Voltage drop - I think I know, but tell me

[Jerryl]

I “think” I know the answer , but tell me what you think.

This is on a Non-IC’d car but still :tongue:
At idle, the battery voltage on PL reads 13.5-14
When getting into boost, voltage drops to 12.5-12.8, and as soon as I get out of the throttle, voltage goes back to 13.3+

Battery is fresh, alternator is stock NAPA replacement 96A with 1000-1500 miles.
No accessories running, ground cables clean/tight, HW Denso, PAC, WB.
No starting problems, no hick-ups. misfires, or other issues.
FP with the Denso (on PL) is rock steady.
I can not think of anything drawing that many amps!

I am guessing (Conservatively not sure on any of these)
HW Denso – 15-18A
PAC – 15-18A
WB – 5-8A
Ignition / ECM etc. – 10-15A

At night, with the lights on, the voltage drop is an additional 0.3 - 0.5 V
Also noticed(consistently); The higher the boost, the lower the voltage.

Is this the reason GM went to a higher output alternator on the IC’d cars, or, do I ignore the reading of PL?

 

[TurboDave]

Could be the alternator not being able to keep up.

Also, see that one wire that runs from the lug on the back of the alternator over to the battery? That's the main charge wire, and IMHO is far from sufficient when ANY upgrades are on the car.
You might think about upping the gauge on that wire by at least 4 steps. I think I'm running at least a 4 ga. wire there. Some use larger. I think stock wire is like 10 or 8 ga.
That alone might help. If not, you might think about an alternator upgrade.

 

[Jerryl]

Could be the alternator not being able to keep up.

Also, see that one wire that runs from the lug on the back of the alternator over to the battery? That's the main charge wire, and IMHO is far from sufficient when ANY upgrades are on the car.
You might think about upping the gauge on that wire by at least 4 steps. I think I'm running at least a 4 ga. wire there. Some use larger. I think stock wire is like 10 or 8 ga.
That alone might help. If not, you might think about an alternator upgrade.

Thanks Dave!
PS; I already added an extra 8 gauge wire from the alternator to the battery and an extra ground cable from the battery to the body.

 

[jasjamz]

I thought the powerlogger reads ECM voltage. I think you may find a slightly higher reading at the back of the alternator during your 25psieek: ) runs. I get the same readings and use the 140 amp Impala SS alternator.

 

[Tony Shoaff]

Mine is the same also?? We have tried and tried to find the answer??

 

[Mad_Trbo]

Alternator

I would tend to think it is the alternator not being able to keep up.

How are all of your ground straps?

 

[notacarlo]

Do You Have An Underdrive Pulley?

 

[Tony Shoaff]

I dont think. RJC Aluminum pulley?

 

[Jerryl]

I thought the powerlogger reads ECM voltage. I think you may find a slightly higher reading at the back of the alternator during your 25psieek: ) runs. I get the same readings and use the 140 amp Impala SS alternator.

Interesting with the 140A alternator.
Understand that the voltage is at the ECM, but I still see a voltage drop.
Anything 12-13V is not a good thing on a TR.
Not sure how I verify/log voltage at the alternator, at 65+ MPH. Any ideas?

I would tend to think it is the alternator not being able to keep up.

How are all of your ground straps?

Ground straps are ok. Cleaned and tight.

Do You Have An Underdrive Pulley?

I dont think. RJC Aluminum pulley?

Stock pulley - Hot Air

 

[A2000RICH]

Interesting with the 140A alternator.
Understand that the voltage is at the ECM, but I still see a voltage drop.
Anything 12-13V is not a good thing on a TR.
Not sure how I verify/log voltage at the alternator, at 65+ MPH. Any ideas?


Ground straps are ok. Cleaned and tight.



Stock pulley - Hot Air

run two small gauge wires from inside the car, out the window and into the engine comp-------connect them to the alternator output post and case directly-------hook the other end to a volt meter inside the car and read it when you are driving--------odds are that it will be just fine-----that indicates a drop somewhere in the harness between the alt and ecm..............RC

 

[Jerryl]

run two small gauge wires from inside the car, out the window and into the engine comp-------connect them to the alternator output post and case directly-------hook the other end to a volt meter inside the car and read it when you are driving--------odds are that it will be just fine-----that indicates a drop somewhere in the harness between the alt and ecm..............RC

Thanks Rich!
I was just concerned that the pump and ignition were not getting the voltage they require.
I will run some wires and connect them to my VOM.

 

[Tony Shoaff]

Thanks Richard I will do the same.

 

[turbofrank]

volt booster

 

[95' regal gs]

Bare in mind that I'm no expert but..... I do know that some vehicles have a "load shedding" logic in the ECM/PCM. When the vehicle is in WOT conditions non-essentials are turned off or limited, A/C, alternator HVAC ect... Because WOT operation is normally short, this can be done. I don't know if this system was around when these cars were built but, just a thought.

 

[Tony Shoaff]

Very Possible? 95 regal gs. Anyone??

 

[WSLN 6]

I had the same type of problem on my car. Cleaned up connections (multiple hotwires on alt.) and my voltage at WOT is now 13.4+ out of the ecm. sed a Caspers coil pack tester and only 1 bank out of 3 would be firing at idle, yet it had over 12 volts going to it. Removed coil pack and repeated the test off the car, worked perfect....hmmm.
Found a splice from my alternator over to the main battery wire that had gone bad, and bled off voltage under load. Replace your positive battery cable going to your starter. I now have 14.4 volts coming out of the ecm at idle.
I also reterminated my ecm orange power wire under the hood.
Some places to look!

 

[Tony Shoaff]

I wonder if it is from over revving the alt?? I have the battery in the trunk. Large cable's, 2 grounds for battery, one from battery to Pass head ground bolt other to frame. Ground from engine to frame. 6 gauge wire from alt to battery.

 

[brian]

Jerryl,
I found the regulator is different/special for the Buicks. The 95 Impala shares the same reg. As rpm increases, my volts were droping as well.
Get a stock regulator from a dealer and have it installed. I am quite certain you are seeing the same thing I did.
Put a good stocker on and see if it does not do that any longer.

Putting a stock unit back on fixed this issue. A buddy of mine tracked down good used regulators at and alt shop, and had it installed.... Problem solved.

 

[Jerryl]

Thanks for all the input fella's

Jerryl,
I found the regulator is different/special for the Buicks. The 95 Impala shares the same reg. As rpm increases, my volts were droping as well.
Get a stock regulator from a dealer and have it installed. I am quite certain you are seeing the same thing I did.
Put a good stocker on and see if it does not do that any longer.

Putting a stock unit back on fixed this issue. A buddy of mine tracked down good used regulators at and alt shop, and had it installed.... Problem solved.

Thank Brian!
Is this buddy of yours running a HA?

The HA uses a special 12SI 96A alternator, and I am unsure if I can locate a OEM regulator for this. I will call the dealer. (Where is Turbofish???? :biggrin: )

This new alternator I got is "supposed" to meet OEM specs, and marked "96A".
I know it is special, because it had to be ordered by NAPA.
Autozone and OReilly did not carry an alternator for this car, but had plenty of 60A, 80A units.

I am wondering if this "low ECM VOltage" is the reason GM went to the bigger output alternators (besides the addition of electric fan) on the 86-87?

I had the same type of problem on my car. Cleaned up connections (multiple hotwires on alt.) and my voltage at WOT is now 13.4+ out of the ecm. sed a Caspers coil pack tester and only 1 bank out of 3 would be firing at idle, yet it had over 12 volts going to it. Removed coil pack and repeated the test off the car, worked perfect....hmmm.
Found a splice from my alternator over to the main battery wire that had gone bad, and bled off voltage under load. Replace your positive battery cable going to your starter. I now have 14.4 volts coming out of the ecm at idle.
I also reterminated my ecm orange power wire under the hood.
Some places to look!

Thanks! :biggrin:
I will go back and look into the suggestions.
As stated previously; The car has no miss, no starting issues, etc.

Bare in mind that I'm no expert but..... I do know that some vehicles have a "load shedding" logic in the ECM/PCM. When the vehicle is in WOT conditions non-essentials are turned off or limited, A/C, alternator HVAC ect... Because WOT operation is normally short, this can be done. I don't know if this system was around when these cars were built but, just a thought.

I am positive my TT chip does the same thing, i.e. turning off accessories under load. Thanks for the input!

 

[jasjamz]

I had the same type of problem on my car. Cleaned up connections (multiple hotwires on alt.) and my voltage at WOT is now 13.4+ out of the ecm. sed a Caspers coil pack tester and only 1 bank out of 3 would be firing at idle, yet it had over 12 volts going to it. Removed coil pack and repeated the test off the car, worked perfect....hmmm.
Found a splice from my alternator over to the main battery wire that had gone bad, and bled off voltage under load. Replace your positive battery cable going to your starter. I now have 14.4 volts coming out of the ecm at idle.
I also reterminated my ecm orange power wire under the hood.
Some places to look!

Great...Now I have to get the heater out and try your suggestions:biggrin:
To the garage I go!