Why SDs have a wimpy alternator - long post from FTE

Ferdy Mint

Full Access Member
Joined
Aug 12, 2021
Posts
125
Reaction score
36
Location
Central Texas
This post really hit me because 1) we like Fords and 2) all our trucks are Fords, but FURD REALLY SCREWWS UP SOMETIMES.

You should really read the FTE thread, it's long but good stuff. I'll summarize. Ford put a little alternator in the SD 7.3 to protect the GPs, which were not engineered to run after the motor starts up. Beru designed the GPs to run on 11 volts, which is what you'd get when cranking with good batteries. The GPs are actually rated for 11V, not more. Then Ford in its corporate wisdom decided to have the PCM keep the GPs running long after the motor starts, to pass EPA standards. On my 2000 I see the GPR holding on for about 30 seconds after a cold start, which is useless to me. Ford even runs the GPs when you let off the throttle. And all that is for emissions crapola, don't get me started.

The alternator on an SD is only 110 amps, and I always wondered why. An OBS 7.3 gets 130 amps, and in general has less electrical stuff running, its fuel pump is mechanical for example. So why did Ford put in such a small alternator in the SD? It's because the GPs were not built to run after the motor starts up, so they are sitting there in the combustion chamber, diesel firing off around them, the alternator is spinning, and they are still heating from the PCM running the GPR. That was all Ford's decision. So they get too hot, which shortens their life. The small alternator keeps the running voltage down under 12. Mine hovers around 11.5 or so with a good alternator I put in last winter.

What a rotten decision, when Ford could have put in a newer Beru GP like the 6.0 got, that will not be damaged by running after the motor starts. It's one of those face palm moments when you learn.

The easy solution is to put the GPR ground wire on a switch in your cab. Keep it off most of the time unless the weather is cold, and switch it off as soon as the motor fires up. Or you can just use a springy push button that you have to hold to fire the GPs. We run that already on IDIs to prolong GP life, some of our IDIs use 6v GPs.

Once you put manual control on the GPR ground, then you can install a bigger alternator. 160 amps sounds about right to me. Especially if you have extra upfit equipment on your truck, a big stereo or CB amp, lighting, winch, whatever.

Here is the FTE post. https://www.ford-trucks.com/forums/...t-glow-plugs-hope-you-guys-can-get-along.html
 

Farmer Rock

just a fella' without a 10mm socket
Joined
Oct 27, 2020
Posts
1,423
Reaction score
1,313
Location
Glen Rock,PA
I installed an ambulance package alternator on my sd, 180 amp from Napa. Was maybe 10 bucks more than stock.
Very interesting thread though, I never knew about that.
Thanks for sharing this


Rock
 

MadMac

Registered User
Joined
Nov 24, 2021
Posts
63
Reaction score
25
Location
SMF
You should really read the FTE thread, it's long but good stuff.
The FTE post is _highly recommended_ deep reading. Copying the link here for ease of use.

Having read the entire +80 post chain (~40m) - if you have ANY issues with GPs, GPRs, Batteries, and to a lessor extent - starting problems - Please read the entire FTE chain, or at least to ~60. Even if its 5 years old.

There is so much background about the behavior and interaction of the components, that it will educate you as to which ever implementation generation of GP/Controller/Alternator you may have in your truck, be it 85 to 03.

Why it mattered to me: I spent ~10 years rehabilitating my 85 (i'm a weekend wrench, and not always a good one at that). I used a manual momentary switch for a long time, including replacement to a 4-0 copper setup, and high grade batteries, two alternators, GP harnesses, blah blah blah. And a bunch of GP replacements, including one broken off tip, which required a trip to the shop to open the exhaust valve to fish it out...

After everything started working really well - I converted the truck back to use the original GP controller - because I'm not the only one driving the truck, and I don't trust anyone to use a manual GP switch correctly. Essentially - less risk in the controller blowing up, than in one of my in-laws or my wife melting all the GPs in place... an ugly no-win and very necessary decision.

The one behavioral change which resulted - wait 30 seconds or at least 3 cycles of the GPR. This simple change has made starting incredibly reliable. In winter - use the block heater. I also put it on a battery tender. And for gawd sakes - only use the BERU spade plugs. Another observable change - is it smokes until the engine is really warmed up - which takes about 20 minutes under load. My lovely better half complains about it bitterly, but with the system now essentially bullet proof - worth the discussions...

All this prepares me for what to do in my newly acquired '97 OBS. I'm going the route of a spring loaded momentary cutoff switch. Its not likely to be needed - but I'm also not that impressed with all the shenanigans Ford went through throughout the lifespan of the diesel motors from 2003 back...

Point is - knowing how all those GP systems work - will help you understand how the system in your own truck should work...

Thanks to @Ferdy Mint for bumping the issue...
 

greenskeeper

Full Access Member
Joined
Mar 16, 2013
Posts
995
Reaction score
202
Location
PA
Alternator size has never has been an issue in my SD compared to my OBS

I've always had the PCM ground wire to the GPR on a switch in the cab. Only use glow plugs below 40F and when I do use them, kill the power just prior to cranking to save battery strain. Never use them for "emissions" reasons... let that baby smoke and **** off the enviromentalists until it's warmed up.
 

captain720

Full Access Member
Joined
Feb 20, 2022
Posts
589
Reaction score
448
Location
Washington
My IDI starts slightly better if I stop glowing just before cranking on the manual controller I assume the PSD would be the same.
 
Top