Question about 1994 Cadillac DeVille

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Repeat Alternator problems

After replacing an alternator 7 months ago because I was getting dashboard warning errors of 'Over Voltage, Under Voltage, No Voltage, and Service Engine Soon…I three weeks ago I suddenly started getting the same errors which lead to my replacing the unit again.

With this 2nd new Reman unit, I found I was intermittently getting 'Battery No Charge' errors, coming on and off. So I put in the 3rd Reman and find I was getting this same error.

Base info: The battery is tested good with a load. The alternator tested good on two bench tests. Battery Grd cable to body frame are all removed and cleaned for good contacts.

Here's the situation: With a DVM connected to alt B+ post and Neg lead to frame, after starting engine I can see the alternator is putting out 14.5 or so volts.

Now here's the problem. - When I rev up the engine to 2000 rpm, the 14.5 v stays up for about 30 sec then you see the volts suddenly go down to 13.5 and continue to degrade down to 12.05 V or so! Let off the accelerator and voltage pops back to 14.5 V. When the voltage drops down below 13.5 V, this is when the warning 'Battery No Charge' comes on and off randomly!

On the Positive Side Voltage Drop test. Reading between the battery + term and the alternator + post, I have a reading of 0.18.

On the Negative Side Voltage Drop test. Reading between the – post on the battery and the alternator case, I have a reading of 0.13. This tells me my Grd cable and all connections are in acceptable condition and that I could have an alternator problem….

An alternator repairman says the problem is not the alternator. An auto mechanic and auto electrical specialist says it definitely is! I ordered a brand new Remy alternator (140 amp w/o heated W/S) and tried to install it today but found the case was about 4/32 wider than the normal alternators so it wouldn’t fit down into holding bracket. If I put the case into the front two spots, I found the back bottom of the case landed on top of the bottom bolt bushing. Normally it would have slipped down in front of it so the bolt could be screwed in! Now I've ordered another new Remy unit #91406 (20170104).

Now who has any idea about…..
1. What causes the voltage to erode after the engine is revved?
2. Is it reasonable I could put on two different Reman's and yet have the same 'Battery No Charge' problems?
3. What else in the engine electrical system might cause voltage to be lost when engine is revved?

My car is a 1994 Cad Deville 4.9L VIN B. It has a new serpentine belt and belt tension unit is working freely. It has new plugs, plug wires and a rebuilt distributor. All electric components (power windows, door locks, trunk release, fans, radio and etc) are working properly! The battery has never caused me a problem even at 20 below temps. It presently reads 12.5 with switch off after sitting all night!

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Hi again,

Any developments with the new alternator or the S jumper wire test?

Posted on Jun 24, 2008


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