Board voltage

[PierreL]

Hello,
i have a problem with un-instable lambda readings (i wrote a post here: http://www.msextra.com/forums/viewtopic ... 34&t=55479 )
So i'm trying to see if everything is correct on my board
And i did measure the voltages on my MS2 extra board and i found the following:

On pins 20,1,31 i have 4,66v
On pin 16 & U5 i have 10.64 v (My battery is 12,10v)

My questions are:
- What can be the reason of voltages below 5v ?
- Can these low voltages be the reason why i have "jumping" AFR readings ?

I have a single cylinder, 1 high Z injector, sequential mode.

Thank you in advance for your help
Pierre

[Matt Cramer]

Could be something on VREF is shorted out - are those measurements on the engine, or on the Stim?

[PierreL]

Could be something on VREF is shorted out - are those measurements on the engine, or on the Stim?

Hi Matt,
I did measure it with the vehicle battery connected.
Does it answer yor question ?
Many thanks,
Pierre

[Matt Cramer]

Ok. Do you get the same voltage if you test it on a Stimulator? This will rule out a problem with the wiring harness.

[PierreL]

Ok. Do you get the same voltage if you test it on a Stimulator? This will rule out a problem with the wiring harness.

Not at this time Matt.
I will try next week.
But i do not think there is a problem with the harness: we did buy it from DIY Autotune
Nevertheless, i will try !
Thanks,
Pierre

[DaveEFI]

Don't forget the grounding too when searching for voltage drop. There will be a slight drop on the MS 12v rail over battery volts since there is a series diode. Which drops approx 0.6V. But the 5 volt rail should be near enough 5v regardless of battery volts. If it's not, as has been said, chances are there's something drawing too much current from it.

[PierreL]

Thank you Dave,
I've just tested it with the stim.
See my reply to Matt here below...
Pierre

[PierreL]

Ok. Do you get the same voltage if you test it on a Stimulator? This will rule out a problem with the wiring harness.

Matt,
I just measured the board voltages with the stim connected.
On pins 2/1 , 32/31, 19/20 i read 4.69 volts.
On 19/16 i read 10.06 volts.

Thank you for your help,
Pierre

[Matt Cramer]

Is F1 or the voltage regulator getting hot?

[PierreL]

Is F1 or the voltage regulator getting hot?

Hi Matt,
Sorry to come back so late, i now had the chance to measure temperatures.
So, i did turn the box on, wait a few minutes and mesured +- 35°c on F1 & +- 40°c on voltage regulator.
But the heatsink was on +- 53°c.

Does it help ?

Thank you again,
Pierre

[Matt Cramer]

If you remove F1, does the voltage regulator stop getting hot?

[PierreL]

Matt, i did lift one leg of F1, and now the temperature of U5 does not increase. It seem to stay at ambiant temp.
Good news ?
what's next ?
Many thanks Matt,
Pierre

[Matt Cramer]

Something is shorted on the 5V plane. Put back in F1 and try to rule out things on the 5V side. The most common one to be damaged is D19; try desoldering one of its legs and see what happens.