voltage variation at idle

[MPGmustang]

honestly I see it consistant, but what do I know...

The only issue that I can see is your voltage changed from 13.1 to 14 volts and the engine sped up. There is different injector pulse etc. based on voltage. This should not be jumping like this at idle, should stay either 13 volts or 14 volts but not jumping between the two.

AFI tuning needs me 'to fix or look into the voltage variation at idle'
driving voltage is 14.1-14.2, anything less than 1050rpm the voltage drops lower than 13.8, lowest I've seen is 13.1 on idle @ 850rpm.

now for the belts I have one on "HB to WP to AC" belt, then a 2nd belt from "AC to ALT". could it just be spinning too slow for my 14.1 volt idle?

this is VERY consistant to drop voltage down at idle, but I think I should still look into it...

I'm using an eBay 100amp chrome 3wire alt that I got for like $90, it came with it's own regulator, think I should just change the regulator? or both? I'm actually thinking this isn't 'truely' a 100amp alt either, just 'chromed' and sold as 100amp. I'm tempted to go get a car-quest alt and regulator as they have never failed me before in quality parts, unlike lifetime replacement of autozone/0riely's/napa...

but what do you guy's think? will this be strictly alt and reg, or you think my 50yr wiring is getting to me?

 

[Asa]

Sounds to me like someone is trying to sell you a bridge.
The 13.1 sounds a little low to me, but 13.8-14.2 due to RPM change sounds fine

 

[MPGmustang]

13.8 is roughly 1150 rpm, anything below 1050 is where it's down to 13.1...

a bridge??? not familiar? maybe 'ripped off'? scammed?

 

[Asa]

"I've got a bridge in San Francisco that I think you'd like"

Ideally, once you get a load on the engine you should get a stable voltage reading. It sort of depends on what electrical load you have on the vehicle, lights on, electric fan, AC system, etc.

 

[MPGmustang]

yes, once there is work, or the RPM is higher, it's loads just fine and the voltage is stable, it's only while idling that it drops, it's constant while driving, but only at stop lights it dips low... until I hit the gas again. this will even be during the day, I always have AC on, as it's hot, I'll have to try a hot ride sometime and see if it's the AC that's droping my voltage when I idle.

 

[thesameguy]

This is just a pulley issue then. You aren't driving the alternator fast enough to generate enough voltage at idle. You need a smaller pulley on the alternator, or a bigger pulley on the crank, or an alternator with a lower minimum speed. 13.1v isn't inherently an issue, but that will depend on what you're running - the more electrics you have on at idle, the riskier it will be.

 

[MPGmustang]

thesameguy-
I'm running AC, lights, radio, and TBI fuel injection (electric gas pump included) using a mech fan.
the ALT is ran off the AC pulley, like I stated earlier, I can only replace the ALT pulley or the ALT. replacing the AC pulley is difficult.
the concern is for the ECM to see one voltage, as it uses a 'different injector pulse' depending on voltage.

 

[Asa]

That... that doesn't make sense to me
The TBI doesn't see reference voltage? Virtually all computer driven injection systems I have seen see a 5v reference at sensors and motors and such. Yours might be a slightly different setup, but the injector should still be opened directly from the computer, which should be a set voltage, not the battery/charging system voltage.

 

[InlineDave87]

Have you considered seeing if you can install a smaller pulley? A smaller pulley would make it spin faster tricking your alternator that its at a higher rpm than it really is and the regulator should keep it from producing too much voltage. Or you could see if your HB pulley is bigger than the alternator, you can run a belt from there to do the same thing to speed up alt rpms. Aside from that you usually should see an increase of at least .5 volts when increasing engine speed to around 1500 rpms and ideally you want idling charging volts at 13.5. Hope this helps.

 

[thesameguy]

Agreed. Battery/charging voltage should have nothing to do with what the ECM/ECU/PCM/whatever you want to call it is doing - unless of course charging voltage drops below 8 or 9v, and there simply isn't enough juice to run the ECM in the first place.

I would warm the car up, start everything electrical you can, and see what your charging voltage is like at idle. If it's above 12.5v, you're probably just fine. If it stays at 13.1v, you are totally fine.

 

[xctasy]

I'm a veteren of about 7 years with Delco's P4 on wobbly old Buick bent sixes, I know its low battery behaviour well. We used two wagons, one was my mate Robbies 1993 Commodore Berlina for the Otago Sports Car Rallye, where we'd sit around for 1/4 of the day with the lights on dip, and the radio on, and sporadic engine starts. The other the poverty spec 1993 Commodore Executive wagon for the consultancy.

EEC5 and Delco P4/Calpak/Memcals are all like that. Each of the wagons used a port injected GM 3800 . The car ran like SH!+ if the battery wasn't in good trim. Lockup clutch would be rough, the idle would be choppy, the coil pack ignition seamed to miss, power steering would get lumpy on a V6 because the idle speed would surge and give the old balance shafts a good old work out. Yet the Cal Pack car would still start with a bare minimum charge.

Same with the nearly as old Cologne V6 in my Explorer, when it had an old stand in marrine battery for the first year, runs awfully when the battery is in bad trim, and especially when you start pulling power out of the alternator circuit. Since you'd be running the truck constantly, you only needed to start the car on a nearly flat battery, then it'd run all the time. EDIS ensures it will always at least start even when the battery was almost dead.However, if battery voltage failed to allow the alternator to pour the amps back into the battery, the idle and general give and take low end drivability then became awfull, especially in a 5 speed auto where the lock up clutch and gear changes were based on having a bare minimum charge present. It would be jerky, obtrusive, and a pain to drive around hilly suburbs or give and take low speed country roads.

Its EDIS, the engine and trans control ECU's get hammered big time when the drag from the A/C, ps and the big ass 3G alternator that cant keep up with a langishing battery that do it.

A new battery, and the Exploder has been just brilliant ever since, tractable, docile, a different animal entirely.

For State Highway inspections, I'd run a 300 W invertter for the camera battery charger, printer for defects, a spot light for night drive overs, two amber lights with four 55 w bulbs all told, a lap top for the position and gps readings, and that would take a fair toll on the low rev performance.

The same load, plus an additional data logger doesn't even hurt the 3.3 carby Mustang one bit, even with out the extra battery I have on offer.

 

[MPGmustang]

okay, aside from ECM... this is weird...

get the logger out, hooked up, start logging, key to run, check screen and see volts is down to 11.5, start car running, 2700rpm, volts 11.5, shut car off, car to run, 11.5, start car, 11.5, 2700rpm, drive all the way to work, 11.5....

what would make my car not charge? something is fishy, something doesn't make sense... please help

it is an older battery, maybe I need my newer one, I'll get that in and drive around for a bit... maybe it's simply the battery...

 

[Asa]

At 11.5v, there should be no reason for the alternator to not generate a field and start charging. Sounds like now you've got an issue with the charging system.

If the shop you took it to tried to fix whatever charging problem they thought they saw, they might've unplugged something and left it unplugged. I'd go through everything and see if it all is hooked up correctly

 

[MPGmustang]

I never take it to a shop, I do all the work myself...

nothing is unplugged, and everything is secured... I thought the same that something came loose.. but I can't find anything... think it's the alt?

 

[Asa]

I assumed that AFI Tuning was a local shop.

'65 should still have the external regulator and I'm shaky on how those function within the system. Either going to be the Alt or Reg, you should be able to take the Alt into any local place and have them test it

 

[InlineDave87]

SMH... A battery life span is only for 5 to 7 years... longer than that and its pushing it... If the battery looks bloated or gets very hot with current flow really fast... its bad... and that could cause it to look like the alternator is bad when it is not... in sort a false positive

 

[MPGmustang]

okay guy's here's a riddle for you...

11.5 volts,

Replaced the following
ALT
REG
Battery (previous bat was a 6-2005 this one is a 3-2012)

I still have 11.5 volts... I think something is up with the wiring... but where?

 

[bubba22349]

That low of voltage could cause problems with the ignition and TBI. What voltage do you get for the battery itself (unhooked)? If they are the wet cell battery's have you tried doing a specific gravity test of each cell or a load test on your battery's? Is there any other electrical items that have been added beside the stock parts, TBI, and DUI like a direct wired amp

 

[MPGmustang]

that's what I was thinking... I don't want to hurt anything... so I'm waiting and testing... no prolonged unnessesary driving...

I didn't drive it today, nor have I checked the battery voltage...

just the TBI, ignition, AC (so AC comressor, and blower)

I unplugged the radio fuse (it's always on, unlike ignition only...) and I'm running HID headlights but not during the day.
I'll try unplugging the AC compressor and Blower fuses, see what that does... then I'll try the head light fuse. If anything changes I'll know.

but with nothing running on the car (engine off, AC off, blower off, head lights off, radio off, foot off brake, turn signal off, parking lights off... ect) it still show'd 11.9v maybe 12, but running it goes to 11.5, and this is what the ECM sees, it shows on my laptop (the laptop supplies USB power to read, so the ECM doesn't need to give extra juice)

 

[xctasy]

I adjusted the tension on my twin belt A/C/Alt section, and the battery volts changed from 11.9 to 13.5 just by going from 0.75" belt preload to 0.5".Just check the obvious again.