ECU Failure

[dalebwilson]

Last week I was driving my normally reliable 93L to lunch and the battery charge light came on. I immediately thought I would drive to the nearest auto parts and have the alternator tested. After driving around 3 miles, the engine idle dropped significantly and sounded different. The windshield wipers came on and started going back and forth much faster than high speed and the car quit in the middle of the road. I have AAA and they towed me to Oreilley auto parts. I began troubleshooting and found the center 40A main fuse blown and several others on the inside fuse panel. After looking at the ICM, distributer, coil and testing with a multi meter, I concluded I was not getting a SPOUT signal from the ECU to the ICM. Sure enough, I replaced the ECU and all fuses and the engine cranked right up. I immediately checked the alternator output voltage at the battery and it was 18 volts and should have been in the 13.8-14.2 range. Of course the alternator failed the testing at Oreilleys and I purchased a new one. My question is this. Is there no protection for high voltage on the electronics and ECU's on these cars?

[jason_]

I always thought, on cars that are able to continue running with out a battery, is a no no, because if the regulator isn't a perfect, or flukes, when the alternator is turning there's no battery to take the extra juice, and the system smokes.

Not sure if that was your case, but food for thought.

Sent from my s-off'ed m7 with cm11!

[bhearts]

Current is the result of resistance though. Unless your electrical system is showing demands for more power (current), the alternator will not provide it. The battery is designed to flatten out the spikes of the alternator since it's output is pulsed dc.

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[mikemounlio]

Not sure on the festiva but i had an alt fail on my audi on thanksgiving day on my way home. I drove it 80 miles before i was able to make it to a walmart. It died in the lot (100% died). I threw a new battery in it made it the last 20 miles home. Changed the alt out and boom good as new. I didnt have any fuse or anything blow tho.

The old test of take the negative battery cable off to test the alt has been around for ages. I would think if the system didnt have a regulator of some kind that test would not be around still.

Check over the system on your car. Has it been modified? If so look at the wiring and see if its just working or done right. I would think you have a deeper issue then just a bad alt.

[bravekozak]

The ECU is protected by it's own fusible link on it's own circuit. Did someone accidentally wire power backwards into the ECU from a sensor wire?

[dalebwilson]

I did a B6-ME swap on this car a year ago and it has run perfect since. The wiring is unmolested from the factory other than moving the battery to the passenger side and moving the VAF to the drivers side. All work done by me and correctly.

[Flyin4stroke]

Alternators regulator broke and sent full voltage to the fuses. Fuses are the only protection. That's why it's important to always use the right fuse because it will blow before your electronics.

[dalebwilson]

Agreed. At idle the alternator was producing 18 volts. I can only imagine what it was at 3000 RPM. The battery was noticeably hot before the engine failure occurred. I am currently confirming the correct fuses on the inside fuse box. The engine bay fuse links have been replaced with standard PAL fuses with 30/40/30 amperages.


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[TominMO]

If you have a volt gauge and see this happen (18 volts), turn on the radio, and heater or A/C to bleed off same of the voltage. When my old Subaru's voltage regulator went out, the gauge went to 18ish. Turning on all the accessories brought it down to 13 or 14.

[Flyin4stroke]

Horror stories.

[dalebwilson]

Thanks Tom. That's good advice in the event this happens again.


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[ricko1966]

A bad regulator can indeed allow an alternator to produce way more voltage than many components will handle.The unfortunate thing for you is high voltage doesn't kill fuses high amperage does.Thats one of the reasons manufacturers switched to 12v from 6v systems work on an old 6v system the wiring is much heavier gauge.It is ohms law and basically if you change any of the factors in it all of them change proportionally,24 volts with the same load will draw half as many amps.It has been rumored for years that manufacturers are going to go to 48 volt systems to lighten the cars.

[ryanprins13]

Yes, i was going to mention that. You can have 5000 volts go through that fuse and it wont blow, its only amerage or draw that blows the fuse. You can buy a backup thing to regulate your voltage if you like it runs a wire from the positive terminal to a computer/box and then back to ground. Anything over 15 or 16 volts it sends to ground. Its handy insurance if you boost vehicles a lot or your worried about this happening.


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