Re: Newest Update

Spdloader wrote:
"Matt Ion" <soundy@xxxxxxxxxxxxxxx> wrote in message news:pUhrg.129222$IK3.68382@xxxxxxxxxxx

Spdloader wrote:

"Spdloader" <askforit@xxxxxxxxxxxxxxxxxxx> wrote in message news:Adkpg.4053$4c7.4030@xxxxxxxxxxxxxxxxxxxxxxxxxxx


Hi, I'm new to the group, but my daughter has a Honda now so I'll be lurking.
I didn't find anything on this exact problem in a search so:

Vehicle is a 1998 Civic DX 5spd.

Dead battery prompted a test of the alternator, which wasn't charging at all.
Replaced alternator, and externally charged battery overnight. The car started fine the next morning, and it worked fine for about 1/2 a day, charging between 13.8v and 14.2v, then the speedo quit working, then that evening the headlights were dim.

Next morning, battery was weak again, I charged the battery for a while, then started it, but now there is a no charge condition again, verified with a Fluke meter at the battery, but not at the alternator.

A brief check of the fuse block under the dash revealed a blown 10A fuse, Alternator / Speedo. Replaced it, had a charge at the battery, then blew the fuse when moving the vehicle in the driveway.

I suspect the vehicle speed sensor has a bad connection or is malfunctioning. Any other ideas before I dive back in tomorrow?

Thanks in advance!

Spdloader



Alternator taken off and tested, charged 20volts, 20amps on the bench, and voltage regulator bad.

New alternator installed, worked perfectly for 5 mins, then fuse blew, and I'm right back to square one.

Gonna go have a Mt. Dew now.

So something else is killing the voltage regulator(s - 4 of them now!), which then of course isn't regulating the output properly. Going by the schematic I found for the '97 Civic (http://media.honda.co.uk/car/owner/media/manuals/CivicManual/pdf/23-a96.pdf), that would most likely lead back to the ECU connection. The regulator actually controls the voltage across the field coil of the alternator, which of course affects the voltage produced by the rotor coils. From the diagram, it looks like the ECU also "injects" a voltage at the low side of the coil, which would allow it to alter the delta voltage in addition to the regulator (note: I have a good background in general electronics, but am not trained specifically in modern automotive charging systems, so some of this is just educated guessing).

A short in that ECU lead SHOULD'T affect the regulator directly, as there's a diode there that would block any reverse current flow if the ECU lead were to short to ground, but maybe the '98's alternator is different - without that diode, a short could potentially fry the regulator, allowing full voltage to flow through the field coil and cause the rotor coil output to spike. Or it might not even be affecting the regulator - just shorting that lead would have the same effect (then again, if it's testing overvoltage on the bench, the regulator probably is fried - damn).

So there you have it. Short of looking at a proper schematic of the '98, my best guess is still a problem in the ECU. The cooked regulators are a symptom, not the root of the problem.


I'd love to see a schematic of how the regulator itself is set up inside, it would help the diagnosis.


I wonder if there is something else in the circuit, i.e. sensors such as O2, or something that could be shorted somehow.

I don't think there'd be anything else specifically on that wire... the sensors would have their own connections to the ECU.

I think I'll let it rest over the weekend and do some fishing. I think I can do that right.

Heheh... like I said, try checking with a wrecker, see if you can get another ECU for cheap, and swap it in.
.

Relevant Pages

  • Re: Newest Update
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  • Re: Newest Update
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