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Have a sudden bizzaro electrical problem which appeared last night.

When accelerator pedal is pushed away from rest slightly, all lights/access are ok, but oil light stays on when headlights are on. Temp gauges fluctuates tick-tock or wildly back and forth.

When accelerator pedal is released completely, power to all lights cuts (brakes/headlights/turns/accessories) and engine will eventually sputter and die.

Problem is suspected to be faulty ground/wire short or blown relay. I tried tracing accel linkage last night, saw no obvious wire interference/wear or shorts, only switches id'd where accel switch over pedal, throttle switches. I pulled the radio fuse just remove that as a potential, tried disconn the throttle sensor switchs, no change.

The issue began last night after hitting the horn button, which I'm guessing may never have been wired properly - I disconnected that too.

All fuses are intact and operational. Battery is fine, as it's charging/starting. No alternator squeal.

Is this a voltage regulator failure?

Has anyone run into this situation?

I would have done more creeping around in the dark last night, but I just had surgery, and am a few hundred miles from home - don't have full test kit, etc.

Any tips appreciated or it's going to a local shop (I'd rather diag/fix myself, within means).

Michael

Until an electrical guru answers, the famous tip is to make darn sure all grounds, brown wires and braided straps from negative battery and block to firewall are clean and tight.

After that, close fuse inspection, relay checks. Air Fuel Meter plugged in tight. Obvious, easy stuff first, maybe throttle linkage related,...before $$$ tools, calling 911.

Make sure you have a sturdy ground strap from the engine block to the body. Mine is in the area of the valve cover, at the rear passenger side of the engine bay.

Feeling much better and planning to dive into fixing this.

Does anyone know what the function is of the electrical switch is on the accelerator pedal? The one that is in closed position when the pedal is not depressed? I suspect that circuit is part of the trouble.

Other issues are probably ground and some wire fraying/corrosion after all these years.

Thanks for the tips - will post what the resolution is.

The answer is sort of opposite of what you're asking.

I'll venture to say that the ages have introduced electrical problems that can take time and be frustratingly troublesome to overcome but they can be with methodical troubleshooting. You need an electrical diagram of the car, and an understanding of where things are located on the car relative to the electrical diagram.

On a side note I once had a condition similar to what you originally posted that revealed itself as a shorted cell in the battery. All the gauges would go crazy, tach pegged, as the engine was cranking before ignition. A new battery solved that one but it was creepy weird.

The throttle-valve switch is dual-functioned. Closed at WOT enriches the mixture so when you nail the pedal, the transition from part-load to full-load is smoother. The closed at idle switch basically tells the ECU the engine is running and is operating in idle mode. When you are at part-load and decelerate (coasting) above a predetermined RPM the open position of the switch tells the ECU to cut off fuel to the injectors until you either accelerate or fall below the predetermined RPM level where the ECU then sends fuel to the injectors. The exact positioning of the idle switch to open immediately after the throttle is opened can affect drivability from idle to off-idle upon acceleration. It can take trial and error to get it just right.

BTW, these are my own words of interpretation of the Bosch L-Jetronic Technical Instruction manual I frequently paraphrase and encourage others to seek and digest.

ISBN 1-85-226008-4

Understood. I've been trying to diag this while 400 miles from home, with little daylight time or tools, but am back home for the weekend and will tackle again tomorrow.

I replaced the voltage reg, which seems to have helped just a little, but there's clearly something awry, next on my list are battery and ground cable, which I discovered has nasty corrosion from when the car sat beachside at the shop.

Disregard the comment abou the accelerator switch - I was looking under the dash in the dark with a flashlight and pointing at the wrong thing whilst crouched under the dash.

Like you say, I'm thinking the issue may well be battery, which I was getting ready to replace anyway. All realys so far look good, car starts and runs, just drove it back from San Jose to Los Angeles, just can't trust headlight/signals at night with foot off the accel - what a great prank for murphy to pull outta the bag!

I'll report tomorrow - got my volt/ammeter and stuff, no schematic, but I can wing it tracing between dash/fuse/relays and battery if need be - thank goodness it's not a 2008 M3 where you need a PhD and phone-home to Mama BMW AG. ;^)

boxeswithknobs wrote: next on my list are battery and ground cable, which I discovered has nasty corrosion from when the car sat beachside at the shop.

These are critical, and can't be clean enough. Inspect the wires as they enter the battery clamp, remove the wires from the clamp, freshen the wires as they enter the clamp, or replace the clamp. These are all crucial areas of potential electrical resistance. You don't want any.

I would hazard to suggest you may have other electrical issues from the car sitting in an extremely corrosive environment.

The two positive leads that connect with the main + battery cable can cause grief. Snip the end connectors off both cables and remake new crimp connectors. Solder is a plus !

Oooooh-kay!!!

Now that I'm home in LA, checked voltage at cig lighter - 8-11v, no wonder!

Mad scramble to try to get parts before everybody jets for the holiday, annnnnnddd....

1) Ordered a new ground cable - Mesa Performance had one, also requested a new ignition switch (electrical) - only the cable arrived this Sat AM, so I hopped down to Costa Mesa to pick up

2) Stopped by Radio Shack, bought new crimp spades

3) Picked up a new battery at Pep Boys with felt separators, fuses, and contact protectant

Swapped out the old bat, plugged in a new voltage regulator, changed ground cable, changed cable ends, sprayed contact cleaner on all ends, scraped the ground mount on the engine clean, remounted everything, hooked up battery, and....

Clear start, headlights, access all look good, full load electric all looking good. I think we're done. Tenative culprit is a bad battery, prob a cell issue??

Still going to get an ignition elec switch to keep in glovebox, otherwise, she's feeling 100% better, and should allow me to drive at night again, so I can head up to Fairfax Monday.

Have to give the engineers credit - that was an AMAZINGLY survivable failure - engine still ran, batt charged seemingly ok, just poor heavy load conditions.

One for the files.