Our 6.9 cranks slowly. I've done a lot to improve it. But it still cranks not as well as I'd like it to, or as well as our 7.3 does.

• New batteries
• New gear-reduction starter (this made an improvement)
• New battery cables (done by PO)
• New voltage regulator
• Battery terminals cleaned and coated with copper conductive lube

Still she cranks slow. I'm just thinking out loud with y'all about what it could be. I suspect it's both the alternator and the positive lead to the starter.
Here are voltage readings this morning, 58F cold start.

• 12.6v before turning the key
• 11.6v when the glow plugs kick on before starting
• 12.0v to 12.8v after startup, with glow plugs still cycling
• 14.3v at idle after a minute
• 14.6v at 1200 rpm

I suspect that the alternator is a bit weak. I'd rather see 12.9v or 13v in the morning. Check out the pic, it looks old. It's not delivering full amps at idle. I'm looking for a good price on a quality alternator.
I also suspect that the PO should have used thicker gauge wire for the starter lead. It must carry the current from both batteries to the starter. I'm thinking of making up a thicker cable.

What are your thoughts?

 

You can rule out the alt (that should get a 3g alt upgrade anyway though.There's no reason any IDI engine on the road doesn't have this affordable swap done by now really) by just charging the batteries overnight with a charger.If it then turns over super fast,then there ya go.
Do you know what size cables those are? Factory was 2/0 between bats and 3/0 down to starter but 2/0 overall is ok and is what the latter IDI's all got.

 

I agree that the positive cable down to the starter looks wimpy. 00 or better yet 000 is the way to go. What FordF250HDXLT said is spot on!

 

I get 14.7volts at idle with my 30$ junkyard 3g and it's been going fine for a couple years

 

Have you checked the starter solenoid on the fender? If the contacts are bad/corroded inside then that would kill your amperage going to the starter when cranking.

 

Yep, the cables are too small, and more importantly there looks to be a ring connector at the cable to the battery side to the starter lead.

That's the big choke point, cable going straight to the post clamp like as is going to the spare battery, and bigger cable - is the fix.

If you need to, use a ring connector to the second battery instead of the lead to the starter as the PO had done.

 

OE cable setup - cranking fast off single XL Start / Deep RV battery

 

I should have been more complete in the initial post. All connections are clean, dabbed with copper conductive, and tight.

That ring connector could just be it. I need a double ended post, don't I.

By 3g do y'all mean 1-wire alternator, with integrated voltage regulator?

 

Essentially that's what it is but it's Ford's alternator found on various 90's vehicles, the regulator screws to the back of the alternator so it's easy to change as well. Mine came off a mid 90's van with the inline 6. It bolts in and lines up perfect

 

I got my 3G alternatoe off of a mid 90s Ford Taurus with the 3.8l v6. Why your pulling parts off of it you should take the electric fan too. It's a hi quality unit!

 

I have a concern that my high-compression 6.9 diesel would be happier with an alternator of at least 150 amps. The minimum on a PSD is 110a, iirc. Perhaps the answer is to look for a CVPI alternator for my 6.9

 

I'm telling you, the 3G alternator swap is the way to go. They're rated at 130 A for the 94 Taurus.

https://www.rockauto.com/en/catalog/...generator,2412

C'mon man. Evreybodys doin' it!

 

With my 130 3g (which is the large frame version everyone is using) I can turn everything on and even with a large speaker system the light never dim even at idle. Iirc the 3g puts out like 2/3's of that 130 at idle

You may be able to score a leece neville ambulance alternator off of an ambulance at a junkyard. There just shy of 200 amps

 

The ring terminal has nothing to do with it, I don't even understand why someone brought that up. If they are talking about the smaller wire, its on the outside of the bolt from what I can tell, which is fine.

The bigger issue as stated is the small battery cables. Upgrade those and you'll be fine. O'reillys stocks one for about $80 if you have one near by. Other options include making them up from decent cable locally, with the proper size terminals. A ring terminal properly sized to the cable and bolt used is absolutely fine, and how most big rigs have their batteries connected.

Think of it this way, your battery is like a big water tank, the battery cables are hoses hooked off the tank, and the alternator is the pump that fills the tank. No matter how big a pump (alternator) you hook up to your tank to keep it full of water (charged up) if you only have a normal garden hose, you're not going to get the volume/pressure of water a firehose would provide. Our IDI starters need a firehose to spin quickly. Anything smaller than 2/0 is restricting your starter, and slowly killing it by not providing sufficient current, which will cause a voltage drop.

Here's a quick way to test this, you say your other truck cranks faster, swap the cables over and see what happens.

 

All great advice, gentlemen, and I thank you. We did a visual between the 7.3 that cranks nicely and the 6.9 slow cranker. Indeed, the wires on the 6.9 are thinner. I tried O'Reillys today for that cable, $85 but it was out of stock locally. I tried AutoZone but they have only adaptable cables etc. NAPA is closed on Saturday, natch. I tried 1A our sponsor, no luck, JC Whitney has it but for $90 plus shipping.

I wound up with RockAuto for $66 including shipping. I try not to use them much anymore since they went to bot-based customer service. But this time I really want that cable. Fat, molded, OEM quality, split-loom already in place. Some guys like ****, I like auto parts.

I'll post again once we install it. And start looking for an ambulance alternator.