltage gauge(autometer) reads about 2 volts higher than actual vehicle voltage measured at the battery, the ecu and the alternator. all of which were within a tenth of a volt of each other using my fluke and the ts gauge was within a tenth of a volt for the fluke meter readings. This is my desired outcome... And also why I am posting for a solution, or guidance on where this MS Unit could be messed up at.

[billr]

What does the MS 5V read with your meter, while you are seeing that difference?

[redmist]

Will check the 5V tonight.

I am going to setup the MS3 on the bench, and power it through the STIM to better diagnose the deal here.

Standby!

[redmist]

Ok,

MS3X On my desk, and being powered by a 12Volt regulated Wall-Wart. Tested voltage with meter at plug = 12 volts

Switched on I read 12 volts at power header for Stim, 11.2 volts at ground/12V header on Stim, and 5 volt Ref shows 4.89 volts Tuner studio reports 10.80 volts at default ADC

Changed ADC to 00 low, and 33 high

Tuner Studio now shows 12 volts, I read 12 volts at power header for Stim, 11.2 volts at ground/12V header on Stim, and 5 volt Ref shows 4.89 volts

So now my TS Matches what I know is being fed to the MS3X, but I get 11.2 volts when probing the headers on the stim. 5 volts V-Ref stays solid at 4.89 volts....


Now for a test.... My wall wart can be switched to 9Volts

I switched it to 9volts, Tuner studio reported 9 volts, 5 volt V-ref was still at 4.89 volts, but probing the headers shows 8.5 volts.


So what voltage am I trying to match?? The internal voltage of the MS3X as read on the STIM header??? Or the known voltage I am feeding it?? Also what is the best way to change it to match?? Using the low ADC? Or high ADC??

[kaeman]

Tuner Studio now shows 12 volts, I read 12 volts at power header for Stim,

If that is the header that the ms3 plugs into and you are getting the same voltages, then I would guess you have it set, because you are trying to reference the incoming voltage from the vehicle.
But if the 11.2 volt reading is what you are getting at the ecu connection then you want to match that number...

[DaveEFI]

The V3 board has a series diode in the 12v rail to protect from reverse voltage connection. That will drop approx 0.6v. I dunno if the software compensates for this so TS should read input volts rather than true rail volts. I think the JimStim also has a series diode for the same reason.

Is your 13.8v PS a SMPS? Could be it's producing high frequency noise which is confusing MS in some way. A scope on its output while under load should show.

[billr]

What is the precision (tolerance) of those two resistors in MS used to measure Batt V? I have never considered that function to be a precision instrument, just an indicator for when the engine is cranking and a check for failure of the charging system and general battery state.

[DaveEFI]

I have an accurate volt meter looking at battery voltage all the time the ignition is on. TS readout here is consistently 0.2v high.

[redmist]

Should I open the MS3 and probe it from some points on the inside???

From what I have gathered, my 5volts REF is "In spec" and looks to maintain that even with a given input of 9volts... So I assume it is working as needed. I guess where I see a potential problem, is that if I match voltage via the ADC count in Tuner Studio, I see a change in fueling. It's small, but it's a change all the same.

So the ultimate answer I guess, is what is more important to match?? Internally registered voltage in the MS3??? Or simply applied voltage at the connector of the MS3??

Because in my case, they are different by almost .8 volts.

[Nitroking]

My MS2 also is at 4.89V solid.. I was also curious about it.. I'll be watching the topic..

[Nitroking]

Measured on a friend on Saturday. Voltmeter on the battery shows 14.95-15.00, TS reads 14.5-14.6.. Wtf?

[Matt Cramer]

That sounds like a small - and not completely unexpected - voltage drop in the wiring.

VREF in the 4.89 range is not uncommon. There's a small drop through the F1 fuse.

[Nitroking]

The thing is that a sensor that is 0-5V for example a Kavlico 3.5 bar Map sensor I have shows wrong values. I guess this is caused because there is always this 0.11v difference.. Is there a way to make it work accurately? I mean how should I input the values for it in the calibration menu?

The sensor values are like:
0 volts -20.95 psi
5 volts 41.55 psi

and the formula pressure = 12.5 * voltage - 20.95

Now that it will never reach 5v (Vref is "wrong"), what changes are needed?

Thanks a lot!

[Matt Cramer]

The ECU takes the VREF voltage to be full voltage and scales everything relative to it. So having a slightly low VREF will be factored in.