Battery Voltage at Start-up.
Thread Starter
|
Junior User
Joined: Oct 2010
Posts: 64
Likes: 0
Battery Voltage at Start-up.
What is the minimum voltage we need to see at start-up. I have a CTS and it is showing 11.8 v and after the truck starts it stays there for roughly half a minute or more then it jumps right to 13.9 v. Is it the glow plugs dragging this down?
Hotshot
Joined: Jul 2005
Posts: 13,834
Likes: 25
From: Middle Tn.
Healthy batteries will show approx. 12.7 after sitting over nite. When you start the truck voltage will drop into the 11's till the gpm times out and then will jump to anywhere between the hi 12's to the low 14's depending on load and batteries.
Thread Starter
|
Junior User
Joined: Oct 2010
Posts: 64
Likes: 0
Elder User
Joined: May 2008
Posts: 765
Likes: 0
From: Patricia, Alberta
I never knew why that was happening when I first got my truck. I was watching the yard apes boosting all the trucks at the auction where I bought mine, they'd boost it, wait 30 seonds, pull the cables off, and the trucks would quit. I asked one of them why, and he said "the computer runs the alternator, and it won't let it charge till the motor's been running a while".
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
The yard ape was incorrect. There is no connection between the PCM and the alternator, except on dual alternator setups. On dual alternator setups, the PCM prevents the lower alternator from charging until the glow plugs turn off.
Elder User
Joined: Sep 2004
Posts: 821
Likes: 1
From: Nashville
What is the source of this info? I have a Ford bodybuilder's bulletin that says the PCM randomly selects one of the alternators while glow plugs are active. Did Ford reprogram the PCM to prevent lower alternator from charging somewhere along the way?
Trending Topics
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
This is from the service manual for a 2004. It's entirely possible that it's different for other years.
I suppose it's possible that Ford changed the way this works with later PCM flash updates also.
I suppose it's possible that Ford changed the way this works with later PCM flash updates also.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
Elder User
Joined: Sep 2004
Posts: 821
Likes: 1
From: Nashville
Thanks for sharing that doc, David. Unless this bulliten was just wrong to begin with, I guess they did change something.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
That's interesting. It wouldn't be the first time that I've found errors in the service manual.
It is also possible that the '04 and maybe later was different, since that bulletin was published in '03. Someone with dual alternators would have to get out the VOM and do some testing to know for sure.
I'm pretty sure my original post is correct, though. That the single alternator system is not controlled by the PCM.
It is also possible that the '04 and maybe later was different, since that bulletin was published in '03. Someone with dual alternators would have to get out the VOM and do some testing to know for sure.
I'm pretty sure my original post is correct, though. That the single alternator system is not controlled by the PCM.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
I suppose their might be readable PID's from the PCM that indicate which alternators are turned on, but you'd need something like AutoEnginuity to read them.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
13.7 after the glow plugs shut off is good. Unless you're having some other problems I don't see why you need to do anything.
Tuned
Joined: Jul 2006
Posts: 262
Likes: 2
I'm not too worried about the alternator but 11.4v with the truck off is considered a dead battery. If I'm not mistaken, a batteries resting voltage should be north of 12.5v to be considered good.