Choreo

This is a clarification of a problem I am experiencing from another posted thread.

I should have paid more attention to how my voltage gauges behaved in the past, but now that I am having issues, I do not know what is correct?

(1) Do the Analog gauge and the DIC Voltage readout use the same sensor/sender? The reason I ask is because at times they do not agree exactly or maybe the digital info is just not updating as fast?

(2) What should my voltage gauge read?

(3) Should it be the same under ALL conditions (idle, WOT, etc.)?

I have a 3 year old Red Top Optima which I took out and put on the bench at AutoZone and they tested it for an hour and the result was "Battery OK". AutoZone then tested my Alternator with a tester and it showed "Diodes OK", "Regulator Low Output".

Next I took the car to the Dealership and they could see where the voltage was varying from about 12 to 14 volts on their tester and also decided it was a bad alternator. So, yesterday they installed a new GM (Made in France) alternator. A lot of my idling vibration issue has improved, but looks like it may be slowly coming back.

I drove for about an hour last night around town and noticed that the voltage on the dash would vary between 11.8 and 13.4. If I stayed on the highway at 60MPH it seemed to stay at 13.2-13.3 volts, but around town it would occasionally dip down to 12.2 (once to 11.8). Is this normal?

If not, what could it be? I came home last night and re-torqued everything the Dealer worked on (I watched them do the whole swap) and they did not use a torque wrench of course. The only thing I found was the main power bolt on the harness (where it attached to the back of the alternator) was showing a torque of about 7 ft-lbs, so I re-torqued it to the correct 37 ft-lbs and took the car for another 30-minute drive, but the voltage is still going up and down.

Any ideas would be greatly appreciated. This problem became noticeable a little over a month ago.

Todd157k

Since you got a new alt., it should not vary that much. That is the duty of the regulator. If the voltage is jumping around like that, I would check the main ground on the back of the passenger side head. You can get to it from under the car. Take it off and clean it, reassemble and check.
If that doesn't do it, then I would guess something is causing the voltage drop by taking a bit of current. Things to look for would be: loose connections at the battery, started, or alt., Also, look for burned wire (large gauge, not the little ones) where it travels along the motor.

check the book for actual specifications on voltages but usually 12.7 with the car off, 13.4-14.5 (or so) with the car running. It should never vary with RPM

Choreo

Also wonder if the battery may not be bad even though it tested good?

Todd157k

A bad battery will not vary the voltage as you described. It will either be a low voltage, or not hold a charge. A loose cable on the battery will vary the voltage.

Choreo

Hmmm... well I did double-check the terminals and they are torqued to 11 ft-lbs.

Something is definitely not right though. Just drove it again for about an hour and it held 13.5 on the highway steady, but as soon as it gets to a red light it drops to somewhere in the 12's today.

BuffaloBillHisself

I have to observe that the correct method of checking voltage is with a digital multi meter.

Connect anywhere in the car and monitor voltage while driving.

THEN do the same thing at the battery, again while driving.

A good mechanical connection is not necessarily a good electrical connection. Just because a connection is tight doesn't mean it's a good one. Clean the contacts. Clean the battery cables and their respective connections.

I agree with one of the other posters that your voltage should not be fluctuating as much as it is BUT it will go down when the car is not running.

If you have less than 12.8 volts AT the battery when you've JUST shut the car off (after driving for a while) then you have a battery issue.

hth,

Jim

mcgilles

definitely should not be that low. the target number while the engine is running is 14.4V. mine runs anywhere from 14-14.6 usually under load, and doesn't drop below 14 even at idle with a stock alternator and UDP. you might want to consider the big 3 upgrade (details in the car audio section) larger wire could help with charging issues and the procedure will have you cleaning up contacts. sounds like something is loose or corroded to me. fortunately that's usually a cheap thing to fix, but a pain to do depending on what you need to clean up.

Choreo

Well I just took the car to the local parts shop and had them run a charging system check again (since installing the new alternator yesterday). Once again the analyzer showed "Regulator Low Output"!

The guy said that does not mean there is necessarily anything wrong with the "regulator" - he also said it could be a bad ground.

So I guess I will be spending tomorrow searching for all the grounding locations!

Slick Rick

Your voltage is fine. It is normal for your voltage to drop any where from 11.8 to 12.2 reasons are brake lights coming on a/c on, ac motor cycling on and off air pump cycling on and off. Normal driving should be around 13.5 to 14.0 with ac on anything over 14.4 to 14.5 you are getting close to overcharging. Also in warmer weather 90 plus your voltage wont read as high as battery dosnt need as much to stay charged. Cooler weather it will read a little higher as the battery needs more to stay charged. Its not your alternator check the cable on your starter and make sure it is tight..............

Choreo

Could this be part of the problem?...

This is what my Battery Connection Cables look like. I wonder if part of the rubber boot is interfering with the metal to metal connection where it is flattened out? Is this what they are supposed to look like? As far as I can tell the metal that is covered up by the boot is flat and there is nothing to tuck the rubber behind? This obviously is getting wedged when torqued down.

dgrant3830

I've read in here several times where some are having similar issues. Some are finding bad crimps on the battery cables themselves and others are finding crimp connections on the starter wire. The ground connection right adjacent to the battery between the fuse box and battery has also been an issue for voltage related problems. Be aware that the PCM controls the charge rate. Oh, I remember seeing a post also that the alternator connection itself had burned wire insulation around it. Please note that any insulation that appears to be heated/burned, means a bad connection. I also suggest that you PM Bill Curleee as he's got a lot more information available.

corvettebob1

Actually the current path is through the bolt to the other side of cable end.
Remove the bolt and clean the cable end with baking soda and shine it up with a wire brush then do the same with the bolt and reinstall.
This will at least remove this from the equation.

bestvettever

Hi, yes that situation is a marginal situation. The bolt does conduct the current, but the cable is designed to bite into the terminal and make a very tight secure dirt free connection. If you can't tuck the plastic back properly, slice that intruding portion off, and for sure the connection will be improved.
Good Luck

Choreo

About to run out of ideas here?

The RevXtreme looks like a great solution for a beefed up alternator, but I am still under warranty and my original alternator never gave me any adverse idle symptoms for over 7 years - so I am guessing my immediate problem lies elsewhere.

(1) I have had the 3 year Old Red Top Optima checked on the bench and it shows to be OK. (still have my doubts since I never had a battery last more than 3 years)

(2) The Dealership replaced the Alternator with a New GM Alternator last Friday

(3) Last night I did a major cleaning of of the battery terminals, cable connectors, Ground 104, Ground 101, coated everything with dielectric grease before reassembly. All the grounds looked like new to begin with and the nuts came off easily - no corrosion). Also trimmed off a small amount of battery terminals boots where they were interfering (as shown in pics).

After reading one of Bill Curlee's posts, I checked the Voltage at the Battery, the Alternator and the Main fuse box with the engine off and ALL read exactly the same - 12.63 Volts with the engine off.

So what is next?

It is actually working worse today than before I performed step (3)? Idle keeps dropping to 400 RPM and car starts shaking when I come to a stop. If let up on the brake pedal and just let the car roll a few inches, the RPM picks up to 500 RPM and the shaking stops. Voltage range on the DIC today shows everywhere from 12.1 - 13.1 at idle and 13.1 - 13.6 at 45 MPH.

Slick Rick

Get a volt meter. With car running dont even look at your dic and and check volts at battery posts should be anywhere from 14.8 to 15.5 if it is there is nothing wrong with your alternator. If you have a 3 yr old red top Id junk it and pick up a new one. I run the duralast golds in all my cars. Reasons are theres autozones everywhere, you cant beat the warranty nad beleive it or not it is actually the same battery as the sears diehard. You being in Texas Im gonna assume you run your A/C often. Takes alot of juice to run one,. Rick

Choreo

No codes or warning lights.

What should the minimum RPM be on a stock set-up? What controls this - the PCM?

BlackZ06

I'd be suspicious of the battery.

Do you have access to another battery .... borrow/steal one from another of your vehicles or a neighbor or buddies vehicle ??? You just want something that allows you to start and run the Corvette for a few minutes ???

Yes, the PCM controls your idle. The PCM controls many functions, including managing the alternator, so voltage problems from a bad battery could affect a lot of systems in the car.

Choreo

Good suggestion. I was thinking of trying that this afternoon if I can find a replacement - worth a try.

Bill Curlee

There are a few more charging system electrical connections that you have NOT inspected and checked yet plus,, there are a few things mis-stated in this post.

First: The Ground connection on the back of the drivers side head is the ground for the Coils and the Ignition Relay #42. Its an important ground point that is often overlooked but should not effect your issue.

Next: Normal voltage readings for any C5 will be ( 13-15 VDC) The actual voltage that you will see at different charging points in the charging system will vary. The voltage observed on the meter in the gage cluster will/could be around .5 volts lower than the actual battery voltage. To obtain an ACCURATE charging system voltage you will need to measure the voltage AT THE BATTERY TERMINALS!

Here is how your alternator operates:

Charging System Description and Operation
Generator
The Valeo generator is electrically similar to earlier models. The generator features the following major components:

The delta stator
The rectifier bridge
The rotor with slip rings and brushes
A conventional pulley
The regulator
The pulley and the fan cool the slip ring and the frame.

The generator features permanently lubricated bearings. Service should only include tightening of mount components. Otherwise, replace the generator as a complete unit.

Regulator
The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

Radio noise control
Obtain the correct average current needed for proper system voltage control
At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Circuit Description
The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through a fuse link that is connected to the starter.. This voltage is used by the regulator as the reference for system voltage control.

Charging System Indicator(s)
CHARGE SYSTEM FAULT
The IPC illuminates the CHARGE SYSTEM FAULT indicator in the message center when the following occurs:

The PCM detects that there is a problem with the electrical charging system. The IPC receives a class 2 message from the PCM.
If the tachometer is less than 500 RPM and the power mode state is in the crank mode then this message will not be displayed. Instead the CHECK GAGES indicator will illuminate.
HIGH VOLTAGE
The IPC illuminates the HIGH VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is greater than 15.75 V for more than 5 seconds.

LOW VOLTAGE
The IPC illuminates the LOW VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is less than 10 V for more than 5 seconds.

Here are the torque specs that you need for the charging system components:

Fastener Tightening Specifications
Application
Specification

Metric
English

Battery Hold Down Retainer Bolt
18 N·m
13 lb ft

Battery Tray Bolt
12 N·m
106 lb in

Engine Harness Cable Nut
13 N·m
10 lb ft

Generator Bolt
50 N·m
37 lb ft

Generator Bracket Bolt
50 N·m
37 lb ft

Generator Shaft Nut
75 N·m
55 lb ft

Ground Strap Bolt
32 N·m
24 lb ft

Ground Strap Nut
8 N·m
71 lb in

Instrument Panel (IP) Wiring Harness Junction Block Nut
10 N·m
89 lb in

Negative Battery Cable to Battery Bolt
15 N·m
11 lb ft

Negative Battery Cable Ground Nut
8 N·m
71 lb in

Negative Battery Cable Terminal Bolt
8 N·m
71 lb in

Positive Battery Cable Bolt
15 N·m
11 lb ft

Positive Battery Cable Nut (at solenoid)
10 N·m
89 lb in

Positive Battery Cable Nut (at fuse/relay center)
8 N·m
71 lb in

Positive Battery Cable to Starter Motor Stud Nut
15 N·m
11 lb ft

S Terminal Nut
4 N·m
35 lb in

Starter Motor Bolt
50 N·m
37 lb ft

You need to check/inspect & clean and the following wiring connections:

Engine ground G-106. Engine block above the starter between cyl 6 & 8.
Chassis ground G-104/104

Starter: The alternator (actually called the generator) charges through the STARTER (actually the solenoid connections) CHECK the connections at the solenoid. You will need to remove the connections, clean them and reconnect them. There are fusible links between the wires at the starter solenoid. Make sure that there in good condition.

The battery terminals should NOT have any plastic between the battery terminal connection and cable terminal connection. There have been cases where the crimped battery cable terminal end to the actual wire corroded or was burnt and loose. CHECK THAT AREA! The correct battery to battery cable connection used the cable terminal & the bolt for the correct connection. The proper battery cable to battery terminal torque for 97-03 C5s is 11 ft/lbs.

If you DISCONNECT the battery and use an OHM Meter and read between the POS battery cable to the field terminal on the BACK of the alternator,,,you should read very close to ZERO ohms. The more resistance you read, the more voltage drop you will have between the alternator and the battery.

If you use a volt meter and read the voltage at the POS battery terminal to ground & the alternator field terminal to ground,,,the voltage should be the same (or very close to it).

Read the voltage drop between the battery POS terminal (positive meter lead on the POS battery terminal) and the alternator field terminal. ( Negative meter lead on the field terminal on the back of the alternator).
If all the connections between the battery and the alternator are good, you should read ZERO VOLTS. The more resistance there is, the more voltage you will have. The goal is ZERO VOLTS on this check.

Post the results of all these checks.

BC

Bill Curlee

While Im thinking about your issue, theres ONE other thing that I recommend that you check. Your ignition switch. Although it might NOT be the direct result of yor issues, it may be contributing to them. I have had 20+ people tell me that once they cleaned their ignition switch contacts, alot of their GHOST problems went AWAY!

Heres a link to the post that I recommend that you take a close look at:

http://forums.corvetteforum.com/show....php?t=1951626

Give that a try also.

BC