I have a 2000 SE. When I start the vehicle the needle on the gauge sweeps and goes to about 12-14 volts for about 30 seconds to a minute then it drops down to the min. 8 volts reading and the check gauges indicator comes on. It will remain in that position until the vehicle is turned off. I've had the alternator checked and it shows to be charging a continuous 14 volts. I don't know if there's any connection to the current problem, but I have noticed that when I hear the fuel pump kick in I also hear a relay in the back seat fuse box click and the needle on the volt gauge drops at the same time. I've tried changing the fuel pump relay with no luck. I am wondering if the inital surge in voltage when the pump kicks in is what is causing the voltage problem that I am having with the gauge? I know that changing the pump is relatively simple, but I don't want to spend the money on something that might not need replacing. I currently have about 45 psi. at the injector rail. Has anyone encountered this or have a solution?

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LocoWBL

Your fuel pump won't be a factor, so don't sweat over it any more.

I understand you had the alternator tested, but was it on or off the car when it was? Do you have a voltmeter to test it yourself after it drops? How old is the battery?

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93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

It was tested twice at two different shops off the vehicle and I tested it on the vehicle with a volt meter. It shows 14 continuous volts. The battery is about three years old. Regarding the battery I should mention that a week ago the vehicle was out of service for a few days. I had an over heat issue and I ended up replacing the upper intake manifold. When I went to restart the vehicle I found that that battery was down enough to no want to turn over the motor. After charging the battery I was able to start the motor and have not had any further issue starting the motor, but this is when the gauge started acting up.

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LocoWBL

It tests 14v at the EXACT same time period the gauge shows 8v?

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

Correct. Please note that I edited my previous post, maybe the additional information could help.

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LocoWBL

Thanks for the clarification. Batteries can do funny stuff. I had an old battery in the SLEeper for about a year, it would start out at 14v, then once the car warmed up, it would drop to 10-12, and how far depended on the defrost, headlights, etc. I was charging 14 volts initially to make up the charge the battery was losing overnight, then it would drop down, as the cells were eroded to the point that they couldn't take a full charge.

Changing the battery solved the issue, but I initially suspected the alternator (until I did diagnostics on it, one of the nice functions on my kick-ass charger). I'd rule the battery out if I were you, before going any further in troubleshooting. I'd be tempted to simply piggyback with jumper cables for a quick test drive (leave the windows cracked for ventilation just in case, and wedge the battery into the footwell with something so it doesn't tip).

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

I tried hooking up the second battery with the same results on the meter. I drove the car on Saturday, Sunday and Monday It cranked fine, but the gauge would drop down to 8 volts with in a minute of running. Any way got in this morning to head back to work and it wouldn't crank. I'm wondering if I might have the same problem that you mentioned. I'm going to put in a fresh battery this afternoon.

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LocoWBL

The old battery tested bad. Replaced it with a fresh one. The fresh battery cranked the vehicle, but the volt meter problem continues to baffel me. I show continuious 14.3 volts with two different meters at the altenator and the battery but the gauge only shows 12.5 volts until it drops to 8 volts after the vehicle has run for about one minute.

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LocoWBL

Was the alternator 'tested' on the bench or on the car?

Is the new battery sealed and/or vented?

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

The alternator was first tested at a local auto parts store and then at a shop that rebuilds starters and alternators. They both said that it was charging correctly. I have also tested it on the vehicle with two different volt meters. They both show 14.3 volts at the alternator and at the battery.

The new battery is vented through the caps, but doesn't have the vents on the side for connecting the factory vent system.

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LocoWBL

You want the type vented on the sides to use the vent tubes. It will give off harmful gases into the passenger compartment.

I'm planning on changing it this weekend. I just thought I'd give it a try. The only thing I'm noticing is a slight odor when the windows are up althought I don't think it's the reason the gauge is acting up being that was occuring prior the the replacement of the battery.

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LocoWBL

Hey guy's I'm still trying to get to the bottom of the voltage issue. Anybody have any other ideas or something to try?

This may or may not be related to the voltage issue, but the security light is now coming on some of the time and when it is on the AC clutch will not engage.

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LocoWBL

Well I’m still trying to get to the bottom of this issue. I had the alternator rebuilt this week. They told me the only thing wrong with it was the brushes were almost worn out. I put it back on hoping that it might some how that might fix the problem, but no luck. I’m totally out of ideas. I hate the thought of taking it to the shop because I can only imagine what they would charge track down the problem.

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LocoWBL

How old is your accessory belt, and which tension mark is the tensioner aligned to?

Do all your other pulleys on the belt path spin freely? For those with 2k FSM's, is it possible there's a sense wire fault? I find that hard to believe considering the symptoms.

Next time it does this, pull over, and make sure the gauge is still reading low on the dash. Check for power at the battery AND the hot post on the back of the alternator. Post all 3 numbers.

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

maybe you stated this in some of your posts and i missed it, but if you just turn the key to run, does the voltmeter indicate about 12.6 (for a fully charged battery) and remain at that voltage no matter how long you leave the key in run (engine not running)?

edit: 96 FSM says key in run, engine not running, use portable volt meter and read battery voltage. then check that cluster gauge reads approx same. if not and other gauges work ok, then change out instrument cluster (easy for them to say).

edit NO. 2: NOTE, if instrument cluster volt meter reads same no matter how long key is in run and only drops to approx 8 volts after engine is running, this would seem to negate changing out instrument cluster (maybe).

if you are adventurous, you can rig a 2 wire cable from battery, thru window and connected to hand held voltmeter to once and for all verify while driving that instrument cluster gauge drops and battery/alternator does not (or does).

I was thinking the same thing, then you can compare in real time the differences or similarities between the two.

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1999 Bonneville SE with the heart of a 07 Grand Prix

I replaced the belt back in January when I overhauled the motor and transmission. I’ll get the other information you requested this evening when I get back to the house and post it tomorrow.
I’ve been trying to think of a way to test the gauge but haven’t found a good way to do that. I removed the instrument cluster and there was one master plug for all the different gauges and not knowing what pin feed the volt meter I reinstalled the cluster back in the dash. I tried to buy one from harofreak00 but he’d sold the only one he had that would work with my vehicle so I’ve got one coming from e-bay, but that will probably take a week or so to arrive . I hadn’t thought to see what it does with the key in the on position. I’ll try that also and post the results.

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LocoWBL

Here’s the reading I took.
12.85 volts @ the alternator with the key off. 12.58 volts @ the battery with the key off.
12.20 volts @ the alternator with the key on. 12.29 volts @ the battery with the key on. I’m attributing the voltage drop to the fact that that the head lights were coming on while I took this reading.
14.78 volts @ the alternator with the engine running. 14.42 volts @ the battery with the engine running. Both of these readings never changed prior to and after the voltage drop. The voltage on the instrument cluster was 12 to 13 prior to the drop to 8.
Regarding the belt tensioner as I’m standing in the front of the motor there are three marks on the fixed portion of the tensioner the first being on the the left closest to the firewall and the third being closest to the direction of the radiator. There is one mark on the spring portion of the tensioner that is in the middle second and third marks of the fixed portion. Sorry for the lack of a better description.
With the key in the on position the voltage on the instrument cluster is 12 to 13 volts and does not drop. It only drops after I first start the engine and it has been running for approximately 30 seconds. It’s like there is a heavy load on the system and the voltage drops.

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LocoWBL

it appears that your gauge cluster voltmeter, alternator and battery are ok. i cannot concoct a scenario otherwise. it seems nothing remains but to wire check/connector check from point-to-point from battery to instrument cluster voltmeter.

i don't have 2000 FSM but will be glad to offer point to point check of wiring from 96 FSM. maybe it will be close enough to establish main check points. will wait to see if other members can provide 2000 shematic.

if you have already ordered instrument cluster, change out the original although i don't see how it could be causing problem. i have learned that there is FM in electronic circuits. PM for definition of acronym FM if not known.

one last thought, would still suggest external wire from battery to hand held voltmeter to be absolutely sure battery voltage does not drop when IC voltmeter shows 8 V. however, if IC voltmeter shows 8 V with car not moving, and a handheld voltmeter shows battery voltage at 12-14, external wire check would not be necessary.