MS2 V3 running hot showing low voltage

[svocapri]

My Megasquirt2 v3 mainboard was used for about 2 years until 2010 and then sat unused until last month. Now that I have the car running again, I have upgraded to the latest MSextra code and started a new tune from the defaults. Yesterday when I drove the car, It started and ran OK but by the time I got home I noticed that the battery voltage in Tuner Studio was showing 11 volts. I checked the battery with a multimeter and it was charging at 13.5 volts and without the car running was at 12.5 volts. I then felt the Megasquirt and noticed it was hot. After letting the car cool down overnight, I checked it this morning and Megatune shows 12 volts, but once again after driving for 15 minutes it was registering 11 volts and the Megasquirt was hot.

Can anyone offer suggestions on how to start troubleshooting this?

Julian

[billr]

I would start by disconnecting the MS from everything except power and ground (and com to TS), let it "cook" for a while and see if it still heats up and indicated battery voltage drifts low.

[svocapri]

Billr,
I sort of followed your direction. One change I have made since the system was running back in 2010 was enabling idle control with the stepper motor, and this was set to "always on". Since I was going for the low hanging fruit, i changed it 'Moving only", power cycled, and let it cook. I left everything connected and powered on in the car but did not start the engine. The megasquirt did not get hot this time but the voltage did drop. After about 30 minutes I checked the batery with a volt meter and it was actually down around 11.8 volts. I then put a charger on it and let it go for an hour with the charger on it. The Megasquirt never got hot but the battery did charge up to 13.8 volts, however the megasquirt still showed less than 12 volts in tuner studio.

What should be my next step?

[Myrrhstang]

Sorry if this sounds obvious, but what's the condition of your battery? Old-ish, new, known good?

Sometimes a lead-acid battery will seem to charge to 13.8V just fine, but hit it with even a small load, and the voltage will sag...

[billr]

Check the "Vref" (5V), see what that is doing.

[svocapri]

myrrhstang, It does look like the battery is dying. I left the trickle charger on it for the last couple of days and now it won't even turn the engine over. Strangely, it seemed to work fine before I put the charger on it. I'll get a new battery and then see what happens.

Julian

[svocapri]

I finally got back from the west coast and am working on my car again. I put a new battery in and drove it today. The Megasquirt showed 14.2 volts immediately after starting and was showing 12.2 after about 15 minutes of driving. The voltage at the cigarette lighter was reading 13.9v when the Megasquirt was showing 12.2.

What are some good points in the Megasquirt to check the 12 volt rail with a DVM?

Julian

[billr]

First, check it on the mainboard-side of the DB37 connector, pin #28; let's see what is actually getting to the MS.

[svocapri]

I just tested this morning. I started the car, and at high idle it was showing 14.2 volts at pin 28 while TunerStudio was reading 13.8. After idling for about 15 minutes around 750rpm, pin 28 was reading13.8 while TunerStudio was reading11.2.

What pin on the socket does megasquirt II use for its 12 volt reference?
What should I check next?

Thanks,
Julian

[billr]

Check the "Vref" (5V), see what that is doing.

That is on the DB37 pin 26. Also, check voltages on both legs of D10. MS "reads" the 12V at the junction of R3 and R6, pin 1 of H1 (the bootloader jumper/header); but it isn't reading the 12V directly, it is reading a fraction of the 12V due to the resistor-divider formed by R3 and R6.

[Matt Cramer]

Can you take the lid off and check what location on the MS2 seems to be the hottest? Also, will the board become hot if you have the key on and engine off, or only if the engine is running?

[svocapri]

I finally got some time to open up the megasquirt and do some testing. Here is what I have found so far.

After sitting for a few days, and with the MS2 processor removed from U1
Battery Voltage 12.56
5volt at Proto Area 4.98
D10 Left Side 11.63
D10 Right Side 12.34
R3 Top 12.35
R3 Bottom 2.004
R6 Top 0.00
R6 Bottom 2.002

MS2 processor installed and engine running
Battery Voltage Forgot to measure
5volt at Proto Area 4.92
D10 Left Side 13.27
D10 Right Side 14.09
R3 Top 14.13
R3 Bottom 2.167
R6 Top 0.00
R6 Bottom 2.162

After driving into town and back (About 30 minutes)
Tuner Studio 11.2
Battery Voltage not measured
5volt at Proto Area 4.91
D10 Left Side 12.89
D10 Right Side 13.71
R3 Top 13.72
R3 Bottom 1.839
R6 Top 0.00
R6 Bottom 1.846

The temperature of the MS2 processor after the drive was about 158 F and the heat sink with all the transistors etc was below 120 F.

Julian

[svocapri]

I forgot to mention that I have a ceramic capacitor installed in H1 due to some noise issues I had as a result of the 4x TBI low-Z injectors. I may try removing this to see if it is leaking voltage as it warms up.

[Six_Shooter]

Do you have a good soldering iron?

From the testing you have done, my first idea would be to inspect, and re-solder the connections at R3 and R6. There might be a poor solder joint in one of them (I would suspect R3 myself) that might be causing a voltage drop more across it than should be. Replacing the resistor might also be a good idea.

With 13.7V at the top of R3, the output voltage from the divider circuit should be almost 2.3V, you're nearly half a volt lower than that.

[billr]

What value is the cap at H1? (A subtle way of asking: are you sure it is ceramic and not tantalum?)

[svocapri]

BillR, I believe your suspicion is correct that it is a tantalum capacitor. I will remove it and test again.

Six_Shooter, I will check those solder joints and re-touch them.

As a side note, my old Innovate LC1 has been reading rich. while showing 13.5 AFR the plugs were paper white. I have to boot a windows machine to check and see if the AFR meter is outputting what the Megasquirt is reading or if there is a difference.

Thanks for help diagnosing this so far.
Julian

[svocapri]

Billr, the capacitor in H1 was backwards. It is now removed I'll run it again and see if that was it. I did re solder R3 and R6 just for good measure. The pic is the cap from H1.

[svocapri]

I drove the car for over 30 minutes and the voltage in tuner studio only ranged from 13.8v to 14.2. Looks like the capacitor was the likely cause. Now I have to track down the AFR discrepancy.

Thanks to everyone for the help with this.

Julian

[Six_Shooter]

Capacitor in H1? I have several V3.0 boards here and nothing is in H1 in them, other than I think one has the pins installed, but certainly no cap.

[WillExoIX]

Ill have to take a look at those resistors on my board as I have a similar issue with voltage dropping in the MSDroid readout on the Android head unit, but battery voltage checks out.

Haven't noticed if the unit gets hot ill shoot it with the IR gun next time I go out on a tuning run. Currently dealing with starter issues with the new 3.4 setup, though it might be related to the VATS bypass from the PO.

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