Calling all electrical experts- strange charging behavior

[SheepDog]

For the last couple of weeks, I have noticed some strange alternator/charging voltage behavior. When I initially fire up the car, all is well. I see around 13.5-14 volts on the gauge cluster display. After I drive for a period of time, maybe 30 minutes or so, the voltage when I am accelerating or even cruising with very little throttle input will drop down to 12.5 or even 12 volts. The moment I release the go pedal, the charging voltage jumps up to 14.5. However, if the car is moving and I shift into neutral, the voltage will again drop to 12ish volts. When at a stop light, clutch in or in neutral, engine at idle speed- 12ish volts. The only time I get charging voltage is in gear, car moving, full decel.

It almost seems as though the voltage is manifold vacuum dependent or maybe even heat dependent, which seems silly.
-One thing I considered is that perhaps the Alternator cannot keep up with the draw that 2 x 274 pumps pull when they get hot?
-perhaps something is going on with the throttle body/wiring?
-Maybe the alternator is shitting the bed, but it doesn't seem to have anything to do with engine speed. No matter the engine speed, as long as I'm off the gas but in gear, the alternator charges.



Car only has 8,000 miles
Battery is a brand new Odyssey AGM ( I replaced the OEM battery with this, because I thought the original battery was the culprit.)
When I start the car up from cold, I have full alternator output

Anyone had a similar problem, or have any ideas? This one has me stumped.

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[Mike Pfeifer]

Are you having an actual problem? It is normal for the voltage to fluctuate while driving.

 

[SheepDog]

Are you having an actual problem? It is normal for the voltage to fluctuate while driving.

Well, I guess I couldn't say for sure that it is a problem, accept that dropping down to 12 volts even, (12.0) when the car is running would indicate that the alternator isn't charging. I understand that the PCM varies the voltage, but I've never seen it at 12 volts when the car is running

It is very consistent, when I let off the gas, the voltage jumps to 14.5. The moment I get back on the throttle, it drops to 12.0 or 12.5.

 

[Blueflash]

I'm wondering about the battery monitoring system. Pretty sure its an extra cable attached to the negative post. I've heard of ppl with powerful stereos disconnecting it in order to recharge full time

 

[SheepDog]

I'm wondering about the battery monitoring system. Pretty sure its an extra cable attached to the negative post. I've heard of ppl with powerful stereos disconnecting it in order to recharge full time

Could be, but I have a new battery, and did the BMS reset. It is just strange that it is throttle dependent. If I am on the gas even 1%, it drops voltage, the moment I let off the accelerator, it jumps to 14.5 volts.

I've been driving it with everything the way it is for quite a while, but only recently noticed this voltage drop on Decel. I was thinking that maybe the fuel pumps (return system with 2x walbro 274's) was drawing more than the alternator can handle, and when off the throttle, the pressure regulator reduces pressure, thereby reducing amp draw from the pumps.

My understanding is that all cars that have the heated/cooled seats, also get the 200 amp alternator, but not 100% certain on that. It would be unlikely that the alternator is bad at such low usage, but not impossible.

I could try disconnecting the BMS sensor see if that changes anything

 

[Farkel]

This is perfectly normal behavior of the battery management system with a fully charged battery.
https://www.mustang6g.com/forums/threads/voltage-fluctuation.181614/#post-3664183

 

[Skye]

I'd seen this thread earlier, so took note of my voltage on a one-hour drive just now. Doing so though, I feel my comments are an apples-to-oranges comparison.

2022 Mach 1, EPA and air filter mod , but otherwise stock. Factory battery. Recaros. 6MT. If the car will not be driven for a few days or more, I connect a tender.

For the first 40 minutes, the voltage was so steady (14.5v) I stopped looking at it. It never changed, ever. About 45 mins in, for whatever reason, it stepped up to 15v for about five minutes, then stepped down to 14.5.

After a quick few gallons of gas, the voltage momentarily began at 14, but then stepped up to and stayed at 14.5v for the rest of the drive.

Driving mode, light mode, how driving, never had any direct influence.

 

[SheepDog]

This is perfectly normal behavior of the battery management system with a fully charged battery.
https://www.mustang6g.com/forums/threads/voltage-fluctuation.181614/#post-3664183

Thanks,

I've just never seen it do this before. The other issue with this behavior, is that the fuel pumps aren't getting the 13.5 volts that they're designed to run at, so at 12 volts, they give up somewhere around 15GPM each. I haven't taken a WOT log at 12 volts to see if the pressure and lambda are still stable at high rpm to know if that loss of flow is an issue or not.

 

[SheepDog]

I'd seen this thread earlier, so took note of my voltage on a one-hour drive just now. Doing so though, I feel my comments are an apples-to-oranges comparison.

2022 Mach 1, EPA and air filter mod , but otherwise stock. Factory battery. Recaros. 6MT. If the car will not be driven for a few days or more, I connect a tender.

For the first 40 minutes, the voltage was so steady (14.5v) I stopped looking at it. It never changed, ever. About 45 mins in, for whatever reason, it stepped up to 15v for about five minutes, then stepped down to 14.5.

After a quick few gallons of gas, the voltage momentarily began at 14, but then stepped up to and stayed at 14.5v for the rest of the drive.

Driving mode, light mode, how driving, never seemed to have any influence.

But the above is my car, my configuration. I'd think unless you're witnessing something weird, dramatic, or an unexplained change, I'd make note of it and press on.

Yeah, I've seen the same fluctuation previously. Changing from 13.5 to 14.5 but never dropping to 12.0. This effects my fuel pressure and flow rate, which is fairly significant for (2) 450 L/hr pumps.

However, the more concerning part is how this change is directly related to throttle input. Each and every time I have anything more than 0% throttle input, the voltage drops to 12. The instant that I get off the throttle, but the car is still in gear, it jumps to 14.5v. I can literally change the voltage on the display back and forth with simply giving it gas or not. Sitting at a stop light, engine idling I get 12 volts. The only time I see 14.5, is when the car is moving, in gear, but 0% throttle which is why I was saying on my original post that it somehow seems t obe manifold vacuum dependent.

 

[Farkel]

Yeah, I've seen the same fluctuation previously. Changing from 13.5 to 14.5 but never dropping to 12.0. This effects my fuel pressure and flow rate, which is fairly significant for (2) 450 L/hr pumps.

I'm not qualified to comment on things like fuel pressure and flow rate. I will only point out that the voltage displayed with the engine running is the alternator output to the battery, not the state of charge of the battery itself.

 

[Skye]

the more concerning part is how this change is directly related to throttle input

I'm currently qualified at the Fisher Price level . But I wonder if it's a function of the mods you have, specifically the pumps and their load as the throttle (and injector flow) changes. Not that it's bad or anything. The car seems to be working fine. But for your car, the current config, that's what is is? Someone with aftermarket pumps, their voltage and load characteristics (and how wired to the car) would have to comment on that. Maybe the maker of those pumps could provide feedback as well.

 

[SheepDog]

I'm not qualified to comment on things like fuel pressure and flow rate. I will only point out that the voltage displayed with the engine running is the alternator output to the battery, not the state of charge of the battery itself.

Fully understand that. However, the concern for me is that the alternator output voltage on the display in this scenario, is directly proportionate to throttle input. 0% throttle but in gear and decelerating, I get 14.5 volts. The moment I tip into the throttle, the voltage on the display drops to 12 volts.

 

[SheepDog]

I'm currently qualified at the Fisher Price level . But I wonder if it's a function of the mods you have, specifically the pumps and their load as the throttle (and injector flow) changes. Not that it's bad or anything. The car seems to be working fine. But for your car, the current config, that's what is is? Someone with aftermarket pumps, their voltage and load characteristics (and how wired to the car) would have to comment on that. Maybe the maker of those pumps could provide feedback as well.

Thanks for the response. This is something I was considering, but I have had this fuel system on the car now for 18 months or so, and only recently started seeing this strange voltage -per-throttle behavior. Im not talking about WOT. Just cruising along on the highway, if I have even 5% throttle, I get 12 volts. The instant that I let off the throttle but still in gear, I get 14.5 volts. If I throw it in neutral, but the car is still moving down the road, again I get 12 volts. It really does seem to be manifold vacuum dependent, which obviously doesn't make sense to me.

 

[Farkel]

Again, this sounds like normal behavior controlled by the BMS. It's a feature, not a bug. If you were seeing consistently higher readings with your old battery, it might have been due to the deteriorating condition of the battery.

 

[Mike Pfeifer]

You could discharge your battery and go drive around to see how it behaves, I will bet money on it staying on higher voltage more often. Maybe constantly, till it’s happy about SOC.

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