I have put in a new battery.

I am seeing 11.7 volts in the dash. If I check the battery with a multi-meter I am seeing 12.3 volts, if I check at the back of the alternator and the ground on the drivers side in the engine bay I am seeing 13.8 volts to 14.3 volts. This is only with running lights on (no air conditioning).

Summary: car thinks 11.7, battery thinks it is 12.3 and alternator thinks it is 14.3.

I pulled the fuses in the engine bay for the start (40 amp fuse) and put it back. I changed it with an another 40 amp fuse too. No change. I checked the connections on the battery when I replaced it.

The car has some times been clicking from the starter, but other times not. Sometimes the car will show 11.7 volts on the dash and then after a minute or so climb to 14.3 like the alternator is charging the battery.

Is there a way I can isolate what might be causing this? I would like to be able to say it is the alternator, starter or electrical connections before I start replacing them.

 

The voltage inside the car will always be .4 to .5 volts lower than at the battery…sounds like you have a voltage drop of 2 volts on the charging system…alternator voltage minus the battery….you will need to check if it is on the positive or negative side of the charging system…to check positive side and running the car at 2500 RPM with electrical loads on it connect your voltmeter between battery positive and the other lead to alternator B+….don’t worry if you see a minus voltage but just look at the number…now do same thing between battery ground and the alternator case…if over .3 volts (.5 is factory number) you have high resistance…on positive side can be down at the starter solenoid where the alternator cable and battery positive cables are connected…both cables should be removed and cleaned as well as the stud and remember to remove battery negative first !!…I use a small wire brush…if negative side is excessive you need to remove the battery negative cable and clean that…you may need to remove the starter….also do a voltage drop between each battery post and the terminal and between alternator B+ stud and the lug…on my car I see .32 on positive side and .10 on negative side…you should remember when the car if off battery negative has the most negative “potential” and when running it is the alternator case…and think of your voltmeter as a “difference”meter…it can be hooked to any spot on the car whether both on positive or negative sides of the car…your clicking symptoms suggest it is the connections at the starter.

 

If you have those crappy OEM terminals and you have mechanical skills cut them off and swage some copper lugs on your battery terminals.

 

For a quick check, take a look at the cable connections on the starter solenoid. It's not uncommon for them to loosen up or for the area around the post to get brittle and break up - particularly if the car has headers. There is also a large ground cable on the block nearby that is worth checking on while down there.

 

Check battery terminals, clean all grounds, Big 3 wiring, Powermaster 9509 starter with DEI starter shield, and a Mechman 170 amp or 240 amp alternator. You'll never have another issue.

I had similar issues with voltage drop especially with A/C running and in reverse volts would hit low 11v's and want to stall. Did all the above and never drop below 14v now.

 

If problem is not down line of alternator, Hence power goes from alternator, through starter terminal, to battery, battery to engine fuse box, engine fuse box tto BCM through is connector, then down line to modules like ECM that could just be one of the connectors or mondules in that pathway that need to be cleaned and greases,


But in the alternator itself (checking voltage at back alternator terminal), then may want to give this a read, since could be as simple at bad connector or binding bushing in bushing housing the problem instead.
https://www.corvetteforum.com/forums...nator-fix.html

Now having stated all this, keep in mind that oem valeo 140amp alternator only puts out about 14 amps as idle, the raditor fan that the HVAC system is going to turn on will draw about 18 amps, so if sitting at stop light long enough, the battery is being drained down/alternator not keeping up with demand, and could be up to 15min with the engine back at over 2K before the battery is charged all the way back back up. So with all the connectors, grounds cleaned, and the alternator cleaned up so is back to factory fresh, the voltage dropping while sitting at a stop light long enough, is still going to be a problem with the HVAC system on.
If this is the case, and you have checked and cleaned the rest and still have problem, then may be time to upgrade to a billet mechman 170amp 6 pole alternator that will put out 45 +amps at idle, that will keep up with system demands. Also, big three cables is not a bad mod as well. Alternator is about $440, the cable mod is about $130 in parts, but with charging system keeping up with cars needs, your batteries is going to last a hell of lot longer each time instead.

And FYI, the stock valeo alternator was not only for value engineering to keep price down on the car build, but less drag on the serpentine belt,to allow the engine to make more power as well. So just keep that in mind, that you will be giving up a few HP with the mechman alternator installed, but giving up even more HP with the HVAC system running in the first place.

 

The only thing is the circuit that could be causing this issue is the fusible link down by the starter. It is a pain to replace. GM would replace the harness that this is part of. It goes from the charging terminal of the alternator to the starter through the engine harness. Last one I did I just ran a new wire from the alternator to the starter with the fusible link added to the starter end.

Gary

 

Thanks for the detailed reply. I couldn't work out where the lead to the alternator was (the back of the housing?) and the battery ground is the one by the alternator?

I ended up working on something I could control and cleaned the battery terminals and the grounds under the battery. No change in car's behavior. I will get under the car tomorrow and look at the starter.

 

Yes, alternator B+ is the big red wire on the back of the alternator…this is not a ground issue that everyone tries cleaning to fix their car…battery ground is the black cable at the battery…battery positive is the red cable…if this is over your head please seek out a shop that does electrical work.

 

Guess I can't 'like' that last post more than once...

 

No worries. I am doing this to learn. Appreciate your patience in explaining it. I have the multi-meter set at 20DCV.

Battery+ to alternator B+ is 2.93V
Battery ground to alternator case is showing 0

I think it is the alternator, now when the car is running the battery is not charging, it is sitting at 11.3V. Last week the car would jump up to 14.1V after 30 to 45 seconds or so after starting. Now it is not doing that.

Cam

 

That means you are dropping 2.93 volts between the alternator and battery…you should disconnect the negative battery terminal first and get underneath the car and check the 2 positive cable connections at the starter solenoid…either the nut is loose or you have some corrosion…I’d remove both and clean up the terminal lugs and the post with a small wire brush !!…you should first check between the positive battery post and the terminal also.

 

With the car running place red lead of voltmeter on the stud at the alternator and other lead on the alternator case…see what you read.

 

It is getting 14.1V to 14.2V.

Does that suggest the issue is between the battery and the alternator?

 

That means your alternator is fine !!…yes, most likely down at the starter.

 

Cool, thanks for all your help. I will get under the car, clean those connections and report back. Thanks again.

 

Look at the starter…both cables are attached there…REMEMBER TO DISCONNECT THE NEGATIVE BATTERY TERMINAL !!

 

Took the battery out to be safe

This is a photo of the starter. I guess I am going to have to remove part of the exhaust to get in there. It is pretty rusted.

 

Just remove the nut that secures the 2 cables and then remove and clean them reinstall…you don’t need to remove the starter…I did this last month and took less than 5 minutes.

 

ok. Thanks again.