Extremely High Voltage 25V+++

[trconn]

RUNAWAY VOLTAGE!
New to Megasquirt. This is my first post.
Something is fried and I don’t know where to look.
I’m getting extremely high voltage (over 25v)
Engine starts kinda’ normally – it takes a couple of cranks.
Initially it runs and warms up pretty much as expected. After about 3-4 minutes the volts start to rise and will continue to do so until it pegs the gauge in TS.
Of course this plays havoc with all of the settings and the engine will die a lean death.
I can keep it running, but am afraid of doing more damage.
I get the same result when I run the engine with the alternator disconnected. I had the alternator checked and it is fine.

Volvo B20F, Bosch 38lb injectors @ 40psi
MS2/Extra 3.4.2, registered
Tunerstudio MS 3.0.10
Fuel only – firing off of coil negative
I have tried this with both narrowband and wideband sensors with the same result.

I’ve searched this forum and beyond without any luck.

TConn Hi Temp.msq

TConn HiTemp.msl

[turbo conversion]

Did you disconnect the positive lead going to the alternator or just unplug the field wire?

If you just disconnected the field wire try disconnecting the positive wire and see if that makes any difference.

I would not think any thing in the controller could cause this issue but I can not say that for sure.

The other thing that comes to mind is a bad connection causing it to arch which will cause voltage spike.

David

[Six_Shooter]

Have you verified this "runaway voltage" at the battery with a DMM?

If not, start there, verify what the actual vehicle voltage is, both at the battery, and the input to the MS.

It seems unlikely that actual vehicle is go that high, and that there is likely something happening in the MS itself.

If the vehicle voltage checks out look at the resistors R3 and R6, this is where the MS gets it's voltage reference from, this voltage divider. If R6 has poor connections than it's possible that TS would display very high voltage without actually being that high. Though the voltage at AD4 would likely be getting high enough to cause some damage, if my suspicion is correct.

[DaveEFI]

No chance you'd see 25v at the actual battery - unless the battery was near open circuit and the alternator faulty too. Highest I've seen with a faulty alternator turned hard on with a good battery is under 18v. 25v into a good battery would likely make it explode.

[Six_Shooter]

No chance you'd see 25v at the actual battery - unless the battery was near open circuit and the alternator faulty too. Highest I've seen with a faulty alternator turned hard on with a good battery is under 18v. 25v into a good battery would likely make it explode.

I agree, which is why I'm suggesting to verify actual voltage. ;)

Like you highest I've seen was 18 or so volts. Happened in my old Sunbird, when I was at school about 2.5 hours from home, in January when the highway home was backed up...

I turned EVERYTHING on, and as high as I could, including my fairly powerful aftermarket audio system just to get the voltage down to about 16V so that I wouldn't absolutely fry everything. lol That was a loud bright ride home. Man that stereo sounded awesome with teh extra voltage though. These were the days before fully regulated power supplies in amplifiers. lol

[trconn]

Thanks for the replies,
This is a recent problem. Things were working properly a couple of weeks ago. Voltage was normal according to previous data logs.
The alternator was completely disconnected for the test.
I cleaned the contacts when had the alternator checked.
Voltage at the battery does spike up to 18v. This must be getting to the MS.
I’ve looked at the board a couple of times verifying parts and orientation. I’ve also re-soldered most of the connections and gone through the assembly and troubleshooting tests.
A couple of things that may have some bearing on the problem
- Even with the jumper on D2 I can’t get a tach signal to the stimulator. Though the engine will (did) start & run just fine.
-Without the jumper, the engine will start momentarily then die – no tach signal, so no fuel
-The 3 LEDs on the MS do not light, never have.

[rickb794]

If something is pulling down the Vref (or the regulator is failing) the TS indicated voltage at the MS should rise, would it not?

[racingmini_mtl]

If something is pulling down the Vref (or the regulator is failing) the TS indicated voltage at the MS should rise, would it not?

Yes and that's what I suspect is the problem. Measuring the 5V supply would confirm and removing the MS2 would also confirm if the issue is on the MS2 or the main board.

Jean

[Six_Shooter]

If something is pulling down the Vref (or the regulator is failing) the TS indicated voltage at the MS should rise, would it not?

Yes and that's what I suspect is the problem. Measuring the 5V supply would confirm and removing the MS2 would also confirm if the issue is on the MS2 or the main board.

Jean

There's also the issue of the actual battery voltage going to 18V...

So this 18V at the battery is with no alternator or form of charging in the system? Does the DMM have good strong/fresh batteries?

[trconn]

The main board power supply reads as it should per the testing procedures.
Ignition on: 12.5v in 5v out.
Sounds like the MS2 board.
Is there a way to check/repair it or is it something that just needs to be replaced?

[jsmcortina]

Measure the voltage across the H1 jumper on the mainboard - it should read 1/6th of the supply voltage. Check that the MS2 is firmly seated and that the soldering on the underside of the mainboard is good on the DIP40 socket.

James

[jsmcortina]

Also, do the voltage checks on the DIP40 socket. If you are careful, you can do this with the MS2 in-place also. Be certain not to short adjacent pins.
http://www.msextra.com/doc/pdf/html/MS2 ... 4-195.html

James

[trconn]

Bummer!
While testing voltage at the power transistor I accidenaily shorted it out, U5 is now dead.
So I need to order another, should I go ahead and get another daughter card at the same time?
You know, its only money..

[trconn]

Received and installed new U5 power transistor. Checked with the stimulator. Strange…
Though it shows up as “on line” there is no tach. signal at anything less than about 13.6 volts. Is this normal? I still have the jumper on D2.
At the higher voltage things seem to operate as they should.
I’ve attached an .msl form the stimulator which shows the readings drop off when the voltage is below the threshold.
I haven’t tried to start the car with this yet, but it seems as though it will be a no start since there is no way I’m getting 14v while cranking.

[DaveEFI]

U5 is an IC 5v voltage regulator - not a transistor. You did replace it with an identical one? I'd also check the tantalum caps either side of it, if it had failed.

[trconn]

I ordered the U5 voltage regulator from DIYAUTOTUNE, so it is the correct one.
I'll order the caps today. I don't know if they are bad, but it can't hurt to have new ones.
Are there ANY other parts that might be involved? I'd like to just order them all at once rather than stringing this out over a long period of time.
I need the car running on Nov. 5th and really don't want to go back to the carbs.
Thanks for the help.
-TRConn
Looking at the page on DIY for ordering caps there are several different "kits" which one do I need?
MS2 v3.0. At the price, I'll get a few sets.

[rickb794]

I think it will run with out the caps for testing purposes?

[trconn]

I have replaced the voltage regulator and caps C-16 and C-17.
The regulator reads 5.1v at any input over 6v.
I removed the daughter card and got 5.1v at pins:
1 – 2, 19, 32
20 – 2, 19, 32
31 – 2, 19, 32
Voltage at H-1 is 2v with 12v input
Still no tach signal below 13.5v. When I turn it up above 13.5v everything works as it should even the LED's are working now!
As I recall (vaguely) the problems began when I removed the jumper from D-2 (24v zener diode, backwards (50-B-iv)). The instructions say to remove the jumper, but this resulted in a no start. I re-installed the jumper and things were never the same.
The questions remain: What happened and how do I fix it???
As always, thanks for your input.

-TR Conn

[trconn]

I'm still looking for answers.
I thought I had it fixed for a couple of days, but no.
The car is now running, but not well.
Current symptoms:
Start, warm or cold, after about a minute the engine runs very erratically, idle rises and falls (500 - 1500 rpm) then every time the engine surges, the voltage goes up a couple of volts until it pegs the meter in TS.
After a couple of minutes of this behavior it tends to smooth out and run OK. Though the voltage doesn't come back to normal.

[rickb794]

Where are you located? I'd like to run your box on a test bench.