Electrical Voltage Drops

[Coderedsaleen]

took my car to the dyno today and here is a problem that we ran into. I hope someone will be able to help out?

We ran the car on the dyno and during a pull, at 5150 rpms, voltage dropped to 10.5 volts on the laptop, which in turn makes everything else go haywire. We put a voltmeter on the back of the alternator to make sure that it was not the problem. We did another pull and once again the voltage on the laptop dropped and the same mess again. The voltmeter attached to the alternator dropped to only 12.3 volts. This should rule out the alternator? So the question is what would make the happen and how can I fix it?

Here is a pic of the mess during the pull. Check out that crazy horsepower line, LOL.

 

[spincobra03]

I work as a control technician and not being there makes it difficult to say but with the info your giving me, I would not rule out the alternator just yet. What are your mods? Do you have an alternator pulley on already? Whats exactly going haywire? How many volts DC are you supposed to have at full load? There are alot of possible contributing factors

 

[spincobra03]

lol I see what is going haywire, but did you notice an issue with the car? What prompted you to bring it to the dyno? The reason I ask is im wondering if there could be an issue with his computer, or cords?

 

[Coderedsaleen]

I work as a control technician and not being there makes it difficult to say but with the info your giving me, I would not rule out the alternator just yet. What are your mods? Do you have an alternator pulley on already? Whats exactly going haywire? How many volts DC are you supposed to have at full load? There are alot of possible contributing factors

Mods: 2.8 Pulley
CAI
Ported Blower

Haywire: When the voltage drops to 10.? volts the duty cycle of the fuel pumps drops off, the MAF drops off, and leans out because of it.

Volts: The volts are suppose to be maintained at 12.5 or higher. The alternator never drops below 12.3 volts at the same rpm's the PCM voltage drops off to 10.? :shrug:

 

[Coderedsaleen]

lol I see what is going haywire, but did you notice an issue with the car? What prompted you to bring it to the dyno? The reason I ask is im wondering if there could be an issue with his computer, or cords?

I brought it to the dyno to get tuned after I did the engine conversion, now I'm sure I will get alot of questions. LOL. I swapped a 2001 2V S/C for a 2003 4V S/C.

 

[KILRSVT]

you can probably still tune it.... hooking a power supply to the car... maybe the altenator is not putting out enough voltage to overcome the resistance of the wiring...my puts out 14.1 volts consistently......maybe your altenator is weak...since the duty cycle increases with rpms due to the deamnd of fuel and timing....your alt probably cant keep up...

 

[Coderedsaleen]

you can probably still tune it.... hooking a power supply to the car... maybe the altenator is not putting out enough voltage to overcome the resistance of the wiring...my puts out 14.1 volts consistently......maybe your altenator is weak...since the duty cycle increases with rpms due to the deamnd of fuel and timing....your alt probably cant keep up...

I have 13.8 most of the the time but drops as the RPM's go up during the dyno pull. When we did the pull it drop to 12.2 on the alternator and the laptop read 10.5 on PCM. I had the alternator tested and they all say it is good. Maybe I will see about changing that out since it may be the root of the problems for voltage. It could be on its way out? :shrug:

 

[KILRSVT]

it could be that the voltage regulator in it is going out..got a similar issue on my car but i just replaced my altenator....with a non oem rebuilt....so gonna order one from tousley....i believe they run for 160.,,good luck

 

[Coderedsaleen]

it could be that the voltage regulator in it is going out..got a similar issue on my car but i just replaced my altenator....with a non oem rebuilt....so gonna order one from tousley....i believe they run for 160.,,good luck

I think I might just go ahead and order one so I can eliminate it from the equation.

 

[KILRSVT]

for sure.....good luck. keep us posted

 

[spincobra03]

Yeah thats whats making me think its the alternator starting to crap out. The reason being IMO, is when the load increases (i.e. rpm's increasing), a strong alternator should not drop voltage like that. Does it have an upgraded alternator pulley? Even though it will cost you a few bucks, I would change the alternator, but get another opinion first.

 

[spincobra03]

Mods: 2.8 Pulley
CAI
Ported Blower

Haywire: When the voltage drops to 10.? volts the duty cycle of the fuel pumps drops off, the MAF drops off, and leans out because of it.

Volts: The volts are suppose to be maintained at 12.5 or higher. The alternator never drops below 12.3 volts at the same rpm's the PCM voltage drops off to 10.? :shrug:

oops sorry I didnt read this post fully, even though you arent getting the drop right at the alternator, to me dosent completly rule it out. But after reading this im starting to worry and wonder if the problem is deeper than that. Ill run the problem by someone today with VERY good mechanical backround to get his 2 cents.

 

[Coderedsaleen]

oops sorry I didnt read this post fully, even though you arent getting the drop right at the alternator, to me dosent completly rule it out. But after reading this im starting to worry and wonder if the problem is deeper than that. Ill run the problem by someone today with VERY good mechanical backround to get his 2 cents.

Thanks. I have also heard that I may have a ground problem. I have the electrical diagram manual for the car so I am going to check those also to see if I can rule out the grounds. I think that it is the alternator personally because like you said with the higher RPMs the alternator might not be able to keep up. It has a stock pulley on it so it shouldn't be over spinning it. I always read on the forums that these alternators are notorious to have some sort of problem.

 

[mmustangsrus]

Mods: 2.8 Pulley
CAI
Ported Blower

Haywire: When the voltage drops to 10.? volts the duty cycle of the fuel pumps drops off, the MAF drops off, and leans out because of it.
Volts: The volts are suppose to be maintained at 12.5 or higher. The alternator never drops below 12.3 volts at the same rpm's the PCM voltage drops off to 10.? :shrug:

you better get a alt or keep a serious eye dont want be buying a new motor

search on here for "alt falures" thats killed plenty of motors mine being one of them

good luck :beer:

 

[spincobra03]

Ok since you dont have a lower pulley you shouldnt need an alternator pulley. When you add a lower you need to change the alternator pulley.
Yes definetly check any ground wires that could possibly be in that circut. Cant you take the car to your mechanic and have him check the alternator to see if its good?
Keep us posted