Riddle me this...?

[tank86]

Okay here's how it works. Truck has like a 135amp alternator so it should fully charge even at idle.

Your voltages look okay until you turn on the A/C .. Could load from A/C compressor and/or alternator be causing belt slip ? Is electrical load causing slip or showing a defective alternator ? Or is the load showing bad wiring on the regulator or even alternator output ?

The alternator uses a voltage regulator that's built into the PCM !!

So since you have low voltage under a bigger load it's a pretty short list :
alternator bad
belt slipping
PCM weirding out
bad [ie corroded / cracked / shorted / etc ] wiring

Try an amp meter on the alternator + and see what you get under your A/C load and no-load. That might point you in the right direction. If you get really crazy you can monitor the voltage on the regulator+ input to the alternator. As it approaches system/battery voltage the alternator is at full output. If the reg voltage is high and the alt output is low then you've isolated the issue to bad alt or belt slip. Could end up being something almost unrelated like a bad A/C compressor causing belt slip.

--CC

I appreciate the feedback. I am just chasing a unicorn at this point it feels like. I just replaced the alternator, so hopefully it isn't that but I will check anyways.

Ok, so I ALWAYS have AC on. Well tonight as I was sitting at the drive thru I had it off with windows down. The fan kicked on (electric fan) to cool down and I noticed my voltage dropped as soon as I heard the fan kick on voltage plummeted. That would rule out AC compressor then and belt slip, correct? Would lead me to believe wiring or alt?

This is way over my head so I am just bouncing ideas.

 

[ZCx]

if it is belt slippin, have ya noticed any difference in the p/s???

just for S&G's, ya could try runnin a ground wire off the alt. straight to the neg. on the batt. that would rule out ground issues. & yes our voltage regulators are controlled through the ECM, controls ground.

agree with ya on the a/c comp. ohms on the clutch should be bout 3.2ish. e fans do pull some juice

what year is your beast??? crank pulley?????

 

[VENOMOUS1 RACING]

Can you borrow another battery to try?

 

[CaptnCrash]

I appreciate the feedback. I am just chasing a unicorn at this point it feels like. I just replaced the alternator, so hopefully it isn't that but I will check anyways.

Ok, so I ALWAYS have AC on. Well tonight as I was sitting at the drive thru I had it off with windows down. The fan kicked on (electric fan) to cool down and I noticed my voltage dropped as soon as I heard the fan kick on voltage plummeted. That would rule out AC compressor then and belt slip, correct? Would lead me to believe wiring or alt?

This is way over my head so I am just bouncing ideas.

The fan is run via the power steering pump it's not electric assuming you have not changed it out. A P/S pump could also make that belt slip. If it is now electric, that points to a belt / tension or wiring. New alternators just don't magically fail in a few weeks.

--CC

 

[VENOMOUS1 RACING]

The fan is run via the power steering pump it's not electric assuming you have not changed it out. A P/S pump could also make that belt slip. If it is now electric, that points to a belt / tension or wiring. New alternators just don't magically fail in a few weeks.

--CC

Yip he has electric fans.

 

[tank86]

Can you borrow another battery to try?

I am going to see if anyone has one.

Just for my own general education, low voltage at start up would indicate battery, but what about while it's running? Doesn't the alternator take over after start up?

 

[tank86]

if it is belt slippin, have ya noticed any difference in the p/s???

just for S&G's, ya could try runnin a ground wire off the alt. straight to the neg. on the batt. that would rule out ground issues. & yes our voltage regulators are controlled through the ECM, controls ground.

agree with ya on the a/c comp. ohms on the clutch should be bout 3.2ish. e fans do pull some juice

what year is your beast??? crank pulley?????

Hmmm, I might try that running a ground wire from alt to ground. Haven't noticed PS issues, well anymore than it normally has from the electric fan conversion.

Ok, I'll google how to read ohms from ac clutch.

It's an 04, I checked the crank bolt to make sure it wasn't loose.

 

[Viper83101]

I am going to see if anyone has one.

Just for my own general education, low voltage at start up would indicate battery, but what about while it's running? Doesn't the alternator take over after start up?

Yea Zac, the alternator takes over and runs all electricals once the truck is running. The battery is only there for startup and in turn will also keep the battery charged. As long as your battery is good to start your truck then the problem isnt in the battery. If your alternator isn't putting out the correct power whether it be the actual alternator or wiring issues then you will have all kinds of problems. I honestly feel like its either the alternator or the wiring/connections somewhere. Also, dont rule out the alternator just because its brand new...I have seen them bad right out of the box. I feel like once you can get an amprobe (amp clamp meter), then you will be able to find out your problem.

VENM505

 

[tank86]

Yea Zac, the alternator takes over and runs all electricals once the truck is running. The battery is only there for startup and in turn will also keep the battery charged. As long as your battery is good to start your truck then the problem isnt in the battery. If your alternator isn't putting out the correct power whether it be the actual alternator or wiring issues then you will have all kinds of problems. I honestly feel like its either the alternator or the wiring/connections somewhere. Also, dont rule out the alternator just because its brand new...I have seen them bad right out of the box. I feel like once you can get an amprobe (amp clamp meter), then you will be able to find out your problem.

VENM505

I just don't understand how at idle voltage can plummet and shoot back up when driving. Could bad wiring really do that? I keep thinking maybe belt is getting resistance or slipping?

Oh, and side note, i hear a clanking/slapping sound underneath. Yay me...

 

[tank86]

Apparently it was low before I bought it? Just cycling through pics.

 

[Viper83101]

I just don't understand how at idle voltage can plummet and shoot back up when driving. Could bad wiring really do that? I keep thinking maybe belt is getting resistance or slipping?

Oh, and side note, i hear a clanking/slapping sound underneath. Yay me...

A bad connection/bad wiring can make it do some really screwy stuff man. When you are driving, the accessory belt is turning the alternator faster therefore creating more power output so thats gonna be normal to be a little higher when the RPMs are higher but still, just it being really low at idle/startup leads me to agree with some of the others that its got to be either a bad alternator or bad wiring/connection somewhere.

VENM505

 

[VENOMOUS1 RACING]

Apparently it was low before I bought it? Just cycling through pics.

That's just key on battery voltage bud. That appears normal. A bad cell can do weird things on our electrical system although like other mentioned, the alternator runs all electrical system. I would try a different battery just to rule it out. Easy swap

 

[tank86]

Ok, at least we have narrowed it down to: wiring, alternator, or battery.

 

[tank86]

I was hoping this was a pre existing problem from the photo, then I could narrow it down, whether my wiring (which is shady as hell) or the previous persons. That way I knew specifically whose to check.