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'87 Alternator help

 
Old 06-07-2019, 04:12 PM
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Vets87Vette
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Default '87 Alternator help

I recently had my alternator replaced as my old one was going bad. Everything ran smooth and pointed to the problem being fixed until the engine got to 192⁰. At that time the engine would stall if coming to a stop in gear unless I shifted to neutral or park. I read on other postings this could be a ground issue, confirmed with my mechanic he agrees as everything else checked out. Well I went to go look for the grounds and noticed a bolt was left off that connects to the engine block, I figured this was a support piece (so of course I want it fixed properly) but is it possible that it is a ground point for the alternator as well? Picture shows what I'm talking about.
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Old 06-08-2019, 09:35 AM
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Capt Mike
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That particular "Rear Brace" will provide a direct ground to the engine Block. I would remove it and clean the contact surface at both ends and the block mating surface.

True,, Electronic Modules to include alternator regulators required Clean and Solid grounding. Especially the high Currents in these alternators,, a capacity of 100 + amps in this return grounds path.modern vehicles.

If your motor is Stalling Out at an idle,,, then your alternator is most likely pushing a very large current into the Battery. So either the Battery is at a very low Voltage (requires charging), The Battery is Sulfated, or some other damage, or the new alternator is defective. Measure the battery voltage and have it load tested and a SLOW charge after if the battery is good...

I would first measure the battery voltage, preferably after 24 hours so the battery is at rest. A lead Acid battery should be 12.8 fully charged. If you have a AGM battery, consult the maker, but it will be close to 12.8 volts. If the battery is considerably lower than 12.8 volts, your battery is seemingly Shot,,, get it tested, a local part store.

Remove the "Field" wire, green / white, from the rear of the alternator. This will disable the Field circuit and the alternator will no longer charge.

If the alternator is still charging, the alternator is defective. So, if the alternator at this point still stalls the engine at idle, or is charging over 14.4 volts (lead acid battery AGM's are less) Then your new alternator is defective.

And, I have seen several alternators recently that "Out of the Box' had defective shaft bearings. Your can remove the Serp belt and if the alternator spins rough. slow, or it takes effort to turn the pulley, one or both of the rotor shaft bearing ares shot.

Good Luck.

M..
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Old 06-08-2019, 09:43 AM
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Vets87Vette
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Capt. Mike, thanks for all the info, as far as alternator is concerned everything checks out there, spins freely no issues or roughness to it, voltage coming out is right where it should be, under load and not, battery is 1yr old and with the issues from my old alternator battery is my next check now that I have that grounding bolt back in if i continue to see problems. I just got it home from the shop so I'm about to clean all the old bolts on the block and back of the alternator as you suggest, and the block itself.
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Old 06-08-2019, 01:47 PM
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Vets87Vette,

Good, but on the way home it would be a good starting point to have a Free battery load test completed at an auto parts store.

Another common problem with changing circuit that does not "Usually" result in over-charging is a internally corroded wire. Eventually the wire strands inside the wire will fail and break in half, this creates a Voltage drop when energized. Drives electronics crazy.

But the battery, alternator and starter require heaver wires, for heavier loads. Auto makers often Skimp on wire size, quality, and the actual connector and the ends of these wires. And the small hot engine bay damages the wiring.

A manual test you can do it to drive your car, still with this alternator issue, for at least 15 minutes, not to long.

When you get home turn it off and "Feel" the wires on the battery, & alternator ( bracket ground) ,, Both the positive and ground on the battery. . Start at a connection point and feel the entire wire. What your looking for a Hot Spot which can also have a Bump or wire size thickening. This will usually occur where the engine bay is the hottest, near any exhaust. Check the fuseable links by the battery.

Some Autos have the battery ground negative wire secured to the engine block. This is the preferred connection place. And some autos have the battery ground wire connected to the chassis. In both cases there must be a ground wire from the engine block to the chassis . Be certain this wire is in very good condition.

In my C4 Convert, I've replaced battery cables, a fuseable link, the connector with Pig Tails for the Fuel Pump Relays, and countless connectors and burnt wires over the last 2+ decades. The Fuel Pump Relays are unfortunately are both located next to master cylinder right over the exhaust manifold, where it gets scorching HOT The plastic Insulation on the wiring was melted that exposed the now bare wires, which then the strands started breaking one by one. Once the plastic starts to fail, the rest happens rapidly.

Again,,, good luck..

Michael..
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Old 06-10-2019, 01:19 AM
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Hot Rod Roy
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Did your "mechanic" forget to install that bolt? Talk to his supervisor! You don't need to put up with such shoddy work!! Never again!

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Old 06-10-2019, 06:26 AM
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Couple things I found once getting the car back a 2nd time. The cross bar that connects the back of the alternator to the engine block, was apparently powder coated by a previous owner, to include where the bolts connected. I stripped the powder coating at the connection points and reinstalled then went for a drive and got the car up to 200⁰. Which was difficult in 75⁰ and rain lol but I got it there. Went through every gear and watched and the volts never dipped below 12.3, and while actually driving forward it held at 13.8, reverse at 13. When I got home I found I had a vacuum line split in 1/2. The one that runs between the FPR and distributor cap. Got a connector to bridge the gap but haven't driven it yet but if rain good with the vacuum leak I'm guessing itll run good with it fixed.
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