Power failure while cruising

[9ewartc]

1968 BMW 1600-2, 2.0L BMW M10 engine, Jenvey 45 ITBs, preassembled DIY Autotune MS III with MS3X V3.57, MS3 release 1.2.4, MS relay board, TunerStudio MS v2.6.04, VR crank trigger for tach, VAG COPs, LC-1 wb. Megasquirt controls fuel and spark. This is my first MS install.



Car feels like it runs well. Took it to a local shop for fine tuning on their dyno with excellent results (ok, excellent results for a N.A. M10 anyway) - short video at the following link:

http://youtu.be/yr_LMgSI7Iw

Known issues that I am working to resolve:

• erratic CLT sensor readings (grounding issues?)
  erratic o2 readings (grounding issues?)
  o2 sensor reading lower the dyno operators tail sniffer
  intermittent complete power failure
  coils overheating affecting ignition due to heat from header (only an issue in heavy stop/go traffic - heat shield on the way)

The current tune was developed on the dyno when the o2 and CLT sensors were wildly inaccurate and the o2 sensor was known to be reading low (I'm learning as I go), but I have since improved the situation by moving the LC-1 sensor and heater grounds to the chassis. They were grounded at the MS relay board with all other sensors previously. CLT remains grounded at the relay board. I need to revisit the tune since things have changed.

The power failures are the prime concern right now. They don't seem to coincide with any particular event - no bumps or jolts, no hard acceleration, cornering or braking. They have all occurred during cruising. I can drive for many miles before it occurs. I think the longest drive has been 30 mins/30 miles before it first occurred. No power outages during the dyno tuning (3 hour session) or any time prior to it. It was only after the dyno session that I moved the LC grounds to the chassis, and that's about the only change I can recall that I made before the power failures started. I will be cruising anywhere between 50 and 80mph and suddenly it feels like I removed my foot from the accelerator pedal - gradual loss of engine RPMs until it dies. I coast and pull over, turn the ignition off, turn it on again and it fires up immediately like nothing happened.

I have captured datalogs when a power failure occurs, and the logs show voltage dropping as seen by MS. Battery appears to be charged and charging properly. Alternator is an reconditioned upgraded 85amp unit (factory is 45amp). I do not (typically) see any sync loss during these power failure events or at any other time.

A loose connection is the most obvious cause for power failure (still checking), but the fact that the car starts right up again after a power failure suggests that it could be something else.

• Am I really suffering a power failure or is the voltage drop seen by MS a symptom of something else?
  Is there anything else in my MSQ/logs that stands out as needing attention?

Thanks in advance,

Colin

[Matt Cramer]

Could it have fouled the spark plugs from running too rich?

[billr]

I would focus on finding out why the "battery voltage" logged by MS drops so suddenly and so low. Strap a voltmeter onto your dash where you can see it easily when the engine is dying. Read voltage between an MS ground pin and the "raw 12V" pin; let's start there.

[9ewartc]

Thanks for the responses.

Multimeter shows 13.8V across the battery terminals when loaded (blower motor, full/high beam, Hella driving lights), and 13.5V with no load. MS shows around 13.2V or 13.4V during the same tests. I would expect something above 14V at the battery terminals when running. Perhaps my new (recon) alternator (built-in VR) isn't performing as expected?

[billr]

I doubt the alternator is the problem, even if it crapped out completely the battery would provide sufficient voltage for far longer than the second or so that the voltage is going so low and the engine is dying. That's kind of assuming the alternator isn't failing such as to be a big short-circuit on the system, but if it were I think it wouldn't come back, something would burn out. I always figure 13.5-14.5V is normal for an automotive charging system.