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A930Rocket's Avatar
 
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UPDATE: Why can I drop my engine faster than I can replace the alternator?

The car was dieing on me and I'm only getting about 11 volts at the battery, so I swap out alternators yesterday. Not my first time, but I had forgotten what a pain in the ass it was. Why can I drop the engine faster?

Anyway, I figure I'm good to go and take her for a spin. Get a mile from the house and it starts to sputter, then slowly die on me. She starts right back up and I bring her home.

Just to make sure everyone knows I'm having a problem, it starts to do a few small backfires, then a big one. Everyone looks at me like I'm the village idiot. Well, I felt like one.

I checked the fuel pump relays and they were cool, as was the fuse. Maybe swap out my MSD for the stock box to eliminate that. Next I'll check voltage at the battery (its new), then start looking at grounds and follow the pos lug off the alternator to see where it goes and check voltage off that. Anybody know where it goes to?

I hate electrical problems...

Last edited by A930Rocket; 12-28-2008 at 10:22 AM..
Old 12-27-2008, 12:09 PM
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I have had similar problems on different cars over the years. On one it was the ( green if replaced or the original brown pig tail version ) wire that goes to the distributer. The inside wire is hot and there is a ground wrapped around it and insulated also. A tiny wire to service both +&-. Very similar in design to the factory much larger spark plug wires. Also at the quick disconnect it can be grounding ( on either side) . Worst is to have to replace the wire from the disconnect to the MSD. Any of the before mentioned wire deterioration usually starts as a intermittent problem as you described. Initially the problem starts to occur in high humidity, rain, washing car etc, if this is the cause.

Last edited by voitureltd; 12-27-2008 at 12:55 PM..
Old 12-27-2008, 12:48 PM
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It started early last spring at VIR on the last day. It was a high speed miss. Couldn't find any thing wrong, but the battery was dieing and voltage was low. A new battery didn't fix it. Haven't driven it but a few times since for various reasons and it's gotten worse. Just got around to replacing the alternator.

Do you know where the pos lug off the alternator goes to?

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Originally Posted by voitureltd View Post
I have had similar problems on different cars over the years. On one it was the ( green if replaced or the original brown pig tail version ) wire that goes to the distributer. The inside wire is hot and there is a ground wrapped around it and insulated also. A tiny wire to service both +&-. Very similar in design to the factory much larger spark plug wires. Also at the quick disconnect it can be grounding ( on either side) . Worst is to have to replace the wire from the disconnect to the MSD. Any of the before mentioned wire deterioration usually starts as a intermittent problem as you described. Initially the problem starts to occur in high humidity, rain, washing car etc, if this is the cause.
Old 12-27-2008, 01:21 PM
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Jim I have my motor out and going on memory, that wire goes to the starter.

You talking this red one, right.
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Old 12-27-2008, 01:44 PM
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Yes, the two red ones. I kind of figured one or the other would lead to the front fuse box.

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Jim I have my motor out and going on memory, that wire goes to the starter.

You talking this red one, right.
Old 12-27-2008, 03:39 PM
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Don't you have those pretty colored wiring diagrams? I made copies of those from you and now I can't find them, as I was going to look up the diag for you. I am also thinking one of those red wires goes to the starter for it's 12V source, as I cannot believe they ran another 12V wire all the way to the Battery. I'll keep looking for the diag's.....
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Old 12-28-2008, 06:33 AM
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Quote:
Originally Posted by A930Rocket View Post
. . . so I swap out alternator yesterday. Not my first time, but I had forgotten what a pain in the ass it was. Why can I drop the engine faster? . . . the pos lug off the alternator to see where it goes and check voltage off that. Anybody know where it goes to?

I hate electrical problems...
Count your blessings - I have to remove the engine to change my 930's alternator.
The large red wire from the + terminal of the alternator goes to the starter motor lug, common to the + of the battery.
To check alternator output, check voltage on the battery, engine off. Should be near 12-12.5Vdc. Start engine, get RPM above 1500, check voltage on batt. Should be 13-13.5Vdc. If so, alternator is fine.
Not likely MSD. Have you removed the resistor in the rotor, replaced it with solid 12AWG solid copper wire?
Old 12-28-2008, 08:33 AM
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UPDATE

I jacked the car up just now and took a look at the starter leads. The nut had backed off slightly and the leads were slightly loose. Cleaned them up as well as the trans to body ground. Replaced all nuts with new jamb nuts. One hour max time working. I now I have 13.8 volts at the battery and cut off switch. Need to take it for a spin, but I'm sure I've fixed it...

Moral of the story: Check your wiring first before you spend the money and time!
Old 12-28-2008, 10:20 AM
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Hey Rocket...sorry to hear about your troubles and glad that you're fixed up, now!

Just out of curiousity, was/is the alternatory hard to remove with the engine in the car...was that part of your frustration? Or was it the electrical gremlins that gotcha? I've only had my alternator off during an engine rebuild, so I've never tried to pull it with the engine in the car. Just wondering what to expect when I finally walk that road!!! Also, my car is an '87...just curious about brand/model and source for new alternators.

Thanks,
Jeff
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Old 12-30-2008, 05:25 AM
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Thanks Chris. I have 12.1V at the battery, engine off and 13.8, engine running. I've not remved the resistor out of the rotor, but have never had a problem over the years. Got lucky over the years. I have just recently ground out two rotors to do the job though.

Quote:
To check alternator output, check voltage on the battery, engine off. Should be near 12-12.5Vdc. Start engine, get RPM above 1500, check voltage on batt. Should be 13-13.5Vdc. If so, alternator is fine.

Not likely MSD. Have you removed the resistor in the rotor, replaced it with solid 12AWG solid copper wire?
Old 12-30-2008, 06:14 AM
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Jeff,

It's hard to remove the alternator because of the engine shroud and carrier/crossmember. They do not allow the fan housing to be brought out as far they could if they were removed (and the engine out). All you can do is get it out far enough to angle it so that you can get your hands in there and with a combination of wrenches and sockets, remove the three nuts that hold the plastic and metal air deflector in back. This allows you to get to the three wires in back of the alternator. Once you get those off, you can pull the fan housing out, remove the other three nuts and pop out the alternator.

Re-assembly is the same: A PAIN IN THE ASS!

BTW. youwould be amazed at how many times it takes to re-install the fan on the alternator shaft. That darn key just pops out repeatedly. I finally rounded off the front edge of the key and fan key opening just a hair so that it would allow the fan to slip on. Now, instead of 37 tries it takes only 12.

I got mine rebuilt from V****x. They are a little cheaper, closer and I get it one day. If I had the money, I would have gone new.

Quote:
Originally Posted by sand_man View Post
Hey Rocket...sorry to hear about your troubles and glad that you're fixed up, now!

Just out of curiousity, was/is the alternatory hard to remove with the engine in the car...was that part of your frustration? Or was it the electrical gremlins that gotcha? I've only had my alternator off during an engine rebuild, so I've never tried to pull it with the engine in the car. Just wondering what to expect when I finally walk that road!!! Also, my car is an '87...just curious about brand/model and source for new alternators.

Thanks,
Jeff
Old 12-30-2008, 07:29 AM
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