MS board power backfeed

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SvenCS
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MS board power backfeed

Post by SvenCS »

The setup:
MS3 pro board wired to Bosch 55 pin connector adaptor board. Ignition driver circuit and baro MAP sensor added to 55 pin board.
Firmware version 1.3.3
Using Innovate LC-2 controller and sensor.
Capicitor installed between coil 12V and ground.
Diode installed in alternator excitor wire.

The Problem:
Runs fine, then every once in a while (when engine has been running awhile) engine sputters and stalls, voltage reading in TS jumps to 22 V. Unfortunately I have not been able to log this. I am sometimes able to open TS with key on but it opens slowly, if at all. Voltage reading is high. In the past to fix the problem I pull the fuses, relays, battery connection and after a bit of doing this the problem goes away, although I don’t know how exactly. The O2 sensor ususally needs to be recalibrated afterwards. With this latest occurrence I have not been able to fix the problem. It happened while car was idling in the driveway after a 15 minute tuning run.

After the problem the following symptoms occur: With key on and main relay removed, fuel pump runs continuously, stop and starting now and again. FP relay chatters. Getting voltage readings of of 5-7 v on both main relay pin 87 and fuel pump relay pin 87 (explains chattering). The main relay supplies voltage to the MS3 board. Is the power getting back fed from the MS board somehow?

I removed the following fuses from the circuit that the fuel pump relay feeds (one at a time to no avail.) then turned key on to see if the problem went away.

Fuel pump fuse (not the relay).
Coil fuse
Injector fuses
IAC valve fuse
Auxillary fan fuse

Also removed the fuses on the main relay circuit (with no affect)”

O2 power fuse
MS main power fuse.


Any thoughts are much appreciated,
Thanks,

Sven
2015-03-12_15.29.39.msl
BerlinMar12(1.3.3).msq
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

Make sure all outputs are connected to switched 12 volts and not constant 12 volt power.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

All outputs are driven from the Fuel Pump relay except the MS main input and the O2 sensor, which are on the same Main relay. It was suggested that the O2 sensor not be on the same relay as the fuel pump and other motorized stuff. Is it a bad idea to have it with the MS power?
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
S.Bretz
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Re: MS board power backfeed

Post by S.Bretz »

I had the same thing happen with a 3.0 pcd. It ended up being a bad diode. I found it because it was hot enouhh to burn my finger while poking around on the board. Im not sure how you would test for this on a pro unit.
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

That is an interesting possibility. Because the problem occurs only after the car has been running for 15-20 minutes, it could be that it take a component a while to heat up and fail. I was planning on running with my custom edu box lid off so I could point an infrared thermometer at the components. They are all very small on the pro board. Nothing visibly fried.

thanks,
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Update. I was finally able to catch the event on a log. Attached below. See it at time 5773 sec. The car had been idling about 20 minutes (I cut off the early section of the log). The AFR plunges to 7.5 and the batt V slowly creeps up to 20.7.

I also measured board component temps. No hot spots.

I am suspecting something wacky with the O2 controller?

Thanks,
2015-03-13_12_modified.msl
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

It looks like something is pulling VREF down. What's it wired to?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Matt, vref wired to:

MAP sensor (GM 3 Bar)
Baro sensor (DIYA)
Cam sensor (Cherry Electric GS100701)
TPS (Bosch)

would a short in one of the above sensors do this?

Does the fact that the O2 reading drops to 0V before the bat V start climbing tell us anything?

thanks,
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Matt,

How can you tell from the log that Vref drops? In the log, the sensors using the 5 volts from vref don't change when the "event" happens.
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

Yes, any sensor short could do this.

The tip off is that it shows battery voltage rising. This is being compared to VREF, but not powered by it. If battery voltage starts rising, this is often a sign VREF is pulled to ground.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Thanks Matt. I will explore this a bit by letting the event happen, then turn engine off, turn key back on and pull the sensors one at a time to see if the symptoms go away (the one where the FP relay is energized and the FP relay chatters). I may have a couple of spare sensors I could also try.

The fact that the event occurs when warm may help point to a sensor and not a wiring/connector problem.
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Could the Cam and Crank signals have any connection to this problem? Or is the below described conflict unrelated?

BMW VR sensor on 60-2 wheel.
Cam sensor picking up single tooth on cam sprocket.
CrankCamWiring.pdf
Attached is a composite log showing the cam signal showing up at each crank revolution. It should show up at every second crank revolution. Compare this to a screen shot of an oscilloscope of both signals.
2015-03-23_Composite.csv
Cam+Crank Signal.JPG
The o-scope reading looks correct. Why is the composite log reading like it does? There is also the occasional double cam signal per rev.

Regular log and cam only o-scope reading in next post. Same MSQ as in first post above.

Thanks,
Sven
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

The oscilloscope reading of the cam seems a bit noisy. Would it help to use the noise filtering function for the second trigger? A filter time of twice the time between which events?
Cam only signal.JPG
Log of engine idling while the above o-scope and composite logs were taken.
2015-03-23_Idle.msl
One more observation. The Lost sync reason 2 shows continuous in the log. There is no sync loss count however. Engine usually runs fine.
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

SvenCS wrote:Could the Cam and Crank signals have any connection to this problem? Or is the below described conflict unrelated?
Only if they're powered off VREF.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

The cam hall sensor is powered by Vref. If this is unrelated I can repost the other issue in a separate thread.
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

Ok, you can try running with the cam sensor unplugged and see if this stops the problem.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Yes, I will try that.

Do you know why the cam signal shows up at every crank revolution in the composite log, when the o-scope shows it at every other rev (as expected)?

thanks,
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Problem is proving elusive.

Update. In my trouble shooting efforts, when the problem occurs, I have tried pulling all the sensors (and even cutting the BARO sensor wires to the board) and it still shows itself with the key on - continuous running of the pump and chattering of the fuel pump relay.

The behavior of the problem has changed a bit (which may help diagnosis). Attached is the latest log showing the car running with the voltage going from normal to 22 volts and back a few times. This is new behavior. Before, when it did this, it would stay in the high voltage stage until things cooled down 30 minutes + usually. The items that have changed since then are below. After these changes I was able the run the car for 3-4 hours of driving before this version of the problem surfaced.

Tightened a slightly loose battery wire to alternator.
Replaced battery.
Replaced on board BARO sensor.
Replaced O2 sensor with AEM unit.
Installed 1k ohm resistor on Hall sensor (vref to output wire).

Is there anything I can test on the circuit board (MS3 pro module)? A bad circuit board voltage regulator? I am running out of ideas (except to buy a replacement board and transfer all the wires)

It seems to me that if the problem is with the vref shorting and causing the board to compensate by increasing the supply voltage then this would immediately go away when all of the vref using sensors are disconnected from the system. Not so. That is why I am wondering if there is something on the board that could cause this.

Thanks,
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
Matt Cramer
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Re: MS board power backfeed

Post by Matt Cramer »

Can you hook up a volt meter to the MS3-Pro Module's onboard 5V plane? A good place to read it is the right side of L2. It is separated from the VREF output, which is designed to track the internal 5V circuit.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
SvenCS
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Re: MS board power backfeed

Post by SvenCS »

Thanks Matt, yes, I can do that. I will try this weekend. I assume you want me to measure this when the problem is occurring so I will probably need to run the car awhile. It looks like the right side of L2 is directly above the letter M of the board label along the bottom.

This reminded me, that early in the install (last year) one of the small fuses blew because of of short that occurred in the engine bay. Perhaps that could have damaged something else?
1972 BMW 3.0 CS, v3.0 board, MS3 + MS3X, external MAP, VR-sensor, 60-2 crank, CAM gear tooth sensor, wasted spark, sequential
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