That sounds like a plan, but, remember that the problem may be the corrosion and resulting resistance in the positive cable. Be prepared to go straight to the starter, with good cables before you condemn the engine. I really don't see how any amount of juice would start a cummins engine that was internally locked up, even partially...Mark Edit: And continue running...

 

I have had people install the wrong size bearings on the lower end making the engine extremely hard to turn over but it would still run once it was started but with difficulty.

Do a voltage drop test across the battery cable from starter to battery terminal when trying to start the truck, this will rule out corroded terminal or bad connections.

What type transmission?

 

Jim,
The trans is an auto.
Removed the serpentine belt this morning and don't see any problem with the items connected to it.
If I remove the injectors should the engine turn over easy by hand with the correct lower end bearings or the wrong ones?
Still want to do a compression test.
I did try to start it without the existing cables.
Will a milled head or thinner head gasket create a hard start?

 

Removing the injectors would help if it was a high compression or hydrostatic issue by relieving the compression.

Milling the head could raise the compression ratio high enough to start hard but don't know why someone would do that intentionally to a street engine, that would also have to include lots of other work to the head and pistons.

 

Next thing you might try is to turn the engine manually using a socket and breaker bar on one of the harmonic balancer bolts. You can get a feel for how much strength it takes to turn the engine, and compare it to your other truck.

 

Modified an old injector to check cylinder compression.
The following is what I found:
1-450 psi
2-460
3-460
4-460
5-430
6-460
Still had to use two batteries to turn the engine over with the modified injector.
How is the compression?

 

If it's still hard to turn over with the injectors out then you have a dragging starter.

 

My truck just went though an issue with the starter not functioning properly, and it was as simple as a melted wire that led to the starter relay, once the harness was exposed. The relay had failed after 24 years, and the wire that leads to the starter solenoid melted up near the relay. Once the relay and wire were replaced, it starts perfectly.

The hog end of the wire that was bolted to the starter was corroded as well.


Personally, I would keep it simple, and do the simplest things first before going all ape crazy looking for odd stuff. A barring tool, or socket on the crank pulley to see how easy it turns is least invasive. Then bypassing the starter solenoid wire, after cleaning all the connections would be my second move. If the battery is over 3 years old, I'd have replaced that first.

Looks like you're doing a combination of all of this.

 

Its not the starter because I also switched the starter from my truck into it and still had to use two batteries.

 

Next I will try the barring tool on my truck and it to compare the difference.
If they are the same I will make up a new cable using welding cable for the plus side.

 

Used the Barring Tool on both trucks.
My truck turned easy.
The two battery truck was 20%-30% harder to turn with a 3/8" drive instead of 1/2".
Next well change the positive cable.

 

Changed both cables and still well not run on one battery.
I have run out of things to check?