I do not have a 6.2 in a M715. However, I have gone from zero 6.2 experience to owning 3 vehicles with them and working on a few others in the past 15 months. I just wanted to pass on a few things I learned because a lot of us are thinking 6.2 in our M715's and it will apply.
The Injection Pump is super critical to how the engine runs, starts, sounds, idles and just "feels" when you are behind the wheel.
I had a M1010 (CUCV ambulance) at my house for the past 9 months. I was to paint it and make it run better. My first drive did not impress me. The thing was a dog, hard to start hot, lost power when the throttle was released and felt like it couldn't get out of its own way. I put a brand new IP on it and WOW. That truck felt totally different, took less than a second to start hot or cold, purred like a hungry cat and actually went somewhere.
The owner came and got it yesterday. Between the body work and the IP, he said it was like having a whole new truck the differences were so great. This was after he drove it 150 miles home through the hill country.
My M1009 was getting 20-22 mpg running 60-63 highway with stock 31x10.50 tires. About a year ago I started smelling diesel after driving it once it got below 50° outside. I also found the tires I wanted at a great price. I haven't been above 19.8 mpg since the BFG 33x12.50 AT tires were put on. This is running the same gps monitored highway speeds. Which is a 6% rpm decrease because of the bigger tires.
The ip was leaking at the throttle shaft seals. Just a few drips on some days, never a river. The idle was never steady. Sounded like a gas engine set at about 25° initial timing trying to idle. It still ran down the road great, just not as easy on the fuel as before.
Because I was doing it for another person, I had to get the 1010 done first, it got the pump first. I finally saved up the money and installed mine Friday. Totally different truck. A hill leaving my house I used to have to kind of push the truck up to the speed limit was run this morning with me trying to slow it down to the speed limit. Idle is smooth as glass, constant sound out each exhaust pipe, no diesel smell or pool in the valley and lots more power at all speeds. I will post up about the expected mpg gains. If I can stay out of the fun pedal that is.
The M1010 and the M1009 are both 1985 model trucks. The 1010 had 37K miles and the 1009 has 83K. Miles don't really matter with these things. Years do. Both pumps were stock as near as I can tell. 25 years is way to old for these things based on my experience. I would almost call a 10 year limit if I get any more of these things.
Which I just did. The payment for doing the work on the 1010 was another 1009. The new 1009 which we call RED beause it is all red and a former fire truck also has a very new and shiny IP. I found some of the records in the floor board, but I think they put on the IP in 2007. Good enough for me.
My other 6.2 truck. A 1984 USAF Suburban looks to have the stock pump in it. It starts and runs great. However, I can move the throttle open some with my hand. Such as when I am charging the a/c system yet again after another part decided to leak. Holding it steady open a little and after a few seconds, the rpms will slowly start to climb. The IP is letting me know it wants to die.
Not trying to rant or lecture. I just keep telling myself this. How often have I changed plugs, cap, rotor, points, wires, set the timing, messed with advance weights, vacuum advance cans, tuned carbs, replaced jets, set the idle and mixture on a gas engine every 5-10 years? Well, the IP on a diesel is all that plus a pump and has even more exacting tolerances.
If you have a DB2, or a VE on a Cummins. Which by the way covers all US made diesel truck engines up to 1994. Unless you know the pump is less than 10 years old. I would suggest you start saving money, shopping around and making friends with your local Stanadyne guy. You will thank me the first time you drive the darn thing.